Intelligent automatic transfer switch module

Abstract

An automatic transfer switch (100) is provided for automatically switching an electrical load between two power sources. Two power wires (106) enter the ATS (A power input and B power input) and one wire (109) exits the ATS (power output to load). The ATS has an indicator (107) located under a clear cast plastic lens (108) also charging the air intake. The ATS (100) also has a communications portal (103) and a small push button (104) for direct input of some local control commands to the ATS (100). The ATS (100) can be mounted on DIN rails at the rack and avoids taking up rack space.

Description

[0001] Cross Reference to Related Applications

[0002] This application claims priority to U.S. Provisional Application No. 62 / 820,726, filed March 19, 2019, entitled “INTELLIGENT AUTOMATIC TRANSFER SWITCH MODULE.” The contents of the above-identified application (“parent application”) and priority to the parent application are hereby claimed and incorporated by reference herein to the fullest extent allowed by applicable law and regulations. The entire contents of the parent application are incorporated herein by reference.

[0003] Incorporation by Reference

[0004] The systems, components, and processes described herein build on and can be combined with some of the technologies of the Zonit Structured Solutions (Zonit) to produce a synergistic effect or combined advantage, such as increasing the efficiency of rack space, reducing the rack size for a given payload equipment, enhancing functionality, enhancing networking and monitoring of equipment, reducing equipment requirements and costs, and others. Accordingly, the following families of Zonit’s U.S. cases (patents and applications) are referenced at various points in the description (intended to reference all related U.S. applications and patents available for incorporation by reference in each family), all of which are hereby incorporated by reference in their entireties.

[0005] 1. U.S. Patent Application Serial Nos. 60 / 894,842, 12 / 049,130, 12 / 531,212, 12 / 569,733 (ATS Cases);

[0006] 2. U.S. Patent Application Serial Nos. 60 / 894,844, 12 / 531,215, 13 / 889,181, 15 / 353,590, 14 / 217,225 (Z-cool Cases);

[0007] 3. U.S. Patent Application Serial Nos. 60 / 894,846, 12 / 531,226, 12 / 569,377, 13 / 757,156, 13 / 763,480, 14 / 717,899, 15 / 655,620, 15 / 656,229 (Smart Outlet Cases);

[0008] 4. U.S. Patent Application Serial Nos.: 60 / 894,848, 12 / 531,231, 12 / 569,745, 13 / 466,950, 14 / 249,151, 13 / 208,333, 14 / 191,339, 14 / 564,489, 15 / 603,217, 15 / 797,756, 61 / 970,267, 61 / 372,752, 61 / 372,756, 13 / 208,333, 61 / 769,688, 14 / 191,339, 14 / 564,489, 15 / 603,217, 15 / 797,756 (Auto Switching Cases);

[0009] 5. U.S. Patent Application Serial Nos.: 61 / 324,557, 13 / 088,234, 14 / 217,278, 15 / 250,523, 15 / 914,877, 60 / 894,849, 12 / 531,235, 12 / 568,444, 13 / 228,331, 61 / 610,183, 61 / 619,137, 61 / 799,971, 61 / 944,506, 15 / 064,368, 15 / 332,878 (Locking Outlet Cases);

[0010] 6. U.S. Patent Application Serial Nos.: 60 / 894,850, 12 / 531,240, 12 / 569,609, 14 / 470,691, 15 / 673,153 (NetStrip Cases);

[0011] 7. U.S. Patent Application Serial Nos.: 61 / 039,716, 12 / 891,500, 13 / 108,824, 14 / 217,204, 14 / 680,802, 15 / 450,281 (Power Distribution Method Cases);

[0012] 8. U.S. Patent Application Serial Nos.: 61 / 040,542, 12 / 892,009, 13 / 108,838, 14 / 327,212 (UCAB Cases);

[0013] 9. U.S. Patent Application Serial Nos.: 09 / 680,670 (ZPDS Cases);

[0014] 10. U.S. Patent Application Serial Nos.: 14 / 217,159, 15 / 452,917, 14 / 217,172, 15 / 425,831, 14 / 217,179, 15 / 706,368 (Relay Cases);

[0015] The parent case and the other cases mentioned above are sometimes collectively referred to herein as Zonit Cases. BACKGROUND

[0016] Electronic data processing (EDP) equipment, such as servers, storage devices, etc., are typically powered by alternating current (AC) power sources in data centers, which require very high reliability. For this reason, the equipment is typically fed by one or more uninterruptible power supplies (UPS). When a data center is supplied with redundant power sources (e.g., A power source and B power source), the data center manager must manage the supply and capacity requirements of both power sources. The supply must be such that if either of the two power sources fails, the remaining power source has sufficient power capacity to carry the total load of the equipment. However, the complexity of delivering power from the UPS to the equipment often creates the potential for many interruptions. For example, power distribution circuits, temporary circuit breakers, power strips, power whips, power distribution units (PDUs), power panels, power cords, non-locking or locking, and other distribution elements are often placed in the circuit path between a large UPS system and the EDP equipment. These components increase the probability of the equipment being interrupted or disconnected from power. EDP equipment can contain dual power supply arrangements that provide direct current (DC) power to the internal circuits of the equipment from two separate AC sources. Additionally, the UPS system and other power distribution components require maintenance, which can require them to be taken out of service.

[0017] Under this arrangement, a failure in one of the AC sources will result in the equipment load being supplied by the backup DC power supply in the unit. While both AC sources are present, the load is either shared by both power supplies or biased to one of the power supplies. These systems, sometimes referred to as "redundant supply" systems, can be the last line of defense for reliable power delivery to the electronic circuits within the equipment. However, these solutions can be costly due to the additional power supplies that can be required. Additionally, the increased components generate more heat, which is undesirable in many applications. Furthermore, the EDP equipment can only include one power supply and one AC power input. In this configuration, the equipment is vulnerable to a single AC source failure. Additionally, components added to address this weakness, such as an automatic transfer switch, can require rack space, which is expensive.

[0018] Gathering multiple such affected EDP equipment onto a multi- outlet power distribution unit (PDU) and feeding the PDU from a switching device, such as an automatic transfer switch (ATS), which selects from the available power sources (e.g., A or B), is an alternative means of delivering redundant power to the EDP equipment while reducing the number of power supplies, cords, etc. Due to cost and efficiency, it can be a superior approach for many deployment scenarios, such as large server farms.

[0019] In another application, many industrial devices that have been in service since the 1960s have incorporated intelligent control modules that use digital processing components, such as one or more single-chip microcontrollers (MCUs) or other digital processing components. The Intel 8051 is a well-known and widely used example of this type of component. These components have seen great improvements in computing power and capabilities, accelerated by the cell phone revolution, for example, cell phones use many ARM-32 and ARM-64 MCU components. The increased computing power of these components has allowed them to execute programmed logic that is much more complex and capable. Ensuring that intelligent control modules have maximum uptime can bring many benefits. Many of the failures of long-service-time modules occur at power-up. Therefore, avoiding unnecessary restarts or restart cycles can improve reliability. Many of the software algorithms used with control modules “learn” as they run, and when the module is restarted due to power distribution maintenance, UPS maintenance, UPS failure, or power failure, some or all of the learning can be lost. The use of a proper ATS unit in the power path of the intelligent control module(s) of these industrial devices can eliminate these potential problems, maximizing uptime.

[0020] It should be appreciated that notebook / desktop / server computers, single-board computers (SBCs), systems on a chip (SOCs), microcontroller units (MCUs), and other similar components are all, in essence, digital devices that are capable of executing programs. Further, SBC units, SOCs, MCUs, and other similar digital processing components are rarely built into computing devices that are designed with dual power supplies. All of these computing devices can run programs and can benefit from improved uptime by proper use of the proper automatic transfer switch units described herein. The benefits of uptime are obvious for any digital processing device with a single power supply, but can also benefit digital processing devices with dual power supplies.

[0021] It is in this context that the automatic transfer switch modules described herein were developed. SUMMARY

[0022] Embodiments and aspects of the invention are described and illustrated below in connection with systems, tools, and methods that are exemplary and illustrative, and not limiting in scope.

[0023] According to one example of the present application, an automatic transfer switch is provided for automatically switching an electrical load between two power sources. The automatic transfer switch includes a switch module, and a primary input power line and a secondary input power line, each attached to the switch module and each for receiving power from a different one of the two power sources. When used in a data center environment having A-B power sources, it is desirable to positively manage the load of the A power source and the B power source. The automatic transfer switch can preferentially use the A power source (i.e., the primary power source) when it is available, and use the B power source (i.e., the secondary power source) only when the A power source is not available. Conversely, the automatic transfer switch can preferentially use the B power source (i.e., the primary power source) when it is available, and use the A power source (i.e., the secondary power source) only when the B power source is not available. For example, the source having the voltage or any other power quality characteristic or combination of characteristics that is best suited for the EDP equipment load being fed can be preferred as the desired source. The automatic transfer switch can also make this determination of power source preference based not only on availability, but also on the quality of the power. The ATS can be designed to allow the data center manager to select which power input is the preferred input. This can be done through explicit interaction with the ATS unit (e.g., through a manual power input selector, a graphical user interface object, or other user control), automatically (e.g., in response to sensed electrical conditions or environmental sensor inputs), or through remote control via remote EDP equipment, such as the Zonit control module described below. This is desirable so that the data center manager can allocate the capacity of the power distribution system with the assurance of what source will normally feed these connected loads. The automatic transfer switch can also make the selection of what source to prefer based not only on availability, but also on the quality of the input power. For example, the source having the voltage or any other power quality characteristic or combination of characteristics that is best suited for the EDP equipment load being fed can be preferred as the desired source.

[0024] The automatic transfer switch also includes an output power line (or one or more output receptacles) attached to the switch module for supplying power to the electrical load. In addition, the automatic transfer switch can include one or more relays (e.g., mechanical relays, solid state relays, or a combination of both) disposed within the switch module and coupled to the primary input power line. The relays are operable to sense suitable power delivery characteristics (i.e., quality) on the input power line and automatically couple the output power line to the primary input power line or the secondary input power line depending on one or more values of the input power quality.

[0025] The automatic transfer switch can also have one or more communication mechanisms that allow it to interface with remote EDP devices (such as Zonit control modules, for example) to enable monitoring, control (including configuration), and reporting on the automatic transfer switch via remote and / or local electronic means. This can enable reporting of any power quality characteristics measured or observed at the ATS, the condition of connected EDP equipment, and any power quality characteristics affected by the load of the EPD equipment(s). It can also include other variables such as the hardware and software health of the ATS unit and internal environmental conditions, or connected devices with appropriate means. Any other information desired about the ATS unit and its components, such as the performance and condition of cooling fans, can be supplied. If desired, the ATS unit can be equipped with connections for additional sensors, such as environmental (temperature, humidity, moisture presence, smoke detection), security (door lock status, moisture presence, smoke detection), or other sensor types as needed. If desired, the ATS unit can provide the required information to perform electricity usage measurement and billing functions. The ATS unit can report any or all information collected to remote EDP devices as needed and desired, where it can be processed, displayed, and acted upon as needed. Additionally, the ATS unit can process information and take action as desired, generating alerts or using other condition information, to be displayed by the ATS unit.

[0026] The ATS unit can contain the ability to sample at high resolution, in one example 15 kHz, the waveforms of one or more power inputs and / or the power outputs of the ATS. An example circuit that can be constructed for this purpose in a small space, with a low power budget, at very low cost will be described later (which makes it possible to incorporate into any of the inventions described herein and possible examples thereof). This sampling rate is sufficient to provide very detailed information about the power quality of the input source(s) and / or connected output load(s). This level of sampling is equivalent to high-quality specialized power quality analysis instruments such as those provided by Fluke, Tektronics, and other manufacturers. Furthermore, this same level of power quality measurement can be embedded as an optional capability into the power distribution equipment described in the Zonit cases, which are already fully incorporated. Embedding this level of power quality measurement into the power distribution system of a data center, factory, office, or home enables the broad capabilities described in the Zonit cases.

[0027] The automatic transfer switch can be implemented in a relatively small device that is suitable for deployment in less than a full 1U of rack mount space, or adjacent to rack mounted electrical equipment, or similar to a PDU associated with that electrical equipment. It can be used in any structure suitable for supporting electrical equipment (e.g., 2-post equipment racks, 4-post equipment racks, various types of cabinets, or similar structures). It can be installed in a partial 1U space that has already been used by EDP equipment sections (thereby not sacrificing any 1U of rack space), or in a partial rack that is not used when installed. In some instances, the switch module can occupy less than 85 cubic inches for a single phase configuration, and 150 cubic inches for a three phase configuration. In this regard, the automatic transfer switch can not require installation space in an equipment rack, which can reduce cooling issues associated with large components and long power wires used in traditional designs. Due to the use of modern solid state components and innovative design, this switch can also consume relatively small power (less than 2 watts in some instances) compared to other automatic transfer switches.

[0028] Multiple instances of the automatic transfer switch can be created depending on the needs and requirements of the application. Figures 18-20 Various possible instances are shown in the figures. Some instances can be single or multiple phase power ATS units. These instances have multiple possible form factors, some of which are capable of zero U type installation, some are rack mountable, and some are small enough to be conveniently embedded in an industrial device, such as a control module housing or the chassis of that industrial device, as described in more detail in the Zonit cases. This small form factor is very important, as rack mounted ATS units can be difficult or impossible to integrate in many types of applications. Some instances can have features suitable for use in industrial devices, such as DIN rail mount compatibility, either by having integral slots in the chassis to accept standard dimension DIN rails, or using DIN rail adapters that can be mounted in the integral slots. Some instances of the ATS unit can contain wiring boards instead of input and / or output wires or sockets, as this can make connection of the ATS unit to the wiring harness of an industrial device or other application more convenient.

[0029] According to another aspect of the present application, an automatic transfer switch is provided for automatically switching an electrical load between two power sources. The automatic transfer switch includes a switch module having a footprint of less than 85 cubic inches. The automatic transfer switch also includes a primary input power cord and a secondary input power cord, each attached to the switch module, each for receiving power from a different one of the two power sources; and an output power cord attached to the switch module for supplying power to the electrical load or to a PDU capable of supplying power to a plurality of EDP equipment loads. Further, the automatic transfer switch includes one or more relays contained within the switch module and having a voltage sensitive input coupled to the primary input power cord for coupling the output power cord to the primary input power cord when one or more power qualities of the primary input power cord are acceptable and for coupling the output power cord to the secondary input power cord when one or more power qualities of the primary input power cord are not acceptable. Further, the primary and secondary sources are selectable as to which of the physical "A" and "B" inputs are assigned to the automatic transfer switch.

[0030] According to another aspect of the present application, an automatic transfer switch (Zonit μATS-Industrial TMAn automatic transfer switch (e.g., the Zonit® ATS 1500®) for automatically switching an electrical load between two power sources. The automatic transfer switch includes a switch module that occupies less than 150 cubic inches of space. It can provide a range of ampacity capacities as needed, but is still small enough to fit easily into an industrial control enclosure or cabinet. It can be mounted directly or via an adapter on a DIN rail. It can have a high MTBF and a wide operating temperature range, suitable for industrial equipment environments. The automatic transfer switch also includes a primary input power cord and a secondary input power cord, each attached to the switch module and each for receiving power from a different one of the two power sources; and an output power cord attached to the switch module for supplying power to the electrical load; or alternatively a terminal block for input and output power connections. In addition, the automatic transfer switch includes one or more relays contained within the switch module and having a voltage sensitive input coupled to the primary input power cord for coupling the output power cord to the primary input power cord when one or more power qualities of the primary input power cord are acceptable, and for coupling the output power cord to the secondary input power cord when one or more power qualities of the primary input power cord are not acceptable. The relays can be designed to open when control logic is not operational, which is the default for most ATS units. This guarantees that if the ATS unit has a logic problem, it will not deliver power. In addition, if only one source is energized, both the primary and secondary sources can power the unit. The unit can be equipped with a fuse and virtual circuit breaker w / reset button (as described in the Zonit case, incorporated by reference in its entirety) or one or more small form factor circuit breakers. In this way, overload protection is provided. Each method has advantages. The automatic transfer switch can provide clear, visible status indicator lights that can be seen regardless of the angle or orientation of the automatic transfer switch. This allows a wide variety of mechanical mounting configurations without affecting the visibility of the status indicators. The status indicator lights can be mirrored or replicated onto a remote display and / or remote management device(s) as desired for display as needed. The status indicator lights can indicate which power input source is currently in use. They can also show that an unused power source exists. This can be done by controlling the intensity, blink rate, pattern, or other visible parameters of the indicator lights. The ATS unit can also incorporate Zonit ZCrush circuitry to prevent the release of stored energy from a connected load through the ATS unit when the ATS unit is making a power transfer. Several examples of this phenomenon are discussed in U.S. Patent Application Serial No. 16 / 817,504 (the ZCrush case), entitled “Relay Conditioning and Power Surge Control,” filed March 12, 2020, which is incorporated by reference herein.A common practice for industrial control modules is to use a large filter capacitor across the AC mains input (similar to what is done in AC / DC power supplies as discussed in the ZCrush case) and / or step down the AC voltage to 24 or 48 volts via a transformer, which can typically store a large amount of energy in its core that can be discharged through the ATS unit when power conversion occurs. The ATS unit can also be auto-ranging, i.e., operate over a wide range of input voltages, such as 24-277V, 48-277V, 80-277V, or other desired voltage operating ranges. The unit can be designed to work using DC power or AC power.

[0031] According to another aspect of the present application, there is provided an automatic transfer switch (Zonit μATS-V2 TMAn automatic transfer switch (e.g., the Zonit ATS-1500®) for automatically switching an electrical load between two power sources. The automatic transfer switch includes a switch module that occupies less than 150 cubic inches of space. It can provide a range of ampacity capacities as needed, but is still small enough to fit easily in an EDP equipment rack or enclosure. It can be mounted on a DIN rail directly or via an adapter in the enclosure. The automatic transfer switch also includes a primary input power cord and a secondary input power cord, each attached to the switch module and each for receiving power from a different one of the two power sources; and an output power cord attached to the switch module for supplying power to the electrical load. In addition, the automatic transfer switch includes one or more relays contained within the switch module and having a voltage sensitive input coupled to the primary input power cord for coupling the output power cord to the primary input power cord when one or more power qualities of the primary input power cord are acceptable, and for coupling the output power cord to the secondary input power cord when one or more power qualities of the primary input power cord are not acceptable. The relays can be designed to turn off when control logic is not operational, which is not the default for most ATS units. This guarantees that if the ATS unit has a logic problem, it will continue to deliver power. In addition, if only one source is energized, both the primary and secondary sources can power the unit. The unit can be equipped with a fuse and virtual circuit breaker w / reset button (as described in the Zonit case, which is incorporated by reference in its entirety). This is compatible with fail-close in the event of ATS control logic failure, as in this case the unit becomes the fused power cord on the side that the relays are not energized and turned off. In this way, overload protection is provided whether or not the control logic is working. The automatic transfer switch can provide clear, visible status indicator lights that can be seen regardless of the angle or orientation of the automatic transfer switch. This allows for a wide variety of mechanical mounting configurations without affecting the visibility of the status indicators. The status indicator lights can be mirrored or replicated to a remote display and / or remote management device(s) as desired for display as needed. The status indicator lights can indicate which power input is currently in use. They can also show that an unused power source exists. This can be done by controlling the intensity, blink rate, pattern, or other visible parameter of the indicator lights. The indicator lights can also indicate whether there is a power quality problem or whether the amperage delivered exceeds a given percentage of the ATS unit capacity. This is useful in load centers where EDP equipment is moved in and out of racks and the power delivered by the ATS unit can therefore vary. It can help data center workers not to overload the ATS unit. The ATS unit can also incorporate the Zonit ZCrush circuit to prevent the release of stored energy from a connected load through the ATS unit when the ATS unit is making a power transfer. Several examples of this phenomenon are discussed in the ZCrush case, which is incorporated by reference.The ATS unit can also be auto-ranging, i.e., operate over a wide range of input voltages, such as 24-277V, 48-277V, 80-277V, or other desired voltage operating ranges.

[0032] Still in accordance with another aspect of the present application, a method for providing power to an electrical device is provided. The method includes providing an automatic transfer switch having a first interface for coupling to a first power source, a second interface for coupling to a second power source, and one or more third interfaces for coupling to an electrical device to be powered. The automatic transfer switch is operable to automatically switch between the first power source and the second power source in response to an interruption in quality of a primary input power. The method further includes coupling the first interface with the first power source, coupling the second interface with the second power source, coupling the third interface(s) with the electrical device, and selecting one of the first power source and the second power source as a primary source. In addition, the automatic transfer switch, via electronic means connection with a remote management device, can also automatically shut off or turn on power to equipment connected to the output of the automatic transfer switch in response to a manual operator desire, or any number of other conditions deemed necessary by the remote control equipment and any attached sensor devices that can be monitored by the remote control equipment.

[0033] In addition, the automatic transfer switch has a clear and visible status indicator light that can be seen regardless of the angle or orientation of the automatic transfer switch. This allows for a variety of mechanical installation configurations without affecting the visibility of the status indicator.

[0034] In addition, the automatic transfer switch module can contain unique mounting slots that relieve the burden of physically and fixedly mounting the automatic transfer switch module to a fixed mounting location. These unique slots allow for the convenient attachment to the automatic transfer switch module using a variety of standard off-the-shelf hardware combinations without the need for special adapters or tools.

[0035] Still in accordance with another aspect of the present application, a system for powering rack-mounted electrical equipment is provided. The system includes a rack or cabinet having a plurality of power sources. In addition, the system includes an automatic transfer switch module including a first electrical line coupled to a first power source, a second electrical line coupled to a second power source, and one or more third electrical lines coupled to electrical equipment supported on one of the shelves of the rack or otherwise mounted on the rack or to a power distribution unit (such as a horizontally or vertically mounted panelboard or power strip) capable of delivering power from the output of the automatic transfer switch to the plurality of equipment. The automatic transfer switch module is operable to switch the supply of power to the electrical equipment(s) between the first power source and the second power source in response to an interruption in the current source of input power or other power quality characteristics of the input power. In addition, the automatic transfer switch, via local or remote means (by connection to a remote management device), can also be used to turn power off or on to equipment connected to the output of the automatic transfer switch in response to an explicit operator request (e.g., entered by a user employing a physical selector such as a button or switch or employing an electronic sensor such as an object of a graphical user interface) or automatically in the event of an over-temperature or fire / smoke detection or any number of other conditions deemed necessary by the ATS unit or by remote control equipment and respective attached sensing devices. The ATS can also include current limiting devices for limiting the maximum current across the equipment to remain within a defined range.

[0036] The automatic transfer switch has clearly visible status indicator lights that are visible regardless of the angle or orientation of the automatic transfer switch. This allows for a wide variety of mechanical mounting configurations without affecting the visibility of the status indicators. The status indicator lights can be mirrored or replicated onto a remote display and / or remote management device(s) as desired for display as needed. The housing can also include slots or other openings for dissipating heat generated by the ATS.

[0037] The automatic transfer switch module can provide unique mounting slots as part of its housing to ease the task of physically and fixedly mounting the automatic transfer switch module in a fixed mounting location. These unique slots allow for the convenient attachment to the automatic transfer switch module using a variety of standard off-the-shelf hardware combinations without the need for special adapters or tools.

[0038] The solutions we invented are innovative and offer considerable benefits. They include several electronic circuits that perform various functions. We describe their use below in the context of automatic transfer switches, but they may also be useful in other applications. The automatic transfer switches we use as illustrative examples may incorporate inventions described in PCT Application No. PCT / US2008 / 057140, U.S. Provisional Patent Application No. 60 / 897,842, and U.S. Patent Application No. 12 / 569,733, now U.S. Patent No. 8,004,115, all of which are incorporated herein by reference.

[0039] The circuit is described below in relation to an automatic transfer switch ("ATS") connected to two separate power sources, A and B. It should be noted that the example ATS is for single phase power, however, multi-phase ATS units can be constructed using the same circuitry, which would essentially be multiple single phase ATS units acting in parallel. The only change that would need to be made is to synchronize certain control circuits so that they act together across the multiple ATS units to handle the switching and return from the A multi-phase source to the B multi-phase source and vice versa. The only change would be to specify under what conditions the power sources are switched. For example, given a three phase source with X, Y and Z hot leads, a failure in any one of the three could be considered grounds for switching to the B multi-phase source. To return to the A multi-phase source, all three multi-phase leads would have to be present and of sufficient quality to return to the A source.

[0040] In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and study of the following descriptions. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] For a more complete understanding of the present invention and its further advantages, please now refer to the following detailed description taken in conjunction with the accompanying drawings, in which:

[0042] Figure 1 is a basic block diagram showing an overview of the electrical and electronic subsections according to the present invention;

[0043] Figure 2 is a detailed block diagram of an input disconnect switch and a synchronous detector according to the present invention;

[0044] Figure 2-A is a schematic diagram of one side of an input disconnect switch and a synchronous detector according to the present invention;

[0045] Figure 3 is a detailed block diagram depicting the various functions of the components of the input selector (gater) subsection according to the present invention;

[0046] Figure 3-Ais a schematic diagram of an input selection and power switching section (gate) according to the present application;

[0047] Figure 4 is a current sensing block diagram providing an overview of a current sensing arrangement associated with detecting the output current of an ATS according to the present application;

[0048] Figure 5 is an indicator and communication block diagram providing an overview of a communication arrangement and indicators used in an ATS according to the present application;

[0049] Figure 6 is a power supply block diagram providing an overview of various elements of a power supply system for powering an ATS and remote communication section according to the present application;

[0050] Figure 7 is a timing diagram providing an overview of the general timing and sequencing of events according to the present application;

[0051] Figure 8 shows a 30 ampere (amp) wired automatic transfer switch according to the present application, shown in perspective and left end view;

[0052] Figure 9 shows a 30 ampere dual IEC type C19 output, wired input ATS according to the present application;

[0053] Figure 10 shows a 20 ampere dual IEC type C20 input, single IEC type C19 output ATS according to the present application;

[0054] Figure 11 shows a circuit and method of detecting zero-crossing according to the present application;

[0055] Figure 12 shows how a synchronous detector circuit extracts the AC input voltage square wave according to the present application;

[0056] Figure 13 shows a cross-sectional end view of the enclosure of an ATS according to the present application;

[0057] Figure 14 shows the components of a relay contact authentication detection module according to the present application;

[0058] Figure 15 shows a block diagram of an ATS including a relay operation authentication function according to the present application;

[0059] Figure 16 shows a circuit for implementing a surge limiting function according to the present application;

[0060] Figure 17 shows a high definition waveform sensor circuit according to the present application;

[0061] Figures 18-20 Various examples of ATS according to the present application are shown;

[0062] Figure 21 Several options for utilizing ATS as described herein to increase uptime and maintainability of example SBC control modules are shown; and

[0063] Figure 22 Several enclosure or housing configurations according to the present application are shown. DETAILED DESCRIPTION

[0064] An automatic transfer switch system is described below that has several advantageous features related to data conductance, compact size, avoidance of use of valuable rack space, primary power selection, remote monitoring and reporting, maximum current control, etc. Specific examples embodying these advantageous features will be described below. However, it should be understood that alternative embodiments are possible in accordance with the claimed invention. Accordingly, the following description should be understood as exemplary, rather than limiting.

[0065] The primary function of the ATS is accomplished via a set of mechanical relays that transfer power from one source to another. In addition, the closure of these mechanical relays is augmented by the use of modern semiconductor switches, such as Insulated Gate Bipolar Transistors (hereinafter IGBTs), but these devices can be other semiconductor switches that have sufficient voltage and current handling capability, classed as TRIACS, SCRs, Bipolar transistors, Field Effect Transistors, or combinations of each. These switches can be configured in various ways, each with advantages and disadvantages. The preferred example for use in the present ATS is with IGBTs. They are chosen because they are easy to turn on and off, are structurally robust, and are resistant to false conduction.

[0066] The timing and execution of the required functions is accomplished with a digital control circuit consisting of a Peripheral Interface Controller or PIC. This device is a member of the "programmable function" family of devices, and allows a set of code to be recorded in the device that directs the actions of the entire digital control system. The PIC has sufficient computing power to perform certain mathematical calculations to allow for the precise calculation of voltages, currents, times, and other precise parameters that are necessary to very precisely control the timing of the relays and solid state switches.

[0067] The ATS also includes advanced communication capabilities via a connection to remote EDP equipment for the purpose of reporting status, electrical characteristics of the attached electrical "mains" and various other information content that can be useful in maintaining the electrical power system to which the ATS is attached, whether as a source power or as attached equipment (hereinafter referred to as "load"). This communication portal on the ATS utilizes an internationally recognized mode known as Universal Serial Bus (USB) as the primary communication means, and utilizes PICKIT programming transfer as a secondary communication protocol. This secondary communication includes allowing field upgrades without the need to open the ATS device to access a traditional programming port. A third communication means is also provided, allowing simple digital serial data to be transmitted and received by the ATS via un-encoded 5 volt logic levels. This third communication means is provided to allow interfacing with long line communication means. The USB transfer and protocol is not particularly well suited for transferring and receiving data over distances in excess of 10 to 30 meters. For applications requiring long distance communication in harsh environments, it is necessary to interface the signal to other various standards. The availability of the raw "serial data" through the communication port allows for simple and economical direct attachment of alternate transfer standard interfaces.

[0068] Description of Circuit Operation

[0069] Figure 8 A perspective and rear view of one example of the ATS 100 is shown. As shown, two power wires 106 enter the ATS (A power input and B power input), and one wire 109 exits the ATS (power output to load). Also shown in the figure is the indicator 107, which is located under a transparent castellated plastic lens 108, which also acts as an air intake. Also shown in the figure are the previously mentioned communication portal 103 and the small push button 104 for direct input of some local control commands to the ATS.

[0070] The internal assembly of the ATS 100 is equipped with a pair of small fans to provide cooling to the various components inside as necessary. These fans only operate when necessary and only at the speed necessary to maintain acceptable operating temperatures. Two fans are included to allow for redundancy, and the controller inside the ATS 100 can report any detected faults, including performance characteristics of either fan, to remote monitoring equipment via the communication portal. The temperature of the air intake to this unit, as well as the air exhaust, is also reported to the remote monitoring equipment.

[0071] Referring to Figure 7, an overview of the basic switching concept, a basic understanding of the operation of the ATS can be obtained.

[0072] Figure 7a The ATS is shown in the off state, with no applied power. Switches 2, 3, 91 and 92 are all open.

[0073] Figure 7b The condition is shown when power is applied to the A input. After the unit is powered on, the controller opens the A input switch 2, it also closes the input select switch 4 (hereinafter referred to as GK, an acronym for Gate Keeper), and allows the passage to the output through the GKA switch 91. Power can now flow from the A input to the output.

[0074] Figure 7c The condition is shown when power is applied to the B input. After the unit is powered on, the controller opens the B input switch 3, it also closes the input select switch 4, and allows the passage to the output through the GKB switch 92. Power can now flow from the A input to the output. When power is applied to both inputs, as in the normal condition, both input select switches will be closed and will deliver power to the GK 4, the controller will direct the GKA switch 91 or the GKB switch 92 to deliver power to the output. The GKA 91 and the GKB 92 must never be open at the same time. This would result in a short circuit of both inputs together.

[0075] Figure 7d The condition is shown when both the GKA 91 and the GKB 92 are closed at the same time. In this case, the fuse located on the side of the A input 12 is shown as "blown" or open. Since the GK has shorted both legs of the A input and the B input, the opposite side must also be protected. The B input also has a fuse 13 on one of its inputs, but it is on the opposite leg of the path. It is also shown as "blown" or open. These two fuses 12, 13 not only protect the load from being in a dangerous condition, but also prevent the input power from being severely overloaded in the event of a catastrophic failure within the ATS. Using this technique, all six legs, two in the A input, two in the B input, and two in the output, are protected in any combination of overload conditions.

[0076] Figure 7e The introduction of solid state switching elements 93, 94 is shown. Mechanical relays all require a finite amount of time to operate, either to close or open the contacts, after a signal is applied to the coil. Solid state switching devices typically have very short operating times, on the order of microseconds. However, they do exhibit a voltage drop across the junction when conducting (closed), and this voltage drop represents a loss of power in the circuit. For example, an IGBT based semiconductor AC switch, such as the one used in this example, exhibits a voltage drop of about 3 volts at a conduction power of 30 amps. This involves a loss of 90 watts. An equivalent mechanical relay would exhibit a loss of about 1 watt at the same applied current. Therefore, the use of solid state relays to augment the mechanical relays is the ideal combination for maximizing efficiency and operating speed. When conduction is desired, as Figure 7eThe conduction of current will begin within approximately 10 microseconds of the command to conduct in the enhanced relay configuration shown. This allows for precise timing of the connection to the power source. However, the disconnect time is still subject to the response time of the mechanical relay, as the contacts of the mechanical relay are connected in parallel with the SSR element. Even though the SSR element can be turned off, the mechanical contacts will remain closed for a short time before releasing. This delay has no impact when switching from one power source to another when both power sources are available, such as when the ATS returns to the preferred side after the preferred side restores power. In this case, precise disconnect timing can be achieved, as the mechanical relay can be commanded to release before the desired time of actual disconnection, while the SSR is still conducting. Then, at the desired disconnect time, the SSR can be commanded to release. Thus, in most conditions, precise timing can be achieved with little loss of power in this configuration. The advantage of using IGBTs and bridge AC switches is the ability to turn on and off in very short times. It is difficult to turn off a triac or SCR-based switch, as these devices want to remain on until the current stops conducting, so they remain on until the zero crossing point when the AC current changes polarity through the sine wave. In Figure 7e In the example shown, the SSR 93 on the A side is shown in the on condition and is conducting power to the output while the mechanical relay contacts of the GKA 91 are moving to attempt to turn off. Any timing variations that can result from the mechanical effects of relay contact movement are masked by the conduction of the SSR. Although there is an inherent power loss associated with the delivery of current by the SSR during this time, it is very short, approximately 10 milliseconds, before the mechanical relay contacts turn off, thus minimizing the power loss. The SSR can remain on, but it will have no effect.

[0077] Figure 7f The final configuration is shown with power being conducted to the output through the GKA relay 91 and bypassing the SSR 93.

[0078] Subcircuit Detail Description

[0079] Figure 1 The general configuration of all sub-circuits is shown, which helps to determine their function in the overall operation of the ATS. Note that both the A side AC power connection and the B side AC power connection go through the “N” side disconnect and synchronization generation sub-circuits 2, 3. When there is no AC voltage at the input of one or both of these circuits 2, 3, the mechanical relay inside that circuit remains in the “open” state, so no power passes through the gate 4. These “N” side disconnect and synchronization generation sub-circuits 2, 3 provide several functions for the operation of the ATS.

[0080] When the input is not powered, the disconnection from the GK 4 is provided, offering a safe disconnection from the source and providing the disconnection isolation voltage capacity required by various safety agencies (such as Underwriters Laboratories (UL)). The mechanical gap in the relay contacts prevents voltages up to 3000 volts from passing through.

[0081] The commands from the digital control electronics 1 can command the "N" side disconnect and synchronization generation sub-circuit 2, 3 to engage or disengage in case the timing requirements are met.

[0082] The "N" side disconnect and synchronization generation sub-circuit 2, 3 also has a circuit therein for detecting the zero-crossing of the AC voltage when changing from one polarity to the other. The generation of this signal allows the generation of pulses symmetric about the zero-crossing to be formed and sent to the digital control electronics 4 for providing the information required to provide electronic synchronization and control the various actions of the ATS.

[0083] Figure 11 A simplified means of achieving this in the "N" side disconnect and synchronization generation sub-circuit is shown. The circuit 200 is made up of three main elements, namely an input bridge 202, a comparator 203 and an isolated optocoupler 205. When the AC voltage is applied to the input 201, it is rectified in the bridge 202. The rectified voltage is amplified by a resistive divider Rl and R2 to a usable voltage which is applied to the input of the comparator 203. The other input of the comparator 203 has a reference voltage applied formed by a resistive divider R3 and R4 and filtered by a capacitor Cl. When the applied rectified voltage from the AC bridge is greater than the reference voltage, the output of the comparator 203 will "turn on", in this case the output is 5 volts, i.e. high. When the applied rectified voltage from the AC bridge is less than the reference voltage, the output of the comparator 203 will switch to "turn off", in this case the output is 0 volts, i.e. low.

[0084] The synchronization diagram 300 shows the typical voltage-time waveforms of this circuit 200. The AC in 207 is rectified 208 and the output of the comparator produces pulses 209 at the points where the original AC in 207 crosses the threshold plus the threshold of the comparator. These pulses are almost symmetrical to the actual zero-crossings of the original AC input voltage.

[0085] The synchronization pulses formed in the "N" side disconnect and synchronization generation sub-circuit 2, 3 also carry information about the voltage applied to the circuit in the form of the pulse width. As the voltage increases, the pulse width becomes narrower and narrower. This allows the digital control electronics to detect the applied voltage on the same signal path as the synchronization pulses.

[0086] Figure 12It is shown how the sync detector circuit is also used to extract the AC input voltage value at the digital control electronics section. Assume that a high voltage, for example 240 VAC, is represented by the AC in 207 in the sync chart 300. Then the rectified voltage 208 is just crossing the threshold and the resulting pulse 209 is very narrow. However, if a lower voltage, for example 120 VAC, is applied, as shown in the second sync chart 301, the rectified AC voltage 221 crosses the threshold much faster and thus the pulse of the comparator output 222 becomes wider. The digital control electronics can compare the times of the rising and falling edges of these pulses and apply a mathematical formula to retrieve the exact voltage represented by these pulse widths. Alternatively, the digital control electronics can hold a table of representative values that, when compared to the detected pulse width times, can also result in a very accurate representation of the applied voltage.

[0087] The output of the comparator circuit in the "N" side disconnect and sync generation sub-circuit is passed through an opto-isolation circuit to ensure that the digital control electronics are electrically isolated from any AC or DC voltage applied to the input. This is a safety requirement and is enforced by various regulatory bodies such as Underwriters Laboratories (UL).

[0088] Figure 2-AThe principle of the "N" side disconnect and sync generation sub-circuit is shown. The AC filter section 21 shows a simple Pi filter, with the AC mains attached to the electronics of the "N" side disconnect and sync generation sub-circuit via a 250 milliamp (ma) fuse F5. A capacitor and a pair of inductors are used to prevent any high frequency noise generated in the attached circuit 22 from entering the AC mains line. This is done to prevent interference with other external electrical and electronic equipment. This is also necessary for various regulatory agencies, such as the Federal Communications Commission (FCC), among others. The power, after being filtered, is sent to the switch mode current limiter 22, where the AC high voltage is rectified in D2, D3, D8, and D9, and delivered to the filter capacitor C2 via D4. D4 isolates the rectified DC from the bridge from the filtered DC of C2. The unfiltered rectified DC is delivered through a resistive divider R6 and R5 to the comparator for the development of sync and voltage data, as previously described. The rectified and filtered DC voltage of C2 is delivered to the switching chip Q9 via a pair of filter inductors L10 (a ferrite bead for very high frequencies) and L12 (for mid frequency limiting). The switching chip Q9 switches on and off at a rate of approximately 80 Khz, and the duty cycle determines how much current is present in L1. Since this is switching from a single pole source to L1, the flyback energy in L1 is contained by D10. The switching chip Q9 is preset to adjust the duty cycle to maintain a constant current of 20 ma. The chip was originally designed for modern LED lighting, but its purpose is to simplify the power supply design of the present invention. The varying pulse in L1 is converted to a fairly constant current of 20 ma, which is then allowed to pass through the coils of two relays 21, opening the main AC power. The other side of the two relay coils 21 goes into the on-off switch 23 at the drain of Q5. If Q5 is "on", the current is passed to the auxiliary filter capacitor C7 in the sync pulse generator section 25. The 20 ma overcurrent is submitted to the cathode of ZD3, and when the voltage reaches 8.2 volts, the Zener conducts to maintain approximately 8.2 volts. This voltage is submitted to the input of the 5 volt regulator Q7. This is a precision 5 volt linear regulator. As long as the total power requirements of the regulator output and the attached circuit do not exceed 20 ma, then there is sufficient headroom voltage to maintain the precise 5 volt regulation. The design of the sync pulse generator 25 comparator circuit is such that the current required to do the detection function is very small. Only about 2 ma is actually used in this part of the circuit. This leaves 18 ma available. Some of the 18 ma available at the input of the 5 volt regulator Q7 is transferred to the opto-coupler U4 26, and through a 1 K resistor to the output of the comparator U7. If U-7 is in the worst case voltage detection mode, where the output is always "on" (or low), then all 8.2 volts is dropped through the 1 K resistor, minus the 2 volt drop of the LED in the opto-coupler U4. The maximum current resulting from this is 6.2 ma.Thus, in all cases, the total current for the series switch mode regulation is 20 milliamps, which is sufficient to drive all possible circuit combination requirements.

[0089] This approach was chosen to optimize the operational efficiency of the circuit. The wasted power is very small, and the overall circuit power efficiency is approximately 84%. The total quiescent power for operating the "N" side off and sync generation sub-circuit is approximately 0.65 watts. The A side and B side add up to approximately 1.3 watts. This is a very high efficiency for all the functions being implemented.

[0090] This approach also allows the operation of these circuits to function over a range of approximately 30 volts AC up to 300 volts applied to the input. These circuits must function over the maximum AC input voltage range to allow the monitoring and functioning of the ATS regardless of the voltage applied.

[0091] In the event that the controller wishes to turn off the input, a signal "forced off" 27 from the digital control electronics is present. This is done in every transmission cycle to prevent any possible arcing between the contacts of the gate (s) 39 and 40, resulting in a short between the A side and B side power inputs. Figure 3 The "forced off" 27 signal turns on the LED in opto-coupler U1, which in turn shorts the gate of Q5 to the source of Q5. This causes the drain of Q5 to turn off, and the current path to the relay is turned off. Approximately 2 milliseconds later, the relay contacts open, and the power between the input and output of relay 21 is turned off.

[0092] The "forced off" 27 signal turns on the LED in opto-coupler U1, which in turn shorts the gate of Q5 to the source of Q5. This causes the drain of Q5 to turn off, and the current path to the relay is turned off. Approximately 2 milliseconds later, the relay contacts open, and the power between the input and output of relay 21 is turned off.

[0093] When the "forced off" is removed from the opto-coupler U1, and the opto-transistor turns off, then the current from Rl (3.9 Meg ohm resistor) is applied to the gate of Q5, the voltage quickly rises to approximately 10 volts, and the drain of Q5 is connected to the source, Q5 is turned on. Current can now flow through the coil of the switching relay, as previously described, supplied by the switch mode chip Q9. Relay 21 is now energized, and the contacts are turned off approximately 7 to 10 milliseconds later.

[0094] During the presence of the "forced off", no sync pulses are required during the transition process. The voltage and timing have been determined by the digital control electronics. However, the "forced off" is usually only present for approximately 20 milliseconds, which is just enough to complete one transition. During this 20 milliseconds, the power stored in C15 keeps the comparators operating, and the detection of pulses can continue if the information is required.

[0095] Figure 3A detailed block diagram of the input selector or gate keeper (GK) is shown. This is the heart of the ATS. Here, power from either the A-side disconnect switch or the B-side disconnect switch is directed to the output and ultimately to the "load". Its operation is entirely directed by commands from the digital control electronics. When the digital control electronics has no signal, all relays and solid state relays (SSRs) in the GK are in the open, non-conducting state. This presents the "fail safe" condition.

[0096] In order for the digital control electronics to direct power from the A-side disconnect switch output, it must first ensure that no control signal is sent to the B-side diversion circuit. A special piece of code in the digital control electronics performs this check every time it attempts to change the state of either input. It is of utmost importance that the A-side and B-side never be connected to the output at the same time, as this would result in a short circuit between the A-side and B-side inputs and could result in blown fuses and perhaps greater damage. A second layer of protection includes the implementation of a hardware interlock 49 to prevent two commands from occurring at the same time. For example, if the digital control electronics requires the A relay coil driver to turn on by asserting control line 42, this signal will also appear at the input of logic gate 46. Since the true state of the A-side request is inverted at the input of logic gate 46, any signal present at 41, which drives the B-side control line, is blocked by gate 46. Conversely, a signal from the digital control electronics requesting the B-side relay coil driver 41 to turn on is asserted and will appear at the inverted input of logic gate 43, which in turn shields any signal from the A-side digital control electronics command 42 to turn on the A-side relay coil driver. The same concept applies to the IGBT drivers. These functions are similar to the relays, but have almost instantaneous response times. A command to turn on one side or the other will result in a shielding signal being sent to the other side and prevent the double turn on condition from existing. A "high" in the IGBT drive A-side control input 47 will appear as a low to the gate on the B-side 45 and inhibit any signal from the digital control electronics from passing through gate 45. Conversely, a "high" in the IGBT drive B-side control input 48 will appear as a low to the gate on the B-side 44 and inhibit any signal from the digital control electronics from passing through gate 44. A 5KV optical isolator is included between the digital control electronics and the IGBT drivers. This is necessary because the IGBT drivers operate at the AC line voltage potential of their respective AC source. The relay coil drivers do not require isolation, the coils of relays 39, 40 are mechanically isolated from the AC line voltage.

[0097] Figure 3-A A detailed electronic schematic of the input selector or gate keeper (GK) is shown.

[0098] When the digital control electronics determines that the A side AC power should be connected to the output, it asserts both the gate keeper to A (GK to A) signal and the IGBT drive A. The 5 volt logic control signal of the GK to A present will turn on FET Ql 1. Its source is connected to ground, so the drain to ground, thus supplying current to the coils of the A side gate keeper relays, RY 3 and RY 7, which get their coil current from the +12 volt power supply. The magnetic field current starts to build in the coils and the relays start to energize. Generally, these relays take 7 to 10 milliseconds to operate. Generally, the larger the relay, the slower it operates. During this time, the back half of the operation has already started. The digital control electronics also issues an assert command to the IGBT drive A input. This high level (5 volt) signal sends current through resistors 27 and 28 to the LEDs of U13 and U15, 5KV isolated opto-couplers. This current, in turn, turns on Q14, a PNP bipolar transistor. The turn on of Q4 is generally present due to the action of the base pull down resistor R31. If for some reason, the IGBT drive B is high (asserted for some reason), the base of Q14 will also be high and no current will be able to pass through the collector of Q14, thus disabling the IGBT drive A command. The transistor Q14 is essentially the logic gate, Figure 3 discussed earlier, logic gate 44. This is the second layer of fail safe discussed earlier. However, assuming that the IGBT drive B is not asserted and the IGBT drive A is asserted and current is now flowing in U15 and U13, the other side of those opto-couplers will now also conduct.

[0099] To understand how the IGBT driver turns on the IGBT, it must be assumed that the AC power has been present in the A side disconnect switch for at least a short period of time. The AC voltage that has been present has conducted through diodes 13 and 32, and R41 and R3, charging capacitors 26 and 32, each to 20 volts. When these capacitors reach 20 volts, the current is diverted through Zener diodes ZD 5 and ZD 1, and the voltage is held at 20 volts. These capacitors are each 4.7 microfarads. The amount of charge they hold is important in the discussion that follows.

[0100] When the opto-triac in U13 turns on, 20 volts from C26 will conduct through R9 and to the base of Q13 and resistor 2. Capacitor 33 presents a very short impedance to this turn on and filters out transient noise. Otherwise, capacitor 33 does nothing. When the voltage is applied to the base of Q13, the voltage rises very quickly, essentially limited by the charging rate of C33. As the base of Q13 rises, the transistor releases the current path from the emitter to the collector, essentially turning the transistor off. The rising voltage at the base of Q13 is now transferred to the base of IGBT Q2 via diode 21. This rising voltage is now limited by the base capacitance of IGBT Q2 as well as the current limit of the opto-coupler and R33. Since the opto-coupler is about 200 ohms at this point, the rise time is relatively fast, about 150 microseconds. IGBT Q2 is now conducting. Any AC voltage that is present at the contacts of RY7 at this point is shunted through diode bridge BR2 and through the collector-emitter of IGBT Q2. Effectively, the AC input to bridge BR3 is shorted. This entire process takes about 200 microseconds. At the same time, relay 7 has just begun to energize. Another 7 to 10 microseconds elapses before its contacts actually meet each other. The AC input on the load side is now connected.

[0101] The same process also occurs on the other half of the A-side IGBT drive, the side driven by U15. Eventually, IGBT Q3 will be turned on, shunting bridge 3, and delivering AC power to the other side of the A-side path between the A-side disconnect switch to the output and to the load.

[0102] After a period of about 100 milliseconds, assuming the relay has closed and all current is bypassing the IGBTs. The digital control electronics will de-assert the IGBT drive A and IGBT drive B control signals. If for some reason the digital control electronics does not release the drive signals, the design features of the IGBT drivers themselves will release the drive signals from the IGBT gates and turn off the devices. This is accomplished by the decay of the stored charge in C26 and C32 described above. From the current path of C26 and C32, through the opto-coupler and through the 68K base resistors of Q13 and Q21, eventually C26 and C32 will discharge to a point where the IGBTs do not have enough voltage on the gates of these devices to maintain the current flow of Q2 and Q3 collector to emitter. Even if some current is supplied to C26 and C32 from D13 and D32, the 560K and 68K resistor divider, through the half wave rectifier, will not be able to provide enough voltage at the base of the IGBTs to maintain the current flow. When the maximum input voltage to the ATS is 277 volts AC, there will only be about 6 volts on the gates of the IGBTs and the devices will turn off. The careful selection of components makes this function work without the need for any additional circuitry.

[0103] When the digital control electronics determines that it is time to turn off a particular side of the GK, there are two possibilities. One is to turn off immediately, which means that it is turned off as fast as possible due to the voltage loss over the path. This occurs for example when this is the A side, the A side is preferred, and the load has been connected to the A side for some time. This is the normal state.

[0104] When the A input AC voltage is below an acceptable level, the control logic can determine that the A input power is failing, and a power outage is in progress (as opposed to for example a power quality disturbance). It is now necessary to switch to the backup power source (B side in this example) as fast as possible. The first action to consider is that the digital control electronics will start the disconnection process immediately after it has determined that the failure is valid by observing that the sync pulse occurs at a time it should not or that the sync pulse is longer than it should be. It is of utmost importance that the failing AC power input is completely disconnected from the output before the backup power source is connected to the load. Otherwise, current will be diverted from the backup power source to the primary power source, which can have a very low impedance (for example, the entire AC grid). Therefore, it is desirable to know that a few milliseconds have been spent verifying that the failure has occurred, in addition to the two milliseconds (plus a small buffer of 1 millisecond) to ensure that the input relay and the gatekeeper relay have enough time to open mechanically. As mentioned previously, this time is on average around 2 milliseconds. Therefore, the command to "force disconnect" the primary side (A in this example) is issued immediately, and the control lead to the GK to A is also de-asserted. This starts the process of disconnecting from the A side. It is assumed that the IGBT drive to the A side has already been removed, preferably around 200 milliseconds after it was asserted a long time ago when the power was initially switched to the primary side.

[0105] The digital control electronics must now patiently wait for at least two milliseconds. In the currently used relays, the ATS digital control electronics actually waits for 3.5 milliseconds, but this value is programmable in the digital control electronics and can change depending on the relays used in these ATS units. But it waits until it is sure that enough time has passed for the mechanical relays to have opened the path from the previously connected power source and the output. At this point, the digital control electronics can assert the IGBT drive B and the signal to the GK to B, and connect the load to the backup power source as described in the connection sequence above.

[0106] When the IGBTs are driven off and the opto-coupler is not on, there is no current source to keep C33 (C47) charged, and their voltage decays from anywhere until these capacitors are discharged completely via resistors R2 and R4. At this point, the bases of Q13 and Q21 are at the collector potential. Q13 and Q21 are Darlington coupled transistors whose gain characteristics exceed 20,000. Any attempt to raise the voltage on the emitters of these transistors Q13 and Q21 will result in an immediate conduction to the collector potential. In other words, the gates of IGBTs Q2 and Q3 are shorted to their emitters. This is necessary. Because the collectors are connected indirectly to the output of the ATS via bridges BR2 and BR3, when the IGBTs on the standby side turn on and deliver AC to the load from that side, they will turn on quickly. The very high rate of change of voltage that results at the output will be present at the collectors of IGBTs Q2 and Q3, which are now off. Without the very low impedance on the gates of IGBTs Q2 and Q2 to clamp it, the high rate of rise at the collectors will attempt to turn on the IGBTs by capacitive coupling inside the device. The higher the rate of rise of voltage, the more likely the IGBT is to turn on by mistake. Therefore, there is always a clamp between the gates to emitters of the IGBTs when the IGBTs are off. This unique IGBT drive scheme is both simple and stable. It requires no external power to operate. The switching from IGBT drive B and GK to B on the standby side is functionally mirrored on the A side.

[0107] Figure 4 The ATS is shown how it monitors the current and uses the output current to retrieve the data needed for synchronous zero crossing. As an ATS, the decision to transfer the load from one active AC source to another active AC source requires additional considerations beyond performing the transfer as quickly as possible. Since both AC sources are present, additional considerations can be required when deciding when to disconnect from the active source delivering power to the load and then connect to the active AC source that is considered the primary source. This event occurs each time the primary source goes off, the ATS transfers to the standby source, and then eventually the primary AC source is restored. At this time, the transfer that the ATS must make is from one good source to another good source.

[0108] When disconnecting the load from the active AC source, it is necessary for the opening of the relay to occur at or near the zero crossing of the current. This helps to create a strong contact arc and extends the life of the relay contacts. In the ATS described here, the disconnect switch and the disconnect relay in the synchronization section do not have solid state bypass circuits to unload the current from the relay contacts during the disconnect. Therefore, the disconnect must be synchronized with the zero crossing of the current in the circuit.

[0109] The ATS described herein can deliver power to various types of loads. One type of load is a so-called reactive load, which is commonly found to have a combination of capacitance, inductance, or both. When there is capacitance or inductance in a circuit, the voltage and current waveforms are not in sync. There are two components of power flow - one component flows from the source to the load and can do work on the load, and the other component, called "reactive power," is due to the delay between the voltage and current, called the phase angle, and does not do useful work on the load. It can be thought of as current that arrives at the wrong time (too early or too late). This phase difference between the actual voltage zero-crossing and the current zero-crossing requires that, since relay contacts can be damaged by current rather than voltage, it is necessary to have the relay contacts open at the time the current passes zero. Since this can be different from the time the opening switch and the sync section detect a zero-crossing, another method must be used to determine the timing of the relay opening, and must be based on the current, not the voltage present.

[0110] When both sources are present and the transition is about to occur, the digital control electronics must measure the output current and, if it is significant, use it to determine when to open the various relays in the current path. In the ATS described here, the digital control electronics have loaded into its memory at the time of manufacture a table containing the measured time between the command to release a given relay and the successful opening of the contacts. This time is typically about 2 milliseconds, but can vary significantly due to manufacturing variations. Therefore, the digital control electronics record the delay time for each relay in the ATS, and can use this information to calculate the exact time to open when preparing to disconnect a load from the active AC source.

[0111] The digital control electronics also determine the time from one half-cycle to the next by measuring the rising edge to rising edge of the sync pulses generated by the opening switch and sync section. Using this information, the digital control electronics can now subtract the known relay delay from the time between half-cycles and arrive at a number that predicts when the relay contacts will begin to open relative to the zero-crossing of the current. The digital control electronics will prepare to have the relay open, and then at the next zero-crossing of the current, will subtract the amount of time calculated from the relay opening time from the time between half-cycles, and the digital control electronics will issue the opening command.

[0112] In this manner, the ATS described herein can open the load very close to the actual zero crossing of the current by performing these predictive calculations. This minimizes the degradation of the electrical contacts within the relay. In addition, there can be conditions that prevent the relay contacts from releasing when commanded to do so by the digital control electronics. The most common cause is welded contacts, which are the result of some excessive current during a previous transition. Other cases can include mechanical wear or material degradation due to time, heat, or other causes. In any case where the contacts are not operating as expected by the digital control electronics, a method is described herein that allows the digital control electronics to detect this fault condition. If the fault condition is detected before any additional relay or SSR actions are commanded, then a short circuit of the A-side power to the B-side power can be avoided. In many large automatic transfer switch applications, the traditional ATS design is accomplished by mechanically connecting the power contacts of the relay to a set of auxiliary contacts that can be monitored by the digital control electronics for this authentication process. In the case of the MINI ATS application described herein, physical size is an important issue. A new method of detecting relay operation is described herein, called the relay operation authentication detector, which allows this authentication while maintaining a small form factor. In addition, this detection means is directly related to the active electrical conducting portion of the relay that actually carries the power through the relay. By detecting this specific electrical conductor, the status of the contacts, whether connected to power or not, can be positively confirmed. This authentication feature allows the digital control electronics to immediately check the results of the action request when it commands the closing of a required relay or the opening of a required relay and verify that it has been completed before proceeding to perform any other actions. In the case where the relay in question fails to complete the instruction, the digital control electronics can go through a process of stopping any additional actions, reporting the failure event to the supervisory controller, and it can make multiple attempts to operate the relay and possibly self-repair the electrical fault by opening a potentially welded contact. In this case, the digital control electronics can choose to have the entire MINI ATS return to operation or place it in a safe state, such as a complete shutdown. The determination of how to handle the fault condition is fully programmable and can be tailored to various applications. This flexibility provided by implementing authentication is unique in an automatic transfer switch.

[0113] In addition, the authentication circuit allows the digital control electronics to operate in a mode where the next step is not determined by time as described above, but by what state the individual components are in physically or electrically. For example, when a command is issued to disconnect a relay from a source, the digital control electronics does not calculate when it should disconnect to allow continuation, but simply waits for an authentication signal from the affected relay indicating the action was successfully completed. The digital control electronics simply sets a time limit on this basis so that a detection of a fault can be determined. But as a state control process, it means that the next action dependent on the impending state change is timed to be at the optimum time for the next action to be undertaken.

[0114] Figure 4 The basic electrical and electronic components of the current sensing portion of the ATS are shown. The main sensing element is a Hall effect sensor 51 which is adjacent to the hot output lead attached to the ATS output. The magnetic field created by the passing current 57 is detected in the Hall effect sensor 51 and amplified. Zero point restoration 52 of the sensed signal is necessary to stabilize the conversion from AC measurement to DC in the precision rectifier 52. After the current waveform is rectified, it still returns to zero every half cycle. At the instant it returns to zero, the zero crossing detector 55 outputs an assertion. This signal is sent to the digital control electronics for calculation of timing. In addition, the rectified output of the precision rectifier 52 is also sent to an integrator which is comprised of an array of capacitance and resistance which can smooth the sensed current and convert it to a smoothed DC level. This DC level is then sent to the digital control electronics via a buffer amplifier and through an integrated analog to digital converter into the digital control electronics for digital processing and reporting of the current level to the communications port and ultimately to the remote monitoring device.

[0115] The integrated DC level is also used by the digital control electronics to determine if the ATS should turn on the light for the "acceptable maximum load" warning. A feature of the ATS described here is that it is able to set the warning light when the load exceeds a preprogrammed level.

[0116] Another action that the digital control electronics can take using the integrated DC level is to shut down the output in the event of an overload. If the current exceeds a preprogrammed level, the ATS can very quickly de-energize the gate relay to protect the AC power circuit. The digital control electronics can then turn on another warning light to indicate that an overload has occurred and it can send status data to the remote monitoring device through the communications port.

[0117] Another feature of the ATS described here is that it is able to set the warning light and coincidentally shut off power to the load when the load exceeds a preprogrammed level.

[0118] A reset button is provided Figure 8 , 9 , 10, item 104) as a means for the operator to reset the load-fault condition after the fault has been removed.

[0119] The unique filtering at the hardware level in the integrator 54 and the software calculations of the digital control electronics allow for the precise emulation of any desired fuse curve or any desired circuit breaker.

[0120] The output current sensing, as determined by the digital control electronics, can also be used to operate the cooling fans predictively. Rather than waiting until the internal of the ATS warms up due to a heavy load detected in the current sensor 11, and then turning on the fans, the digital control electronics can predict the internal heating due to the load detected in the current sensor 11. Thus, the fans are turned on before the individual components heat up. This functionality can be useful in improving the reliability of the ATS.

[0121] The ATS can predict the internal heating and proactively start the fan(s) to reduce material fatigue and improve reliability.

[0122] Figure 5 An overview of the indicators 9 and the communications port 10 in the ATS is shown.

[0123] These indicators are general purpose LEDs of various colors. With the use of state-of-the-art components, bright and efficient LEDs provide excellent indication of the various states of the ATS described herein. A unique castellated lens assembly allows for efficient airflow, as well as an excellent viewing angle range of the LEDs.

[0124] In addition, a current limiter 60 is in the power supply path of all the LEDs. This prevents the power supply from being overloaded in the event that 3 or more LEDs are illuminated at the same time.

[0125] The communications portal 10 provides a dedicated communications setup between the digital control electronics and the remote monitoring and control electronics.

[0126] This port provides three functions, but other functions can also be implemented.

[0127] i. USB communication with the remote monitoring and control electronics.

[0128] ii. Connection between the peripheral interface controller (PIC) (a type of MCU) inside the ATS described herein and external programming tools. This allows for the updating of the software (firmware) of the PIC without having to open the enclosure. There can be customers that own the ATS described herein that require special functionality. Due to the unique design of this ATS, these customer requirements can be met by providing specialized operating code to the digital control electronics of the ATS.

[0129] iii. The connection between the digital control electronics and the external communication interface converter allows for long line communication with the remote monitoring and control electronics. USB has a short length limit and therefore can not be suitable for all communication requirements.

[0130] The digital control electronics can send data to the remote monitoring and control electronics via USB through the USB Type-C connector 72 accessed through the panel via the USB 2.0 interface converter 71. The USB Type-C connector is chosen because it has a unique pinout that generally allows the connector to be mated in either polarity. The pins on one side of the connector are mirrored to the pins on the other side, so no matter how the mated connectors are inserted, the communication and voltage sent through the connector system will be preserved. The ATS described here takes advantage of this bipolarity for added features. By flipping the connector, this flip can be detected and an alarm signal 76 sent to the digital control electronics via the polarity detection circuit 70. The polarity detection circuit operates by detecting whether one of the pins has a ground pin present. Instead, the complementary pin (in the opposite condition of the mated connector) is connected to the +5 volt pin of the connector. In this way, the orientation of the connector can be determined by the digital control electronics. This is useful by allowing the digital control electronics to determine whether it should communicate via USB or whether it should be prepared to accept data from a remote programming tool. This feature can also be used to alarm the operator that the connector is flipped. This can be used to help improve the security of the data contained in the digital control electronics. By flipping the connector to one orientation, a physical barrier is provided to writing data into the digital control electronics. However, by flipping the connector to the other orientation, data can be written into the digital control electronics while the digital control electronics can provide a unique illumination to the LEDs to alarm the operator of this write vulnerability.

[0131] Therefore, the unique wiring of the USB Type-C connector allows the ATS described here to communicate with multiple types of external electronics and improve the security of the data stored in the ATS.

[0132] Figure 6An overview of the power supply system in the ATS described herein is shown. Since it is not known at any time whether power will be present on the A input, the B input, or both, a power supply system including 5KV isolated from the digital control electronics is included, but it can be obtained from both the A and B inputs. A 12 volt DC supply is attached to the output of the A side disconnect and sync AC power output. Also, a 12 volt DC supply is attached to the output of the B side disconnect and sync AC power output. Each of these power supplies is connected to a common +12 bus via isolated diodes 86 within the power supply module. These diodes provide the ability for either power supply to operate in the event of a failure of one or the other power supply. This is a redundant power supply system and is an added feature of the ATS described herein.

[0133] The 12 volt bus is distributed to various electronics on the digital control electronics 1 and the A or B side selector 4 electronics, where local regulator chips are used to reduce the 12 volt DC power to 5 volts and 3.3 volts if needed. The input to the 12 volt power supply is protected by fuses 89, 90 for safety reasons.

[0134] In addition to the local ATS power supply, an auxiliary power supply 81 is provided for delivering power to the USB port 91. This is a 5 volt 2 amp supply, also an isolated rated supply, to supply power to USB client devices according to regulatory agency requirements such as Underwriters Laboratories (UL) and other similar regulatory agencies.

[0135] The input to the USB power supply 81 is supplied via the selector relay 88. Each of the inputs to the selector relay has a single fuse in lines 84, 85 to protect the 5 volt power supply 81 and prevent a shorted path through the relay that could occur between the A side and the B side in the event of a catastrophic failure of the selector 81.

[0136] Figure 8 、 Figure 9 and Figure 10 Various examples 100 of the ATS described herein are shown.

[0137] Figure 8 Variants are shown with flexible electrical cord 106 into the ATS 100 described herein and flexible electrical cord 109 out of the ATS 100 described herein. This is a 30 amp or 32 amp model, but other current handling capability electrical cords can be readily applied. Various amp capacity models only differ in the electrical cord, the connectors on the ends of the electrical cord, the internal main fuse rating, and the preprogrammed information contained in the memory of the digital control electronics. The voltage range selection is automatic in the main unit 100, but is primarily determined by the type of plug installed.

[0138] The output cord 109 of the ATS 100 described herein exits the end cap 101 through a stress relief sleeve 102 that can be selected according to the cable size without the need to change the size of the hole in the end cap. This reduces manufacturing costs.

[0139] The output end cap 101 also has Figure 5 - the portal 103 for communication described in -72. The end cap 101 also contains a push button 104 for resetting the ATS electronic circuit breaker or selecting the preferred input.

[0140] Figure 9 A variation is shown with a flexible cord 106 entering the ATS 100 described herein and a pair of IEC type C19 receptacles installed in the end cap 101 of the ATS 100 described herein. This is a 30 amp or 32 amp model. The amp capacity model only differs in the specifications related to the assigned country of use, the internal main fuse rating and the preprogrammed information contained in the memory of the digital control electronics. The voltage range selection is automatic in the main unit 100.

[0141] The dual IEC type C19 connectors of the ATS 100 described herein are installed directly in the end cap 101.

[0142] The output end cap 101 also has Figure 5 - the portal 103 for communication described in -72. The end cap 101 also contains a push button 104 for resetting the ATS electronic circuit breaker or selecting the preferred input.

[0143] Figure 10 A variation is shown with a pair of IEC type C20 panel mount plugs 121 at the entrance of the ATS 100 described herein. A single IEC type C19 receptacle 120 is installed in the end cap 101 of the ATS 100 described herein. This is a 16 amp model. The voltage range selection is automatic in the main unit 100.

[0144] The output end cap 101 also has Figure 5 - the portal 103 for communication described in -72. The end cap 101 also contains a push button 104 for resetting the ATS electronic circuit breaker or selecting the preferred input.

[0145] Figure 13 A cross sectional end view of the extruded enclosure 201 of the ATS described herein is shown.

[0146] The enclosure has many features including:

[0147] i. extruded aluminum for strength and durability

[0148] ii. all metal construction minimizes electrical and magnetic interference problems

[0149] iii. Slots on each side of the enclosure, with sufficient surface area for heat dissipation

[0150] iv. Slots on each side for mounting.

[0151] The slots on the sides are configured as "T" slots, which means that the back of the slot has a small groove that facilitates mounting with various hardware. The dimensions and shape of these "T" slots are optimized for the use of off-the-shelf mounting hardware. In general, "T" slots are very common, but in this instance, the slots have additional features that make them unique.

[0152] The slots are extruded the entire length of the enclosure. This allows mounting fasteners to be inserted from either end and positioned laterally along the length of the ATS for easy positioning of adjacent holes, such as computer racks, clip fittings, flexible hinges, etc. In addition, the slots are spaced from each other such that standard off-the-shelf DIN rails can be inserted directly.

[0153] In addition, each slot also has a rib along the centerline 212 that functions to engage with the slot in standard round and flat head screws.

[0154] In addition, the slots have a clearance groove 213 in each side of the slot that facilitates standard off-the-shelf flat washers when the fastener hardware has different sized head flange widths.

[0155] In addition, the dimensions of each side of the slot are such that they are only slightly wider than standard off-the-shelf hex nuts that fit to the dimensions of a data center rack.

[0156] Some of the types of fasteners that this improved "T" slot system can accommodate are listed below (but are not limited to):

[0157] - #10 X 32 Hex Head Bolt 202

[0158] - #10 X 24 Hex Head Bolt 202

[0159] - M5 X.8 mm Metric Hex Head Bolt 202

[0160] - #8 X 24 Hex Head Bolt 202

[0161] - #8 X 32 Carriage Head Bolt 203

[0162] - #8 X 32 Standard Round Head Bolt with Washer 204

[0163] - #10 X 24 Standard Round Head Screw without Washer 204

[0164] - Hex Nuts, #8 and #10 205, 206

[0165] #8 X 32 flat head screws and washers 207

[0166] #8 and #10 hex or spline socket head screws (non-standard) 209

[0167] #8 and #10 Allen socket head screws (non-standard) 210

[0168] #8 and #10 slotted head screws 211

[0169] With the ability to utilize a variety of mounting hardware styles, along with slots that are full length of the enclosure, and included ribs that prevent round and flat head screws from turning in the slots, the installation of this product is versatile and convenient.

[0170] Figure 14 One relay contact operation verification 400 is shown that includes the general major components of the relay operation verification detector portion of the MINI ATS.

[0171] AC power 212 is always present on the armature of the relay 211. When a command from the digital control electronics is initiated through the GK relay control 210, the relay 211 will move the armature to the switched high voltage output leg 213 of the relay 211. This is the normal power path for the relay switch operation. There are four such switches in the mini ATS, including the A side hot and neutral (or auxiliary hot) and the B side hot and neutral (or auxiliary hot) switching.

[0172] The relay contact verification circuit is made up of a very small pulse transformer 214, designed to operate at low voltages such as 5 volts, connected across the armature of the relay 211 and the unused normally closed contact 217 of the relay 211. The winding 216 of the pulse transformer 214 is thus normally shorted by its normally closed position when the relay 211 is not operating, and no power is sent through the relay from the input 212 to the output 213.

[0173] At all times, a small 400 kilohertz (KHz) oscillator 215 is operating. This frequency can be any frequency that suits the characteristics of the selected pulse transformer 214, and can vary from application to application. For use in the MINI ATS, a transformer that operates well at 400 KHz was selected due to its small size and efficiency. The output of the oscillator 215 is connected to the pulse transformer 214 through a current limiting resistor 220. Thus, when a set of windings 216 is shorted due to the position of the contacts of the relay 211, the windings on the oscillator connected side of the transformer 219 are also shorted. The majority of the output power of the oscillator 215 is dissipated in the current limiting resistor 220. Subsequently, the windings of the pulse transformer 218 connected to the bridge rectifier 221 also transmit very little signal there. Thus, no voltage is developed across the capacitor 222 and bleeder resistor 223. The voltage output at 224 is essentially zero. Thus, a zero output voltage represents the relay 211 contacts in an open condition with respect to the power path.

[0174] When the command from the digital control electronics is initiated through the GK relay control 210, the relay 211 will move the armature to the switched high voltage output leg 213 of the relay 211, and thus remove the shorted condition on the windings of the transformer 216 at the instant the armature of the relay 211 leaves the contact 217 when the relay coil is energized. When the shorted condition on the windings 216 is removed, the oscillator 215 output can now energize the input windings of the pulse transformer 219, and 400 KHz will be transmitted through the pulse transformer 214 to the output windings 218. The AC will be rectified in the bridge rectifier 221 and filtered by the capacitor 222. Thus, the output voltage indicates that the relay 211 contacts are moving toward or in a closed condition with respect to the power path, and allow the relay to pass power from the input 212 to the output 213. The selection of the winding ratio and the operating voltage of the oscillator 215 determine the output voltage of the bridge rectifier 221. In this example, the output voltage selected is 5 volts, and is directly compatible with the electronics in the digital control electronics.

[0175] The bleeder resistor 223 is connected across the filter capacitor 222 to bleed off the voltage there in the event that the output of the pulse transformer 214 stops delivering voltage due to a shorted condition returning to the closed relay 211 contacts to the normally closed contacts 217. This bleeder is very fast, as the filter capacitor is only required to be large enough to ensure a consistent output voltage during the transition of the output of the transformer 214 from positive to negative.

[0176] When a command from the digital control electronics to disconnect the AC power path through relay 211 occurs, the relay armature transitions from the normally open contact position 213 to the normally closed contact 217. In order for the pulse transformer relay switch position sense winding 216 to short-circuit, and thus signal successful completion of opening the power path, the armature must be physically disconnected from the output. This increases the reliability of accurately detecting the relay state.

[0177] Furthermore, because the transformer is connected only to the unused normally closed contacts 217, the circuit can operate efficiently and autonomously regardless of the voltage or frequency present in the power path.

[0178] FIG15 now shows a basic block diagram of the mini-ATS, including relay operation authentication detectors 301, 302, 303, and 304. It shows a device with no input to output connections, such as the off condition of the mini-ATS. Note that no power path is shown from any input to output connection. Also note that the output of each relay operation authentication detector is represented by L for low, or there is no voltage from the detector within each relay operation authentication detector section. Each of the four relay operation authentication detectors is now in a normally closed position (non-energized) state, and therefore the contact sensing windings of all four relays are short-circuited.

[0179] In normal operation, one or the other of the inputs will be connected to the output. Figure 15b As shown, in this case, input "A" is connected to output "OUT." Each output of the relay operation verification detectors associated with "A" sides 301 and 302 now outputs a high signal, each represented by an H. This high signal is sent to the digital control electronics, where it verifies the relay's state and allows normal operation to continue. In this way, every state change commanded by the digital control electronics can be monitored and verified by the digital control electronics.

[0180] Figure 15c A possible fault condition is shown in which the digital control electronics, via gate amplifier 91, commands the A-side gate relay to open by shutting off power to the relay. However, the normally open contacts on the hot side are shown as "stuck" to the output connection. The complementary relay has already successfully opened. Therefore, the output of the relay operation verification detector from that relay contact remains in a "high" state, signaling to the digital control electronics that the operation to open that relay contact has failed. This allows the digital control electronics to take appropriate steps to not apply power to the gate amplifier on side B, potentially causing a dangerous short circuit from side A to side B.

[0181] Now, the digital control electronics have the ability to repeatedly turn on and off the affected relay and monitor the status of the relay operation verification detector. The repeated operation of the relay has the potential, and possibly the eventual result, of causing the sticking contacts to fall out. With this design's self-healing potential, the reliability of the unit is increased.

[0182] Figure 16 Several methods of improving SBC module uptime and maintainability are shown, which module is used as a control module, either standalone or as part of a larger device. Several ATS examples described herein can be used to eliminate power-related downtime. It allows a single power supply SBC module and other critical loads to be fed by both filtered mains line power and a UPS, or two UPS units, one as the primary power source or as a backup power source. If possible, the UPS can be plugged into the same circuit as the μATS TM A second input different branch circuit allows the UPS to be taken out of service for maintenance or testing without requiring SBC downtime. In this configuration, both the utility line power and the UPS must fail simultaneously to result in downtime. The following figure compares the traditional method of powering an SBC module and the possible method using an appropriate ATS.

[0183] Figure 16 Possible examples of novel methods of activating the surge limiting function are described, which can be used in an ATS unit, as described in this document or other possible ATS examples.

[0184] The subassembly 500 consists of a relay 506 located in the AC power path away from the ATS. The power delivered to the output of the uATS or industrial uATS must pass through this relay. A low value resistor 512, approximately 10 ohms, is connected across the input 505 and output 507 of the relay 506. This resistor can be fixed or of the negative temperature coefficient (NTC) type specifically for surge applications. In the Zonit uATS and Zonit Industrial products, this resistor is of the NTC type and is 10 ohms.

[0185] Since the intent of a surge limiter is to limit peak current at the moment of a source-to-source transition, then become transparent, the circuit relies on the electronic drive circuit in these products to change the state of the relay that directs power within the ATS. The signal to the gatekeeper relay within the ATS can be used to signal this surge limiter circuit to operate. When shifting to the backup power source in the ATS, a 12 to 48 volt drive signal is applied to the diverter relay, called the gatekeeper or GK relay. When shifting back, the signal to the GK relay is removed and then the relay connects AC power to the original source. In other words, the drive to the GK relay internally within the ATS product can be used to operate this surge limiter circuit 500 for both transitions. At the moment of transition, in either direction of the ATS product, this surge limiter circuit will momentarily operate its relay 506, bypassing the AC source through the limiting resistor 512. After a short time, 20 to 100 milliseconds in the uATS and uATS Industrial products, the relay 506 is de-energized and the normally closed (NC) contact again passes power from the input 505 to the output 507, bypassing the internal limiting resistor 512.

[0186] The signal from the ATS product to operate the GK relay is directed from connection 514 through limiting resistor 501 and capacitor 502 to the three transistors 508, 509 and 515 to the input of the surge limiter circuit. If the transition is forward, the current is directed to the base of Q508 and blocked by the reverse emitter of Q509. In this case, Q508 is turned on for a period of time determined by the discharge rate of capacitor 502 and the limiting current of resistor 501. These components are selected to provide sufficient turn on current in Q508 for a period of about 30 milliseconds before the capacitor is sufficiently charged to stop providing current to the base of Q508, causing it to turn off. While Q508 is in the on condition, the collector of Q508 is pulled to the emitter voltage, which can be said to be on. The low going pulse on the collector of transistor 508 is coupled through coupling capacitor 504 to relay 506 coil 511, causing the relay to turn on and operate the armature of relay 506, breaking the short across surge limiting resistor 512. Now, AC power must pass from the input of the surge limiter circuit 505 through the surge limiting resistor 512 to the output 507. After a period of about 30 milliseconds, the charge stored in coupling capacitor 504 is nearly depleted, but at this time the drive signal from transistor 508 is turned off, releasing the drive to relay 506. At this time, the coupling capacitor is discharged and now begins to recharge from the internal DC power supply located in the main ATS unit through the charge limiter resistor 503. This method of powering the relay is novel in that it stores only enough energy to operate the relay for the period of time required, in this case about 30 milliseconds. Also, this configuration takes advantage of the fact that after a transition, the main ATS device will pause for at least about 3 to 5 seconds before initiating another transition. This allows the coupling capacitor sufficient time to slowly charge in preparation for the next interrupt cycle. This places very little drain on the main power supply of the ATS itself. These power supplies are designed to operate at the minimum power demand of the main ATS product, not designed to directly drive additional relays. Utilizing the novel power circuit of the present invention would place excessive power drain on the main power supply and could affect the normal operation of the ATS. This design allows the circuit to be added to existing designs with little modification to those products, except for tapping the GK relay drive for the signal, connecting to the power supply and inserting relay 506 and resistor 512 in the power path away from the ATS device.

[0187] When the input signal to surge limiter circuit 500 goes from a high state to a low state, as in the case of a primary ATS unit switching back to the original source, the falling voltage at the surge limiter input is coupled to three transistors 508, 509, and 515 via connection 514, through current-limiting resistor 510, and coupling capacitor 502. In this case, the falling signal attempts to go negative and is blocked by the reverse-biased base of transistor 508, completely shutting it off. Now, the negative-going pulse from coupling capacitor 502 is caused to conduct forward through the emitter of negative transition detection transistor 509, which is grounded from its base. At this point, the negative transition detection transistor turns on, and its collector is pulled to ground. This is connected to the base of relay driver transistor 2 515, which is configured as an emitter-follower current amplifier connected to coupling capacitor 504. Similarly, as in the reverse case, the current through transistor 515 operates the armature of relay 506 and opens the short circuit across surge limiting resistor 512. AC power must now be passed from the input of the surge limiter circuit 505 to the output 507 via the surge limiting resistor 512. After a period of approximately 30 milliseconds, the charge stored in the coupling capacitor 504 is nearly depleted, but at this point the drive signal from the negative transition detection transistor 509 is turned off, releasing the drive to the relay 506. At this point, the coupling capacitor is discharged and now begins to charge from the internal DC power supply located in the main ATS unit through the charge limiter resistor 503 in preparation for the next interrupt cycle.

[0188] Figure 17 An example of a high-definition (HD) waveform sensor circuit is shown. Key design constraints are small size, low power consumption, and very low cost, which is novel because it enables very widespread deployment of large numbers of HD waveform sensors, and the collection and analysis of this information. This, in turn, enables many types of condition, diagnostic, and predictive analytics for power distribution systems and connected devices, many of which are described in detail in Zonit. The inventions described in Zonit (e.g., power signal signature recognition) can incorporate this high-definition sensor capability to detect and report high-resolution (e.g., 0-100 kHz sampling rate, noting that zero Hz is DC power) waveform samples to measure power quality parameters, such as voltage and current information about the AC power line to which various devices are connected, both at the input and output. It can also be incorporated into any of the Zonit inventions mentioned herein, or implemented as a plug-in module or other convenient form factor (many of which are described herein), and include provisions for storing and / or communicating waveform information to other devices via various communication methods (such as wireless, USB, Ethernet, and others). These requirements have led to the creation of a specialized set of circuits to perform the required functions.

[0189] For safety reasons, the measurement of these AC lines requires very high voltage isolation from the digital and analog circuitry. Isolation of over 3000V AC is typically required. In addition, small size and efficient operation are important in the Zonit product. The high isolation buffer / amplifier shown in FIG. 600 includes an AC power path through a buffer consisting of AC lines in 601 to AC line output 619 via a Hall effect current sense chip 615.

[0190] AC power is also typically supplied to a power supply 605 which generates a DC output isolated from the AC mains power supply. This DC output drives the output amplifier connected to the external digital and analog sub-circuitry. The isolated DC output 603 is also routed to another high isolation power supply 607 which in turn supplies the input to the voltage buffer 613 to allow a DC input referenced to AC line 620.

[0191] For voltage detection, the AC lines 601 are connected to a precision rectifier 608 to generate a rectified DC output without filtering for detection. The output of the rectifier is referenced to AC line 620. The input to the high isolation buffer amplifier 613 is referenced to the same AC line 620. The input 612 of the high isolation buffer amplifier 613 detects the output of the voltage dividing resistors 610 and 611. The high isolation buffer amplifier 613 then outputs a rectified and scaled sense voltage output 617 to the external measurement electronics.

[0192] For current detection, the AC current passes through the input 616 of a Hall effect current sense chip 615 where a weak magnetic field 614 is detected across a high isolation voltage barrier. The sensed current output 618 of the Hall effect magnetic detector 616 is routed to the external measurement electronics. Figure 18 A perspective view of one possible example of Zonit μATS-INDUSTRIAL is shown. The same form factor can be used for Zonit μATS-V2 or other ATS examples.

[0193] The foregoing description of the application has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the application to the forms disclosed herein. Therefore, many modifications and variations are possible in light of the above teachings and the knowledge of the skilled artisan. The implementations described above are intended to explain the best mode presently known of practicing the application and to enable others skilled in the art to utilize the application in such or other implementations and with various modifications as are suited to the particular use or uses for which the original application was intended. The accompanying claims are intended to cover all such alternatives, modifications and variations as falling within the scope of the application.

Claims

1. An automatic transfer switch comprising: a first electrical input for receiving power from a first power source; a second electrical input for receiving power from a second power source; an electrical output for outputting electrical power to one or more electrical devices; a power sensing and conversion module for monitoring power delivered by at least one of the first electrical input and the second electrical input and selectively coupling the electrical output to one of the first electrical input and the second electrical input based on the monitoring; as well as a preferred source selector configured to be capable of selecting one of the first electrical input and the second electrical input as a preferred input to be connected to the electrical output under a default condition, wherein when a signal quality of the preferred input is acceptable, the preferred input is coupled to the electrical output, and when the signal quality of the preferred input is unacceptable, the other of the first electrical input and the second electrical input is a non-preferred input and coupled to the electrical output, the preferred source selector being operable to perform the selection of the preferred input by one of automatic selection based on a comparison of power signals provided by the first power source and the second power source and remote control, such that the selection of the preferred input can be performed without physically accessing the automatic transfer switch.

2. The automatic transfer switch according to claim 1, wherein: The power sensing and conversion module is operable to switch between the first electrical input and the second electrical input based on a quality of a power signal delivered via one of the first electrical input and the second electrical input.

3. The automatic transfer switch according to claim 1, wherein: The power sensing and conversion module is operable to monitor the power signals delivered via the first and second electrical inputs and connect one of the first and second electrical inputs to the electrical output based on the monitored power signals.

4. The automatic transfer switch according to claim 1, wherein: The preferred source selector selects the preferred input based on user input.

5. The automatic transfer switch according to claim 1, wherein: The preferred source selector selects the preferred input based on a comparison of power signals delivered via the first electrical input and the second electrical input.

6. The automatic transfer switch according to claim 1, wherein: The power sensing and conversion module includes a first relay between the first electrical input and the electrical output, and a first solid-state switch between the first electrical input and the electrical output, each of the first relay and the first solid-state switch being operable to cycle the first electrical input and the electrical output to at least one of: connect and disconnect.

7. The automatic transfer switch according to claim 6, wherein: The power sensing and conversion module includes a second relay between the second electrical input and the electrical output, and a second solid-state switch between the second electrical input and the electrical output, each of the second relay and the second solid-state switch being operable to cycle the second electrical input and the electrical output.

8. The automatic transfer switch according to claim 6, wherein: The solid-state switch is operable to selectively cycle at or near a zero crossing of the power signal.

9. The automatic transfer switch of claim 1, further comprising a power control for controlling the delivery of power to the first electrical device based at least in part on an input separate from the power signals delivered via the first and second electrical inputs.

10. The automatic transfer switch according to claim 9, wherein: The input includes user input.

11. The automatic transfer switch according to claim 9, wherein: The input includes environmental input from an environmental sensor.

12. The automatic transfer switch according to claim 9, wherein: The input is a processor input from a processor operable to compare a parameter related to the first electrical device to a threshold value.

13. The automatic transfer switch of claim 1, further comprising a communication input for receiving an input communication signal for controlling operation of the automatic transfer switch.

14. The automatic transfer switch of claim 1, further comprising a communication output for transmitting an output communication signal to a remote processing platform.

15. The automatic transfer switch according to claim 14, wherein: The outgoing communication signal includes information regarding a status of one of: the automatic transfer switch and a connected piece of electrical equipment.

16. The automatic transfer switch of claim 1, further comprising a warning indication for providing an indication when the monitored power reaches a predetermined state.

17. An automatic transfer switch comprising: a first electrical input for receiving power from a first power source; a second electrical input for receiving power from a second power source; an electrical output for outputting electrical power to one or more electrical devices; a preferred source selector for selecting one of the first electrical input and the second electrical input as a preferred input to be connected to the electrical output under a default condition, wherein when a signal quality of the preferred input is acceptable, the preferred input is coupled to the electrical output, and when the signal quality of the preferred input is unacceptable, the other of the first electrical input and the second electrical input is a non-preferred input and coupled to the electrical output, the preferred source selector being operable to perform the selection of the preferred input by one of automatic selection based on a comparison of power signals provided by the first power source and the second power source and remote control, such that the selection of the preferred input can be performed without physically accessing the automatic transfer switch; a power sensing and conversion module for monitoring power delivered by at least one of the first electrical input and the second electrical input and selectively coupling the electrical output to one of the first electrical input and the second electrical input based on the monitoring; as well as Wherein, the power sensing and conversion module includes a first relay between the first electrical input and the electrical output, and a first solid-state switch between the first electrical input and the electrical output, each of the first relay and the first solid-state switch being operable to cycle the first electrical input and the electrical output to at least one of: connect and disconnect.

18. The automatic transfer switch according to claim 17, wherein: The power sensing and conversion module is operable to switch between the first electrical input and the second electrical input based on a quality of a power signal delivered via one of the first electrical input and the second electrical input.

19. The automatic transfer switch according to claim 17, wherein: The power sensing and conversion module is operable to monitor the power signals delivered via the first and second electrical inputs and connect one of the first and second electrical inputs to the electrical output based on the monitored power signals.

20. The automatic transfer switch of claim 17, wherein: The preferred source selector selects the preferred input based on user input.

21. The automatic transfer switch of claim 17, wherein: The preferred source selector selects the preferred input based on a comparison of power signals delivered via the first electrical input and the second electrical input.

22. The automatic transfer switch of claim 17, wherein: The power sensing and conversion module includes a second relay between the second electrical input and the electrical output, and a second solid-state switch between the second electrical input and the electrical output, each of the second relay and the second solid-state switch being operable to cycle the second electrical input and the electrical output.

23. The automatic transfer switch of claim 17, wherein: The solid-state switch is operable to selectively cycle at or near a zero crossing of the power signal.

24. The automatic transfer switch of claim 17, further comprising a power control for controlling the delivery of power to the first electrical device based at least in part on an input separate from the power signals delivered via the first and second electrical inputs.

25. The automatic transfer switch of claim 24, wherein: The input includes user input.

26. The automatic transfer switch of claim 24, wherein: The input includes environmental input from an environmental sensor.

27. The automatic transfer switch of claim 24, wherein: The input is a processor input from a processor operable to compare a parameter related to the first electrical device to a threshold value.

28. The automatic transfer switch of claim 17, further comprising a communication input for receiving an input communication signal for controlling operation of the automatic transfer switch.

29. The automatic transfer switch of claim 17, further comprising a communication output for transmitting an output communication signal to a remote processing platform.

30. The automatic transfer switch of claim 29, wherein: The outgoing communication signal includes information regarding a status of one of: the automatic transfer switch and a connected piece of electrical equipment.

31. The automatic transfer switch of claim 17, further comprising a warning indicator for providing an indication when the monitored power reaches a predetermined state.

32. A method for delivering power to an electrical device, comprising: An automatic transfer switch is provided, the automatic transfer switch comprising: a first electrical input for receiving power from a first power source; a second electrical input for receiving power from a second power source; an electrical output for outputting power to one or more electrical devices; and a power sensing and conversion module for monitoring power delivered by at least one of the first electrical input and the second electrical input and selectively coupling the electrical output to one of the first electrical input and the second electrical input based on the monitoring; selecting one of the first and second electrical inputs as a preferred input to be connected to the electrical output under a default condition, wherein when a signal quality of the preferred input is acceptable, the preferred input is coupled to the electrical output, and when the signal quality of the preferred input is unacceptable, the other of the first and second electrical inputs is a non-preferred input and coupled to the electrical output; and The preferred input is changed to the other of the first electrical input and the second electrical input, the changing being one of automatic selection and remote control based on a comparison of power signals provided by the first power source and the second power source, such that the changing of the preferred input can be performed without physically accessing the automatic transfer switch.

33. The method of claim 32, further comprising operating the power sensing and conversion module to switch between the first electrical input and the second electrical input based on a quality of a power signal delivered via one of the first electrical input and the second electrical input.

34. The method of claim 32, further comprising operating the power sensing and conversion module to monitor the power signals delivered via the first electrical input and the second electrical input, and connecting one of the first electrical input and the second electrical input to the electrical output based on the monitored power signals.

35. The method of claim 32, further comprising operating a preferred source selector to select the preferred input based on user input.

36. The method of claim 32, further comprising operating a preferred source selector to select the preferred input based on a comparison of power signals delivered via the first electrical input and the second electrical input.

37. The method of claim 32, wherein: The power sensing and conversion module includes a first relay between the first electrical input and the electrical output, and a first solid-state switch between the first electrical input and the electrical output, and the method further includes operating each of the first relay and the first solid-state switch to cycle the first electrical input and the electrical output to at least one of: connect and disconnect.

38. The method of claim 37, wherein: The power sensing and conversion module includes a second relay between the second electrical input and the electrical output, and a second solid-state switch between the second electrical input and the electrical output, and the method further includes operating each of the second relay and the second solid-state switch to cycle the second electrical input and the electrical output.

39. The method of claim 37, further comprising selectively cycling the solid-state switch at or near a zero crossing of the power signal.

40. The method of claim 32, further comprising controlling power delivery to a first electrical device based at least in part on an input separate from the power signal delivered via the first and second electrical inputs.

41. The method of claim 40, wherein: The input includes user input.

42. The method of claim 40, wherein: The input includes environmental input from an environmental sensor.

43. The method of claim 40, wherein: The input is a processor input from a processor operable to compare a parameter related to the first electrical device to a threshold value.

44. The method of claim 32, further comprising receiving an input communication signal for controlling operation of the automatic transfer switch.

45. The method of claim 32, further comprising transmitting the outgoing communication signal to a remote processing platform.

46. ​​The method of claim 45, wherein The outgoing communication signal includes information regarding a status of one of: the automatic transfer switch and a connected piece of electrical equipment.

47. The method of claim 32, further comprising providing an indication when the monitored power reaches a predetermined state.

48. An automatic transfer switch comprising: a first electrical input for receiving power from a first power source; a second electrical input for receiving power from a second power source; an electrical output for outputting electrical power to one or more electrical devices; a power sensing and conversion module for monitoring power delivered by at least one of the first electrical input and the second electrical input and selectively coupling the electrical output to one of the first electrical input and the second electrical input based on the monitoring; a preferred source selector for selecting one of the first electrical input and the second electrical input as a preferred input to be connected to the electrical output under a default condition, wherein when a signal quality of the preferred input is acceptable, the preferred input is coupled to the electrical output, and when the signal quality of the preferred input is unacceptable, the other of the first electrical input and the second electrical input is a non-preferred input and coupled to the electrical output, the preferred source selector being operable to perform the selection of the preferred input by one of automatic selection based on a comparison of power signals provided by the first power source and the second power source and remote control, such that the selection of the preferred input can be performed without physically accessing the automatic transfer switch; and The communication module is configured to enable data communication between the automatic transfer switch and one or more data devices remote from the automatic transfer switch.

49. The automatic transfer switch of claim 48, wherein: The power sensing and conversion module is operable to switch between the first electrical input and the second electrical input based on a quality of a power signal delivered via one of the first electrical input and the second electrical input.

50. The automatic transfer switch of claim 48, wherein: The power sensing and conversion module is operable to monitor the power signals delivered via the first and second electrical inputs and connect one of the first and second electrical inputs to the electrical output based on the monitored power signals.

51. The automatic transfer switch of claim 48, wherein: The preferred source selector selects the preferred input based on user input.

52. The automatic transfer switch of claim 51, wherein: The preferred source selector selects the preferred input based on a comparison of power signals delivered via the first electrical input and the second electrical input.

53. The automatic transfer switch of claim 48, wherein: The power sensing and conversion module includes a first relay between the first electrical input and the electrical output, and a first solid-state switch between the first electrical input and the electrical output, each of the first relay and the first solid-state switch being operable to cycle the first electrical input and the electrical output to at least one of: connect and disconnect.

54. The automatic transfer switch of claim 53, wherein: The power sensing and conversion module includes a second relay between the second electrical input and the electrical output, and a second solid-state switch between the second electrical input and the electrical output, each of the second relay and the second solid-state switch being operable to cycle the second electrical input and the electrical output.

55. The automatic transfer switch of claim 53, wherein: The solid-state switch is operable to selectively cycle at or near a zero crossing of the power signal.

56. The automatic transfer switch of claim 48, further comprising a power control for controlling the delivery of power to the first electrical device based at least in part on an input separate from the power signal delivered via the first electrical input and the second electrical input.

57. The automatic transfer switch of claim 56, wherein: The input includes user input.

58. The automatic transfer switch of claim 56, wherein: The input includes environmental input from an environmental sensor.

59. The automatic transfer switch of claim 56, wherein: The input is a processor input from a processor operable to compare a parameter related to the first electrical device to a threshold value.

60. The automatic transfer switch of claim 48, wherein: The communication module includes a communication input for receiving an input communication signal for controlling the operation of the automatic transfer switch.

61. The automatic transfer switch of claim 48, wherein: The communication module includes a communication output for transmitting an output communication signal to a remote processing platform.

62. The automatic transfer switch of claim 61, wherein: The outgoing communication signal includes information regarding a status of one of: the automatic transfer switch and a connected piece of electrical equipment.

63. The automatic transfer switch of claim 48, further comprising a warning indicator for providing an indication when the monitored power reaches a predetermined state.

64. The automatic transfer switch of claim 48, wherein: The one or more data devices include a control module for one of: monitoring the automatic transfer switch and controlling the automatic transfer switch.

65. The automatic transfer switch of claim 48, wherein: The one or more data devices include a control module for one of: monitoring equipment connected to the automatic transfer switch and controlling equipment connected to the automatic transfer switch.

66. The automatic transfer switch of claim 48, wherein: The one or more data devices include an environmental sensor operable to provide an output via the data communications port.

67. The automatic transfer switch of claim 48, wherein: The one or more data devices include a control module and a connected piece of equipment.

68. The automatic transfer switch of claim 48, wherein: The automatic transfer switch is adapted to be attached to a rack structure of a rack having a plurality of spaces for mounting a plurality of pieces of electronic equipment, wherein the automatic transfer switch is attached to the rack structure and does not occupy any space of the rack.

69. The automatic transfer switch of claim 68, wherein: The automatic transfer switch includes a housing having a volume not exceeding 85 cubic inches.

70. The automatic transfer switch of claim 68, wherein: The automatic transfer switch includes a housing having a mounting slot for mounting to a DIN rail.

71. The automatic transfer switch of claim 48, wherein: The output is connected to a socket strip having a plurality of receptacles for receiving electrical plugs.

72. An automatic transfer switch comprising: shell; a first electrical input port extending through a wall of the housing for receiving power from a first power source; a second electrical input port extending through the wall of the housing for receiving power from a second power source; an electrical output port extending through a wall of the housing for outputting electrical power to one or more electrical devices; a preferred source selector for selecting one of the first electrical input and the second electrical input as a preferred input to be connected to the electrical output under a default condition, wherein when a signal quality of the preferred input is acceptable, the preferred input is coupled to the electrical output, and when the signal quality of the preferred input is unacceptable, the other of the first electrical input and the second electrical input is a non-preferred input and coupled to the electrical output, the preferred source selector being operable to perform the selection of the preferred input by one of automatic selection based on a comparison of power signals provided by the first power source and the second power source and remote control, such that the selection of the preferred input can be performed without physically accessing the automatic transfer switch; as well as a power sensing and conversion module for monitoring power delivered by at least one of the first electrical input and the second electrical input and selectively coupling the electrical output to one of the first electrical input and the second electrical input based on the monitoring; as well as Wherein, the housing is configured to be mounted to a DIN rail.

73. The automatic transfer switch of claim 72, wherein: The housing has a slot formed therein for receiving one of a DIN rail and a DIN rail mount.

74. The automatic transfer switch of claim 73, wherein: The slot is also configured to receive a head of a fastener for securing the housing to an equipment rack.

75. The automatic transfer switch of claim 74, wherein: The slot is configured to rotationally secure the head.

76. The automatic transfer switch of claim 75, wherein: The head is a slotted head, and the slot is configured to extend into the slot of the slotted head to rotationally secure the head.

77. The automatic transfer switch of claim 73, wherein: The housing includes vents for dissipating heat generated by the automatic transfer switch.

78. An automatic transfer switch comprising: a first electrical input for receiving power from a first power source; a second electrical input for receiving power from a second power source; an electrical output for outputting electrical power to one or more electrical devices; a preferred source selector for selecting one of the first electrical input and the second electrical input as a preferred input to be connected to the electrical output under a default condition, wherein when a signal quality of the preferred input is acceptable, the preferred input is coupled to the electrical output, and when the signal quality of the preferred input is unacceptable, the other of the first electrical input and the second electrical input is a non-preferred input and coupled to the electrical output, the preferred source selector being operable to perform the selection of the preferred input by one of automatic selection based on a comparison of power signals provided by the first power source and the second power source and remote control, such that the selection of the preferred input can be performed without physically accessing the automatic transfer switch; a power sensing and conversion module for monitoring power delivered by at least one of the first electrical input and the second electrical input and selectively coupling the electrical output to one of the first electrical input and the second electrical input based on the monitoring; as well as A current limiting device, associated with the power sensing and conversion module, is configured to limit a maximum current across the automatic transfer switch to within a defined operating range.

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