Power grid protection via transformer neutral interruption systems and triggered phase disconnection

Abstract

A protection circuit is disclosed. The protection circuit includes a direct current (DC) blocking component electrically connected between a transformer neutral and ground, and an overvoltage protection device electrically connected in parallel with the DC blocking component. The overvoltage protection device is constructed to repeatedly and reliably provide overvoltage protection in response to a voltage at the transformer neutral exceeding a threshold. The DC blocking component has an impedance below a predetermined value, thereby effectively grounding the transformer neutral. The DC blocking component remains continuously connected to the transformer neutral.

Description

[Technical Field]

[0001] This application was filed as a PCT international application on September 27, 2019, and claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 738,826, filed September 28, 2018, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates generally to electrical protection devices for electrical equipment, and more particularly, the present disclosure relates to systems for power grid protection, such as transformer neutral interruption circuits and voltage-triggered transformer phase disconnection. [Background technology]

[0003] Electrical systems, especially high-voltage, high-power electrical systems, can be damaged when a serious unexpected electrical event occurs. Specific examples of electrical systems and equipment that are vulnerable to damage include high-voltage transformers, generators, circuit breakers, and reactive power support equipment installed on the power grid.

[0004] Exposure to electromagnetic fields can cause various types of damage to electrical systems, especially those involved in sensitive circuits such as power grids. For example, electromagnetic pulse (EMP) and geomagnetic disturbance (GMD) events can cause interference or damage to electrical equipment, causing it to malfunction or become inoperable. Electrical equipment can also be destroyed by powerful EMP or geomagnetic storms. Detailed characteristics of EMP radiation are described in Non-Patent Document 1 and Non-Patent Document 2. In general, these types of electromagnetic fields can induce currents in power grids, which may include high-voltage transformers.

[0005] A further example of damage can occur in the case of geomagnetically induced currents (GICs). In such cases, significant induced currents can also occur in electrical equipment, but these currents have a more gradual appearance in the power grid (over seconds / minutes rather than within milliseconds). Detailed characteristics of geomagnetic storms are described in Non-Patent Document 3. HVDC systems operating near AC grid systems can induce ground currents that can affect the AC grid system through their earth connections. One example is in earth return mode, where the HVDC system can inject DC currents into the earth electrode, which can cause stray DC currents to flow in the neutrals of nearby transformers.

[0006] Each of the above example causes of damage can lead to the failure of power grid electrical components, such as high voltage transformers. This can cause undesirable consequences in the form of power outages for large populations / areas. Because these large transformers are expensive and generally difficult to relocate, any repairs or replacements of such transformers can take a significant amount of time to complete.

[0007] EMP E3 events contain components that occur relatively quickly (within milliseconds), while GIC-type events occur more slowly. Therefore, protection systems for power grid components are configured to protect against a subset of event types or are built to respond to various types of events, thus requiring fast and slow response times. These events are considered direct current (DC) or quasi-DC because they induce signals at lower frequencies compared to the 50 Hz or 60 Hz frequencies associated with power system signals.

[0008] An additional consideration is that equipment designed to protect power grid components from EMP E3 must be resistant and able to operate through the pre-EMP E1 and E2 components. This requires special shielding and design specifications. Mil-Std 188-125 describes these conditions and the necessary remediation, as does U.S. Patent No. 5,629,493. The shielding and protection required to make electronic equipment resistant to EMP E1 generally also protects it against other harmful high-frequency events, such as intentional electromagnetic interference (IEMI), as described in U.S. Patent No. 5,629,493.

[0009] One example protection system that can be used to protect against EMP / IEMI and GIC events is described in U.S. Patent No. 5,929,999. This patent describes a system in which the neutral connection is limited to a direct current (DC) interrupting component of the circuit between the transformer neutral and ground. During normal operation, a parallel circuit path directly connected to ground is maintained closed, and in the event of an EMP / IEMI or GIC event, a fast-acting switch opens.

[0010] While the systems described in the referenced patents are effective in protecting against such potentially harmful events, some power grid operators prefer to avoid the use of switching components due to the perception that switched-in components may be less reliable than those permanently included in the protection circuit. As such, such system operators may choose to employ other solutions that do not require the use of switches to selectively introduce circuit components into the protection circuit.

[0011] Protection circuits and related systems that do not require active detection of damaging events and switching to react to such events are considered "passive systems" in this disclosure. These passive systems may incorporate automatic bypass switches that bypass DC blocking components under various conditions ("passive systems with automatic bypass") or may be constructed without automatic bypass switches ("fully passive systems"). These may be contrasted with "active systems" that automatically and selectively introduce DC blocking components into the circuit between the transformer neutral and ground.

[0012] A variety of passive systems exist. A common component is an overvoltage protection device (e.g., using a spark gap or metal oxide varistor (MOV)) that may be included between the transformer neutral and ground. However, in most systems, existing overvoltage protection devices are not constructed to withstand multiple fault events. The extremely high currents associated with faults on the bulk power system require the overvoltage protection system to be bypassed and reset or repaired before the system can be returned to service. Spark gaps typically erode significantly under the stress of a fault event, and this erosion of material significantly changes the breakdown voltage at which the gap will ignite, reducing or eliminating their effectiveness as overvoltage protection devices by increasing the breakdown voltage to unacceptably high levels. In the case of solid-state devices such as MOVs or thyristors, the high currents heat the device, requiring extended cooling periods before it can be used again. This is one reason why automatic bypass switches have been required in passive systems.

[0013] Furthermore, existing passive protection circuits have drawbacks regarding their operation in the absence of a damaging event. For example, linear resistors included "full-time" in such passive systems (i.e., not switched in / out by bypass switching, etc.) leave a significant resistance in the connection between the transformer neutral and earth during normal operation. This can have problematic effects, such as limited effectiveness unless relatively high value resistors are used, adversely affecting transformer insulation levels and earth fault relaying schemes, and leaving the system without an effectively earthed neutral. Also, the neutral resistor may require forced cooling if the neutral current (due to system unbalance) is not zero. 2 Transformers may also have R losses. Furthermore, linear resistance does not prevent harmonics due to GIC. Transformers can still saturate during a GMD or EMP event, inducing harmonics that can be transmitted to the distribution network, causing business loss, customer equipment damage, and, in severe cases, voltage collapse.

[0014] Therefore, no existing device meets all of the requirements of power grid operators in terms of both perceived reliability and actual responsiveness to potentially harmful voltage / current events within the power grid. Furthermore, existing passive devices only provide protection until the device reaches its DC withstand voltage limit, at which point it is no longer able to protect the transformer. This is problematic for scenarios where very large DC currents are expected, such as a large GMD or EMP event. In such an event, induced currents and voltages within the power grid can result in damage to transformers and associated circuits, not only at the monitored location but also elsewhere in the power grid.

[0015] For these and other reasons, improvements are desirable. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] U.S. Patent No. 8,878,396 [Non-patent literature]

[0017] [Non-Patent Document 1] “High Altitude Electromagnetic Pulse Protection for Ground Based C4I Facilities Performing Critical, Time-Urgent Missions”, Military Standard 188-125 [Non-patent document 2] “The Late-Time (E3) High-Altitude Electromagnetic Pulse (HEMP) and Its Impact on the US Power Grid”, Oak Ridge National Laboratories Meta-R-321 [Non-patent document 3] “Geomagnetic Storms and Their Impacts on the US Power Grid”, Oak Ridge National Laboratories Meta-R-319 [Non-patent document 4] “Electromagnetic Environmental Effects Requirements For Systems”, Military Standard 464 [Non-Patent Document 5] "High-power electromagnetic (HPEM) environments - Radiated and conducted", IEC 61000-2-13 Summary of the Invention [Means for solving the problem]

[0018] In accordance with the following disclosure, the above and other problems are addressed by:

[0019] In a first aspect, a protection circuit is disclosed. The protection circuit includes a direct current (DC) blocking component electrically connected between a transformer neutral and ground, and an overvoltage protection device electrically connected in parallel with the DC blocking component. The overvoltage protection device is constructed to repeatedly and reliably provide overvoltage protection in response to a voltage at the transformer neutral exceeding a threshold. The DC blocking component has an impedance below a predetermined value, thereby effectively grounding the transformer neutral. The DC blocking component remains continuously connected to the transformer neutral.

[0020] In a second aspect, an electrical protection system includes a transformer assembly having one or more connections, each connection associated with a different power line phase of an AC power signal or all three phases of the AC power signal. The system further includes a voltage measurement device that transmits a signal upon detecting a voltage across the transformer neutral and ground, and at least one breaker electrically connected to the power line phase of the transformer. The system further includes a DC neutral interruption circuit electrically connected between the transformer neutral and ground. The system includes a processor that receives a signal from the voltage measurement device, the processor being electrically connected directly or indirectly to the at least one breaker and configured to, upon receiving a signal from the voltage measurement device, transmit a signal to open the at least one breaker electrically connected to the power line phase of the transformer in response to the processor determining that the voltage across the transformer neutral and ground is above a predetermined threshold.

[0021] In some embodiments, exceeding a predetermined threshold will result in overvoltage protection devices catching fire or there is a risk of exceeding the DC voltage withstand limits of DC interrupting components and / or the transformer neutral insulation. The objective is to interrupt as much DC current as possible and then safely open the large phase circuit breaker, de-energizing the transformer and removing it from damage only when absolutely necessary, before the DC voltage withstand limits are reached or DC current inrush begins.

[0022] In a further aspect, a method of protecting a power grid against damage due to induced currents or voltages at the neutral points of power grid transformers within the power grid is disclosed. The method includes detecting a voltage at a transformer neutral point of a first transformer within the power grid having a characteristic indicative of potential damage to electrical equipment contained within the power grid, and selecting one or more transformers within the power grid other than the first transformer, the one or more transformers associated with phase breakers and control circuits. The method further includes sending an activation command to control circuits associated with the one or more transformers indicating to the control circuits to open the phase breakers, thereby segmenting the power grid and essentially "shorting the line," which would result in a voltage sag at the first transformer. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a perspective view of an example embodiment of a passive transformer neutral blocking circuit according to one possible embodiment of the present disclosure, as installed at a power generation or distribution substation site. [Figure 2] FIG. 10 is a perspective view of a passive transformer neutral interruption circuit according to a second possible embodiment of the present disclosure. [Figure 3A] FIG. 10 is a perspective view of a passive transformer neutral blocking circuit according to a further possible embodiment of the present disclosure. [Figure 3B] FIG. 10 is a perspective view of a passive transformer neutral blocking circuit according to a further possible embodiment of the present disclosure. [Figure 4] FIG. 10 is a perspective view of a passive transformer neutral blocking circuit coupled with sensing and control electronics according to a further possible embodiment of the present disclosure. [Figure 5] FIG. 10 is a perspective view of a passive transformer neutral interruption circuit with a maintenance and AC breaker switch according to a further possible embodiment of the present disclosure. [Figure 6] FIG. 10 is a perspective view of a passive transformer neutral blocking circuit according to a further possible embodiment of the present disclosure. [Figure 7] FIG. 10 is a perspective view of a passive transformer neutral interruption circuit signaling a phase circuit breaker according to a further possible embodiment of the present disclosure. [Figure 8A] FIG. 8 illustrates an example overvoltage protection device that can be used in the passive transformer neutral point interruption circuits of FIGS. 1-7. [Figure 8B] FIG. 8 illustrates an example overvoltage protection device that can be used in the passive transformer neutral point interruption circuits of FIGS. 1-7. [Figure 8C] FIG. 8 illustrates an example overvoltage protection device that can be used in the passive transformer neutral point interruption circuits of FIGS. 1-7. [Figure 8D] FIG. 8 illustrates an example overvoltage protection device that can be used in the passive transformer neutral point interruption circuits of FIGS. 1-7. [Figure 9] FIG. 1 is a front view of an example embodiment of a passive overvoltage protector assembly. [Figure 10] 1 is a plot of the DC voltage on the transformer neutral when high DC or quasi-DC current is interrupted. DETAILED DESCRIPTION OF THE INVENTION

[0024] Various embodiments of the present invention will now be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the claims appended hereto. Additionally, any examples set forth herein are not intended to be limiting, but merely set forth some of the many possible embodiments for the claimed invention.

[0025] Generally, this disclosure describes systems and methods for protecting electric utility transformers and other electrical or electromechanical equipment from harmful DC currents and resulting harmonic content on power lines. Large DC neutral currents and harmonics can be the result of geomagnetic (solar) storms, high altitude electromagnetic E3 pulses (HEMP-E3), or HVDC operating in ground return mode.

[0026] Overall, this disclosure describes methods and systems for passively interrupting or reducing potentially harmful neutral DC currents and preventing the generation of harmonic components of 50 Hz or 60 Hz power line sources to protect critical electrical equipment. The described methods and systems require little maintenance, and the DC interruption circuitry does not require the use of active components such as switches, allowing for continuously maintained protection. Additionally, the described systems and methods employ low-impedance capacitors or capacitor banks to provide an effectively grounded transformer, thereby avoiding potential problems in power systems associated with threshold settings for relay protection systems. An electrical circuit is effectively grounded when it meets the definition for grounding set forth in IEEE Standard C62.91.

[0027] In accordance with this disclosure, a protective circuit referred to herein as having a "persistently maintained" DC interrupting function means that such DC interrupter remains connected to the transformer neutral and is not bypassed, at least during operation. For purposes of illustration, a device having a manual bypass switch for maintenance purposes (i.e., for manual disconnection during periods of non-operation when service is required) would be persistently maintained, while a device having an automatic or electronically controlled switch that allows switching between operating modes during transformer operation would not persistently maintain a DC interrupting component at the transformer neutral. Furthermore, a device having an automatic switch that is used only during maintenance operations but is configured not to operate to bypass the DC interrupting component in response to operating conditions would also be a circuit that persistently maintains a DC interrupting function during operation of the circuit.

[0028] The passive transformer neutral interruption system disclosed herein provides a grounding scheme that is compatible with standard transformer grounding schemes and therefore will not require modifications to power system relay settings in typical situations. When high DC (or quasi-DC) currents or voltages or high harmonic power components are present, DC interruption components interrupt or dampen DC or quasi-DC currents in the system. Interrupting quasi-DC or DC currents prevents half-cycle saturation of transformers, thereby protecting them from excessive reactive power losses, overheating, and damage. Additionally, interrupting DC currents prevents the generation of harmonics in partially saturated transformers. Such power harmonics can trip power system relays, which can in turn cause localized or widespread power outages. Whenever an overvoltage event occurs, or consecutive overvoltage events occur within a short period of time, a passive overvoltage protection device (OVPD) can operate to protect components from overvoltages. The overvoltage protection device, according to various example embodiments of the present disclosure, may include one or more of the following: a spark gap, a metal oxide varistor, a silicon carbon varistor, a variable resistor, a surge arrester, or any other suitable component designed to form a path to ground away from the protected component for signals that exceed a threshold voltage.

[0029] In example embodiments, the disclosed systems and methods enable interruption of geomagnetically induced currents (GICs) and prevent the generation of harmonic signals while maintaining a low-impedance, low-resistance connection to ground to maintain an effective alternating current (AC) ground connection for power line transformers. Therefore, relay resetting is not required. Additionally, overvoltage protection devices can be included that handle repeated high-current and high-voltage faults without a cool-down period or the need for a bypass switch. Additionally, because the circuit is passive, it is not necessary to include EMP shielding or filtering functionality that would be required on an automatic bypass switch, and no triggering is required in the event of the detection of potentially harmful DC, harmonic, or EMP-El pulses, thereby simplifying the overall circuit.

[0030] Furthermore, in example embodiments, if the DC voltage at the transformer neutral reaches a threshold that approaches the withstand limit of the DC blocking components or the insulation of the transformer neutral, the system of the present disclosure signals a large AC phase breaker to open, safely shutting off the transformer and protecting it from the inrush of high DC current, rather than flipping an automatic switch that bypasses the DC blocking components or triggers an overvoltage device (which would allow DC current to flow).

[0031] FIG. 1 illustrates a generalized embodiment of a passive transformer neutral interruption system 100 according to the present disclosure. The passive transformer neutral interruption system 100 is generally connected between a transformer neutral 10 of a transformer 12 and ground 14. The passive transformer neutral interruption system 100 includes a DC interruption component 110 connected between a connection to the transformer neutral 10 and ground 14. As further described in the examples below, the DC interruption component 110 may include one or more direct current interruption devices (e.g., capacitors or resistors) between ground 14 and the transformer neutral 10 to prevent harmful DC or quasi-DC ground currents at the transformer neutral 10, which could in turn cause damage to the transformer 12. Depending on the particular application, capacitive or resistive (or some combination thereof) interruption devices 110 may also be used. Various configurations of DC interruption components are described, for example, in U.S. Pat. No. 8,878,396, the disclosure of which is incorporated herein by reference in its entirety. By comparison, however, in that patent the DC blocking component is selectively removable from the circuit between the transformer neutral 10 and ground via a switching arrangement operable to bypass the DC blocking component as part of the system's protection scheme. In the present application, a passive overvoltage device may instead be used to discharge high DC voltage events that would otherwise have the potential to damage the system 100.

[0032] According to the present disclosure, a passive overvoltage protection device (OVPD) 112 can be connected in parallel with the DC blocking component 110 between the transformer neutral 10 and ground 14 to protect the DC blocking component and the transformer. The passive OVPD 112 can maintain protection in the event of multiple overvoltage events within a short period of time. The passive OVPD 112 can include any number of devices, as described above and further described in the examples below. The overvoltage protection device, according to various example embodiments of the present disclosure, can include one or more of the following: a spark gap, a metal oxide varistor, a silicon carbon varistor, a variable resistor, a surge arrester, or any other suitable component designed to create a path to ground away from the protected component for signals exceeding a threshold voltage. In example embodiments, the passive OVPD 112 can also include, for example, a specific type of spark gap constructed to nondestructively discharge repeated overvoltage events. An example spark gap that can be used as the OVPD 112 is described in U.S. Patent No. 9,660,441, entitled "Overvoltage Protection For Power Systems," the disclosure of which is incorporated herein by reference in its entirety. Alternative versions of such devices are described below in connection with Figures 8A-8D and 9.

[0033] The passive OVPD 112 provides protection for the passive transformer neutral interruption system 100 and the transformer 12 and is useful in the event of a fault or large DC or quasi-DC voltage that exceeds the capability of the DC interrupting or limiting devices, such as those that may be caused by a large GMD or HEMP-E3 event. In the event of a large GMD or HEMP-E3 event, some utilities may prefer to interrupt DC up to the DC voltage withstand limit of the DC interrupting device and then trigger open the large AC phase breaker, thereby de-energizing the transformer before the passive OVPD is triggered and DC current begins to flow.

[0034] 2, a further embodiment of a passive transformer neutral interruption system 200 is shown. In this embodiment, the passive transformer neutral interruption system 200 includes a power resistor 204. The power resistor 204 adds sufficient resistance to damp any ferroresonance and reduces the voltage across the capacitor bank during a fault or transient event, limiting the discharge current from the capacitor bank. In an example embodiment, the power resistor 204 may have a value typically between 0.3 and 5.0 ohms.

[0035] Referring now to FIG. 3A, a further embodiment of a passive transformer neutral interruption system 300 is shown. In this embodiment, the DC interruption component consists of a bank of electrically parallel-connected capacitors 310a-n, commonly referred to as capacitor bank 310. Capacitor bank 310 lowers the system impedance by adding additional capacitance. FIG. 3B shows a further embodiment with capacitor banks 320a-n, which increase the system voltage standoff by adding capacitors in series. When high-impedance capacitors are used, relays may be required to reset, so the use of such low-impedance capacitor banks may be preferred. A low-impedance capacitor bank is also important for maintaining an effective ground according to the definition of IEEE Standard C62.91 for grounding. Power system relays (e.g., relays connected to power line phases) are networked and work together to clear ground faults based on the signal level transmitted on the power line phases.

[0036] 4, a further example embodiment of a passive transformer neutral interruption system 400 is shown. In this example embodiment, a neutral current monitor 402 is connected between the DC interruption component 110 and ground 14 and between the passive OVPD 112 and ground. The neutral current monitor 402 measures AC current on the power system and, together with an electronic module 408, can be used to determine when maintenance on the power system is required. In some embodiments, the neutral current monitor 402 can be a Rogowski coil or a current transformer.

[0037] 4 also illustrates an electronics module 408 according to one possible embodiment of the present disclosure. The electronics module 408 can monitor the overall performance of the neutral circuit breaker and the transformer and report the results via a communications network 412 to a control room 414. The control room 414 can be local or remote from the electronics module 408. FIG. 4 includes a voltage measurement device 406, in this example, for reporting the voltage between the transformer neutral 10 and ground to the electronics module 408.

[0038] In the illustrated embodiment, the electronics module 408 is enclosed within a shielded enclosure 410 to prevent high frequency, high power electromagnetic signals from entering the enclosure and thereby exposing sensitive electronic equipment to potential interference and damage. The electronics module may include control circuitry, implemented as, for example, a microprocessor and / or communications circuitry, as well as signal conditioning circuitry usable to receive inputs from the neutral point monitoring device 402 and / or voltage measurement device 406, for example, to generate notifications of various events observed within the transformer neutral 10 and system 400, or throughout much of the entire power grid.

[0039] In the illustrated embodiment, the shielded enclosure 410 is an EMP / EMI Faraday shielded enclosure with conductive seals around all door openings to provide radiation protection from electromagnetic frequencies typically between about 14 kHz and 10 GHz.

[0040] Referring now to FIG. 5 , a further embodiment of a passive transformer neutral interruption system 500 is shown. In this example, both a maintenance bypass switch 502 and an AC circuit breaker 504 are shown. According to various embodiments of the present disclosure, the maintenance bypass switch 502 enables safe maintenance of the passive transformer neutral interruption circuit, and the AC circuit breaker 504 enables safe operation of the maintenance bypass switch 502 by preventing arcing across the maintenance switch 502. The maintenance switch 502 is normally closed and connected between the transformer neutral 10 and the passive transformer neutral interruption circuit, while the AC circuit breaker 504 is normally open and connected between the transformer neutral 10 and ground 14. The neutral current monitor 402 can also be used to measure neutral AC imbalance and determine when it is safe to operate the maintenance switch 502. As described above, the maintenance switch 502 remains closed unless manually opened, thereby maintaining the DC interruption component 110 continuously within the system 500.

[0041] Referring now to FIG. 6 , a further embodiment of a passive transformer neutral interruption system 600 is shown. In this embodiment, the electronics module 408 includes multiple filters 622 disposed around the periphery of the enclosure 410. The filters 622 may typically be low-pass or band-pass filters with surge suppression to suppress signals that could adversely affect the performance of the electronics and signal processing components inside the enclosure. In such an embodiment, filtering is present on all conductive wires passing through the enclosure 410 to ensure protection. Additionally, in the illustrated embodiment, filters 622 are disposed on the power input 634 as well as on the output to the system operator. Additional filters 622 are electrically connected between the sensing electronics 624 and one or more electromagnetic detectors 650. The electromagnetic detectors 650 may be, for example, shielded magnetic loop antenna-based detectors configured to detect EMP / IEMI events. An example of such a detector is described in U.S. Pat. No. 8,773,107, the disclosure of which is incorporated herein by reference in its entirety.

[0042] 6, sensing electronics 624 can be used to detect signals from neutral point monitoring device 402 and / or voltage measurement device 406 and report these signals, for example, to a control room located either locally or remotely from electronics 624. Sensing electronics 624 can include programmable circuitry, such as a microprocessor or programmable gate array type device, as well as memory usable to store instructions for defining signal thresholds (current and / or voltage) at which messages can be generated. Sensing electronics 624 can also be configured to generate actuation signals to take specific actions in response to observed current and / or voltage events, as described below.

[0043] 7, there is shown a further embodiment of a transformer neutral interruption system 700. In this embodiment, a high voltage breaker 702 is electrically connected to the power line phases of the transformer 12. An example of such a neutral interruption system is described in U.S. Patent Application No. 15 / 887,781, the disclosure of which is incorporated herein by reference in its entirety.

[0044] During operation of the transformer neutral interruption system 700, the voltage measurement device 406 can report the DC voltage across the transformer neutral 10 to ground 14 to the electronics module 408, which can determine that the DC voltage indicates an event that could be damaging to the DC interruption component 110 (e.g., exceeding the rated voltage of a particular capacitor or capacitor bank) or the transformer itself (e.g., at a level where damage to insulating materials within the transformer is possible). Still other types of damage within the overall system 700 can also be detected by the electronics module 408, and may be based, for example, on instantaneous DC voltages exceeding a predetermined threshold or a rate of change of DC voltages exceeding a predetermined threshold rate (as described above). The electronics module 408 can then send a signal to open one or more of the high-voltage breakers 702 to prevent triggering of the passive OVPD 112 for DC voltages above a DC threshold, as further described below with reference to FIG. 10 . 7 can be set below the DC voltage that triggers the passive OVPD 112, thereby preventing the DC current that can flow when the passive OVPD 112 is triggered. Additionally, the high voltage breaker 702 can be controlled by the control room 414, for example, via communication with the electronics 408 over the communication network 412.

[0045] In some embodiments, the system may also include an electromagnetic detector, such as electromagnetic detector 650 shown in Figure 6. In such a configuration, the system is configured to respond to an EMP / EMI event, so that the high voltage breaker can be shielded to ensure proper operation and protection during such an event.

[0046] With general reference to FIG. 7 , it is noted that the transformer neutral interruption system described herein can have many advantages in operation. Specifically, activation of the high voltage breaker 702 in the event of a potentially harmful DC current means that the transformer remains protected, while the high voltage breaker 702 can be activated by an activation signal from the electronics module 408. As noted above, such an event can include, for example, detection by the electronics module 408 that the voltage measurement device 406 (e.g., a voltage probe or other voltage measurement device) has sensed a voltage above a predetermined threshold or above a predetermined threshold for a predetermined period of time. Furthermore, the electronics module 408 can trigger the high voltage breaker 702 with an activation signal in response to a voltage change that exceeds an acceptable rate of change, for example, due to a fast voltage rise time. In an example embodiment, a voltage change rate of about 100 V / ms to about 175 V / ms can exhibit a fast rise time that is distinguishable from normal AC current.

[0047] Additionally, activation of the high-voltage breaker can have further benefits. For example, activation of the circuit breaker 702 can result in the transformer 12 being disconnected from the entire power grid, or at least segmenting the power grid. If an induced DC voltage on the transformer neutral or power line phases (the magnitude of which is determined on a volts-per-meter basis) can occur, the length over which the voltage can be induced is shortened, potentially resulting in a shorter segment in the power grid, resulting in a lower DC voltage. This segmentation therefore also protects against potential damage to the transformer 12 or the DC interrupting component 110.

[0048] In example embodiments in which electronics 408 communicates with control room 414 (or other electronics 408 located in association with other transformer neutral protection circuits associated with other power grid transformers), either electronics 408 or control room 414 can transmit signals directed to electronics associated with different transformers via communication network 412. In this manner, detection of a high DC voltage event (or rate-of-change voltage event) occurring in one transformer can trigger immediate segmentation of the power grid in a manner that would prevent damage elsewhere in the power grid, without relying on each protection circuit having to sense such an event. Furthermore, in example embodiments, electronics 408 or control room 414 can execute an algorithm to select which protection systems, among multiple protection systems in the power grid, will receive such an activation command and open high-voltage breakers on phases of other power grid transformers. This can include, for example, identifying transformers that can safely segment the power grid into segments having lengths that are unlikely to induce significant high voltages while maintaining connectivity to as many sources of power as possible on the power grid. This segmentation may be based on the distance between the transformers (and thus the length of the segments created) or the distance between the generating station and the transformer to be disconnected (e.g., to minimize the population experiencing power loss due to breaker tripping). In some cases, an algorithm is applied that combines these factors with the voltages occurring to select the specific transformer protection circuit to which a breaker tripping signal should be sent.

[0049] 7, it is noted that activation of high voltage breaker 702 may be advantageous in combination with the passive neutral interruption devices of the present disclosure, as well as other types of passive and active neutral interruption devices described in the patents and publications incorporated by reference herein. For example, activation of high voltage breaker 702 may be performed in response to detection of a specific DC voltage while maintaining a DC blocking component in the system, as described with respect to the passive mode system described herein. However, that activation may be performed in combination (or independently, but within the same circuit) with the activation of a switch that selectively bypasses or selectively introduces a DC blocking component between the transformer neutral and ground, as shown in U.S. Pat. No. 8,878,396.

[0050] 10, a plot 1000 of DC voltage observed at the transformer neutral as a function of time is shown, with various thresholds indicated for purposes of explaining the operation of the system described herein. It is noted that in this figure, and in conjunction with the overall disclosure, the terms DC voltage or DC current refer to both DC and quasi-DC voltages or DC and quasi-DC currents, respectively.

[0051] In plot 1000, the DC voltage occurring at the transformer neutral (e.g., as detected by voltage measurement device 406) is shown. In the illustrated example, DC neutral interrupt component 110 may have a DC voltage withstand limit corresponding to DC voltage level C, such that DC voltages above this limit may begin to destroy or damage DC neutral interrupt component 110, put the transformer at risk of damage, and / or damage the insulation within transformer 12 itself. These thresholds are commonly referred to as the withstand voltage or withstand voltage limit of the DC neutral interrupt component and / or the transformer insulation, respectively. Example ranges of voltages are provided below:

[0052] Additionally, passive OVPD 112 can be set to trigger at a voltage level B, which is lower than DC voltage level C, to protect both DC neutral interrupt component 110 and transformer 12 from damage in the event of an overvoltage event (e.g., a fault). DC voltage limit B can typically be slightly lower than the rated voltage of DC neutral interrupt component 110 or transformer 12 and can be within the ranges noted below.

[0053] It is noted that triggering the passive OVPD 112 at voltage level B would result in undesired DC current flowing to ground. Therefore, when using the various circuit variations described above in connection with FIG. 7, the electronics module 408 can be configured to send an actuation signal to open one or more of the high voltage breakers 702 at DC voltage level A. DC voltage level A is typically set lower than voltage level B to prevent the passive OVPD 112 from triggering on a DC voltage, thereby safely de-energizing the transformer before high DC current inrush can occur.

[0054] In some embodiments, the transformer 12 may have a DC voltage limit of 35 kV, above which the risk of transformer neutral insulation degradation is deemed unacceptable. In some embodiments, the DC withstand voltage limit of the DC blocking component 110 is in the range of 16-34 kV DC, corresponding to DC voltage level C. Accordingly, the passive OVPD 112 may have a DC trigger voltage configured to be in the range of approximately 8-15 kV DC, corresponding to voltage level B. The electronic module 408 may be configured to open one or more high-voltage breakers 702 at a DC voltage level in the range of approximately 7-14 kV DC, corresponding to DC voltage level A. In still other embodiments, the voltage limit of the transformer 12, the withstand limit of the DC blocking component 110, the trigger voltage of the passive OVPD 112, and the voltage level at which the electronic module opens the one or more high-voltage breakers may differ from those described above, although the relative order of operation will generally be selected to protect against damage to the DC neutral interrupting component 110 or the transformer 12.

[0055] 8A-8D, an example of a passive OVPD that can be used in conjunction with the passive protection circuits described above is provided. FIG. 8A is a perspective view of a passive OVPD assembly 800 according to an example embodiment. Passive OVPD assembly 800 includes multiple subassemblies 801 a-c and circuit leads 802 a-b (802 b is shown in FIG. 8B). The subassemblies are connected in parallel to circuit leads 802 a-b. In addition, each of subassemblies 801 a-c includes a spark gap 806 a-c. While three subassemblies are shown in this figure, other embodiments include more or fewer subassemblies. Subassemblies 801 a-c include conductors 803 a-c (e.g., generally formed as a Jacob's ladder) and spark gaps 806 a-c in narrow regions of electrodes 810 a-c.

[0056] In some embodiments, the widths of the spark gaps 806a-c are substantially the same. When a large ground fault current triggers the breakdown voltage of one of the spark gaps 806a-c, a portion of the corresponding electrode surrounding that spark gap may ablate, causing a change in the width of the spark gap. This change in spark gap width may be an increase, which will cause a corresponding increase in the breakdown voltage of that particular spark gap. In some cases, the breakdown voltage of the spark gap after ablation caused by the large ground fault current will be greater than the breakdown voltage of one of the other spark gaps. Therefore, during the next large ground fault current, an arc will initiate at a different spark gap. In this way, the assembly 800 will have a longer life and will withstand multiple large ground fault currents.

[0057] In a further embodiment, and in addition to the above feature of a maintained breakdown voltage by the parallel arrangement, the spark gap width of one of the spark gaps 806a-c can be constructed in such a way that it is substantially ablatively resilient so that it is maintained overall after a large ground fault current is triggered, with the Lorentz force pushing the breakdown arc out of the spark gap region toward the end of the electrode, thus preserving the spark gap area. In such a configuration, the breakdown voltage may not result in a substantial change in gap width and a resulting increase in the breakdown voltage of that particular spark gap over multiple strikes. Generally, the spark gap breakdown voltage is required to remain within some predetermined range over a specified number of events.

[0058] In some embodiments, the passive OVPD assembly 800 may be subjected to an overvoltage event corresponding to a breakdown voltage above 5-8 kV and below 28 kV, with a current above 8,000 amperes for at least 60 milliseconds. In another example, the overvoltage event may correspond to a breakdown voltage above 5-8 kV and below about 35 kV, with a current above about 5,000 amperes for at least 40 milliseconds. Still other thresholds may be established, with example thresholds described in U.S. Patent No. 9,660,441, previously incorporated by reference.

[0059] FIG. 8B is a front view of subassembly 801a of passive OVPD assembly 800. Subassembly 801a includes mounts 804a-b, which support conductors 803a-c, of which only conductor 803a is shown for perspective. Each of conductors 803a-c is formed from a lower conductor and an upper conductor, shown as lower conductors 805a-b and upper conductors 807a-b, respectively. Additionally, electrodes 810a-b are formed at the junctions of the lower and upper conductors. The support structure for passive OVPD assembly 800 includes insulators 814a-b and cylindrical shields 816a-b, in combination with mounts 804a-b.

[0060] The mounts 804a-b are rigid support structures configured to secure and support the conductors 805a-b at a desired angle, as shown. In some embodiments, the mounts are configured to position the conductors 805a-b at an angle of 2.5 to 20 degrees from vertical. In an alternative embodiment, the angle of the conductors can be varied, for example, an angle between approximately 2 and 90 degrees can be used. Generally, this angle facilitates any discharge arc current forming across the electrodes 810a-b toward the upper conductors 807a-b, at least in part due to the large Lorentz forces that occur with arc currents in the voltage and current ranges outlined above. The mounts 804a-b are configured to withstand the Lorentz forces generated between the conductors 805a-b when an arc current forms.

[0061] Generally, bottom conductors 805a-b (also referred to herein as circuit leads) and top conductors 807a-b (also referred to herein as extensions) are large diameter cylindrical rods that join to form conductors 803a-c, with electrodes 810a-b formed at the junctions of the bottom and top conductors. The diameters of conductors 805a-b and 807a-b are selected based on the expected arcing current for a given application of overvoltage protection assembly 800. Conductors 805a-b are angled toward each other so that electrodes 810a-b are adjacent to each other. In some embodiments, the angle of inclination between conductors 805a-b is between 5 and 40 degrees. Electrodes 810a-b are separated by spark gap 806a.

[0062] In some embodiments, bottom conductors 805a-b, top conductors 807a-b, and electrodes 810a-b are integrally formed from a high-melting-point, rigid, conductive material. For example, in some embodiments, conductors 805a-b, 807a-b, and electrodes 810a-b are formed from a copper / tungsten alloy. In other embodiments, conductors 805a-b, 807a-b, and electrodes 810a-b are formed from different materials, such as tungsten, copper, and niobium.

[0063] Additionally, the spacing between electrodes 810a-b is further fixed by insulators 814a-b. Insulators 814a-b are rigid and formed from an insulating material. In some embodiments, insulators 814a-b have a cylindrical shape. Insulators 814a-b are configured to fix the spacing between mounts 804a-b, conductors 805a-b, and electrodes 810a-b, and therefore the width of spark gap 806. In example embodiments, one or more of insulators 814a-b are oriented in the direction of arc current formation across electrodes 810a-b, thereby providing additional reinforcement in that direction to avoid damage to passive OVPD assembly 800 in the event of arc current formation due to Lorentz forces in the direction of the arc current.

[0064] In some embodiments, shields 816a-b are included. In the illustrated example, the shields are metal tabs disposed between the insulators 814a-b and the supports 804a-b and configured to prevent the formation of conductive paths (from deposited carbon or material ejected during the arc) along the surfaces of the insulators 814a-b. In alternative embodiments, the shields 816a-b can be different shapes, e.g., cylindrical, surrounding the insulators 814a-b.

[0065] FIG. 8C is an enlarged front view of passive OVPD assembly 800. Subassembly 801a includes conductors 805a-b and 807a-b and electrodes 810a-b, with spark gap 806a separated by a distance smaller than the bottoms of electrodes 810a-b. For example, in some embodiments, the tops of electrodes 810a-b are separated by a first width W1, and the bottoms of electrodes 810a-b are separated by a slightly larger second width W2. In some embodiments, width W1 is 0.65 millimeters and width W2 is 0.82 millimeters. In other embodiments, width W1 is between 0.5 millimeters and 1 millimeter, and width W2 is between 0.75 millimeters and 1.25 millimeters. In yet other embodiments, width W1 is between 0.25 millimeters and 10 millimeters, and width W2 is between 0.4 millimeters and 20 millimeters. In some embodiments, the difference between the first width and the second width is approximately 0.4 millimeters. In other embodiments, the difference between the first width and the second width is between 0.15 and 15 millimeters. In some embodiments, the flat surfaces of electrodes 810a-b have a height H. In some embodiments, height H is 1 inch. In other embodiments, height H is between 0.5 and 4 inches. However, other embodiments with other heights and other first and second widths are possible as well. In some embodiments, height H is between 5 and 15 millimeters. However, other embodiments with other heights and other first and second widths are possible as well. For example, widths W1 and W2 can be the same, resulting in a spark gap with parallel surfaces. This is not optimal because it provides less control over where the spark will occur, but it is operable. During the initial high ground fault voltage, arc current forms at the top of electrodes 810a-b. As material is ablated during a high ground fault current event, the arc initiates at a lower point in the spark gap 806.Nevertheless, ablation at the spark gap is minimized by the passive OVPD assembly 800, particularly the shape of the conductors 803a-b, which ensures that ablation occurs at the ends of the conductors 807a-b (at the ends of the extensions).

[0066] It is noted that assembly 800 is constructed to withstand breakdown voltages below 35 kV (but typically above about 5-8 kV) and currents in excess of 5,000 amperes for at least 40 milliseconds, however, in alternative embodiments, assembly 800 can be constructed to withstand greater or lower breakdown voltages and / or currents, or to withstand such power losses for other periods of time.

[0067] Additionally, it is noted that the specific distance between electrodes 810a-b can be adjusted by adjusting the position of each of conductors 803a-b within mounts 804a-b, respectively. For example, due to the angle of bottom conductors 805a-b, mounting conductors 803a-b and extending them further from the mount can cause electrodes 810a-b to have less distance between them, while mounting conductors 803a-b and extending them a shorter distance from the mount will cause the electrodes to be spaced further apart. Thus, the precise breakdown voltage can be selected based on the distance between the electrodes.

[0068] FIG. 9 is a front view of one particular example embodiment of a passive OVPD assembly 900. Subassembly 901a includes conductor 905a with cross-sectional area 915a, conductor 907a with cross-sectional area 917a, spark gap 906, and cross-sectional area 918a formed by junction 908a of conductors 905a and 907a in the region of spark gap 906. Specifically, in some embodiments (e.g., as part of electrodes 810a-b described above), a flat surface can be formed in the region of the spark gap, and can be particularly flattened in the trapezoidal electrode region shown in FIG. 8C above. In some embodiments, conductors 905a and 907b can be generally cylindrical with circular or elliptical cross-sectional areas 915a and 917a. In other embodiments, conductors 905a and 907a can have other geometries with other cross-sectional geometries. In some embodiments, conductor 905b has substantially the same shape and cross-sectional area as 905a, conductor 907b has substantially the same shape and cross-sectional area as 907a, and junction 908b has substantially the same shape and cross-sectional area 918b as junction 908a and cross-sectional area 918a.

[0069] FIG. 9 also shows lengths A and B of cross-sectional area 917a, lengths C, D, and G of cross-sectional area 918a, and lengths E and F of cross-sectional area 915a. In some embodiments, lengths A, B, E, and F are all 1 inch. In other embodiments, lengths A, B, E, and F are between 0.5 inches and 5 inches. However, other embodiments with other lengths A, B, E, and F are possible as well. In some embodiments, lengths C and D are 1 inch, and length G is 0.2 inches. In other embodiments, lengths C and D are 2 inches, and length G is 0 inches. In yet other embodiments, lengths C and D are between 0.5 inches and 5 inches, and length G is between 0 inches and 3 inches. However, other embodiments with other lengths C, D, and G are possible as well.

[0070] Overall, it will be recognized that various embodiments of the present disclosure provide numerous advantages with respect to circuit protection, particularly with respect to either harmonic or DC current signals at the ground connections of AC electrical equipment, such as transformers used in power generation or distribution. For example, interrupting DC or quasi-DC neutral current prevents half-cycle saturation in the transformer core, which in turn prevents overheating, damage, or failure of the transformer. Additionally, DC interruption also improves power quality by reducing harmonics that can trip power system relays and cause significant instability and power outages. This significantly prevents tripping of utility power system relays, disconnection of power compensation and other critical components, and thus avoids partial or total collapse of the power grid in the event of a GIC or EMP event. Further advantages include selective, coordinated protection of the entire power grid, or portions thereof.

[0071] The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. [Explanation of symbols]

[0072] 100 Passive transformer neutral interruption system, 12 Transformer, 10 Transformer neutral, 14 Grounding, 110 DC interruption components, 112 Passive overvoltage protection devices, 200 Passive transformer neutral interruption system, 204 Power resistors, 300 Passive transformer neutral interruption system, 310a-n Capacitors, 320a-n Capacitors, 400 Passive transformer neutral interruption system, 402 Neutral current monitoring devices, 406 Voltage measuring devices, 408 Electronic modules, 410 Shielded enclosures, 412 Communication networks, 414 Control rooms, 500 Passive transformer neutral interruption system, 502 Maintenance bypass switches, 504 AC circuit breakers, 600 Passive transformer neutral interruption system, 622 Filters, 624 Sensing electronics, 634 Power input, 650 Electromagnetic detector, 700 Transformer neutral interrupting system, 702 High voltage breaker, 800 Passive OVPD assembly, 801a-c Subassembly, 802a-b Circuit lead, 803a-c Conductor, 804a-b Mount, 805a-b Bottom conductor, 806a-c Spark gap, 807a-b Top conductor, 810a-c Electrode, 814a-b Insulator, 816a-b Cylindrical shield, 900 Passive OVPD assembly, 901a Subassembly, 905a Conductor, 905b Conductor, 906 Spark gap, 907a Conductor, 907b Conductor, 908a Junction, 908b Junction, 915a Cross section, 917a Cross section, 918a Cross section, 918b Cross section

Claims

1. 1. A protection circuit usable in an AC system including a transformer, comprising: a direct current (DC) blocking component electrically connected between the neutral of the transformer and ground; an overvoltage protection device electrically connected in parallel with the DC blocking component, the overvoltage protection device being constructed to repeatedly and reliably provide overvoltage protection in response to a voltage at the transformer neutral point exceeding a threshold; Including, the DC blocking component has an impedance below a predetermined value, thereby effectively grounding the neutral of the transformer; A protection circuit, wherein the DC blocking component remains permanently connected to the transformer neutral during operation of the protection circuit.

2. The protection circuit of claim 1 , wherein the DC blocking component and the overvoltage protector remain connected between the transformer neutral and the ground during operation of the protection circuit.

3. The protection circuit of claim 1 , wherein the protection circuit lacks an automatic switching component capable of automatically disconnecting the DC blocking component and the overvoltage protector from the transformer neutral.

4. The protection circuit of claim 1 , further comprising a power resistor electrically connected in series with the transformer neutral and the DC blocking component.

5. The protection circuit of claim 1 , wherein the DC blocking component comprises a capacitor.

6. The overvoltage protection device is Spark gap, Metal oxide varistors, Silicon carbon varistor, variable resistor, and Surge arresters, 10. The protection circuit of claim 1, comprising at least one device selected from the group consisting of:

7. 10. The protection circuit of claim 1, wherein the overvoltage protector is constructed to operate multiple times in response to the voltage at the transformer neutral exceeding a threshold while maintaining operability within a predetermined range below a withstand voltage of at least one of the transformer and the DC blocking component.

8. 10. The protection circuit of claim 1, wherein the overvoltage protection device comprises a spark gap.

9. The overvoltage protection device is a first conductor and an opposing second conductor, each including an extension that connects to a circuit lead, an electrode region, and an ablation end; a spark gap formed between the electrode region of the first conductor and the electrode region of the second conductor, the protection circuit being electrically connected to the overvoltage protection device and exposed to a potential electrical event having a breakdown voltage below 35,000 volts and a current range greater than 5,000 amperes for at least 40 milliseconds; Including, 2. The protection circuit of claim 1, wherein the spark gap is designed such that for electrical events within the range of possible electrical events, a breakdown voltage across the spark gap is maintained within a predetermined range.

10. The overvoltage protection device is a discharge device having a first breakdown voltage, wherein a first current flows across the spark gap at the first breakdown voltage; 2. The protection circuit of claim 1, comprising:

11. 10. The protection circuit of claim 1, further comprising a voltage measurement device electrically connected between the neutral point of the transformer and ground.

12. further comprising a control circuit connected to the voltage measurement device; the transformer is connected to one or more power line phases, the one or more power line phases connecting the transformer to an electrical grid; 12. The protection circuit of claim 11, wherein in response to a voltage exceeding a threshold for a predetermined time, the control circuit is configured to send an activation signal to activate one or more circuit breakers electrically connected to respective power line phases of the one or more power line phases to electrically disconnect the transformer from the electrical grid.

13. further comprising a control circuit connected to the voltage measurement device; the transformer is connected to one or more power line phases, the power line phases connecting the transformer to an electrical grid; 12. The protection circuit of claim 11, wherein in response to a rate of change of voltage exceeding a predetermined rate of change, the control circuit is configured to send an activation signal to activate one or more circuit breakers electrically connected to respective power line phases of the one or more power line phases to electrically disconnect the transformer from the electrical network.

14. further comprising a control circuit connected to the voltage measurement device; the transformer is connected to one or more power line phases, the one or more power line phases connecting the transformer to an electrical grid; 12. The protection circuit of claim 11, wherein in response to a voltage reaching a threshold detected by the voltage measurement device, the control circuit is configured to send an activation signal to activate one or more circuit breakers electrically connected to the power line phases to electrically disconnect the transformer from the electrical network.

15. 12. The protection circuit of claim 11, wherein the voltage comprises a DC voltage.

16. 10. The protection circuit of claim 1, further comprising a maintenance bypass switch electrically connected between the DC blocking component and the transformer neutral, the maintenance bypass switch operable to disconnect the DC blocking component from the transformer neutral during maintenance.

17. 2. The protection circuit of claim 1, wherein the circuit lacks an electronically controlled switch electrically connected along a path in parallel with the DC blocking component between the transformer neutral and ground that operates during normal operation of the protection circuit.

18. a transformer having one or more connections, each connection associated with a different power line phase of an AC power signal; a DC neutral point interruption circuit electrically connected between the neutral point of the transformer and ground; a voltage measurement device that transmits a signal upon detecting a voltage across the neutral and ground of the transformer; an overvoltage protection device electrically connected in parallel with the DC neutral point interruption circuit between the neutral point of the transformer and ground; at least one breaker electrically connected to a power line phase of the transformer; receiving the signal from the voltage measurement device; and signaling to open the at least one breaker electrically connected to the power line phase of the transformer in response to determining that the voltage across the transformer neutral and ground is greater than or equal to a predetermined threshold. a control circuit configured as follows: Including, An electrical protection system, wherein at a voltage level above the predetermined threshold, an overvoltage protection device is configured to be triggered to discharge the voltage.

19. 20. The electrical protection system of claim 18, wherein the voltage level at which the overvoltage protection device is configured to be triggered to discharge voltage falls below a second voltage level, the second voltage level being a withstand voltage limit of at least one of the DC neutral interruption circuit or a transformer neutral insulator of the transformer.

20. 20. The electrical protection system of claim 18, wherein the DC neutral interruption circuit comprises one of a passive DC neutral interruption circuit or an active DC neutral interruption circuit.

21. A method of protecting a power grid against damage due to induced currents or voltages at the neutral points of power grid transformers within the power grid using an electrical protection system according to any one of claims 18 to 20, comprising: detecting a voltage at a transformer neutral of a first transformer in the power grid having a characteristic indicative of potential damage to circuits contained within the power grid; selecting one or more transformers other than the first transformer in the power grid, the one or more transformers being associated with a phase breaker and a control circuit; sending an operation command to the control circuitry associated with the one or more transformers indicating to the control circuitry to open the phase breakers, thereby disconnecting the one or more transformers and segmenting the power grid; A method comprising:

22. 22. The method of claim 21, further comprising activating a phase breaker associated with the first transformer.

23. 22. The method of claim 21, wherein the one or more transformers are located remotely from an electronic module operable to detect a voltage at the first transformer.

24. 22. The method of claim 21 , wherein selecting the one or more transformers comprises executing an algorithm to select one or more transformers from among a plurality of transformers in the power grid based at least in part on a distance of the one or more transformers from a power plant and a distance between the first transformer and the one or more transformers.

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