Device, system and method for monitoring and reporting line status of zone selective interlocking cables

Abstract

Various embodiments of the present invention relate to a first trip unit configured to be coupled to a power distribution system arranged in a zone selective interlocking (ZSI) arrangement. The first trip unit includes an input / output circuit including a ZSI input terminal and a ZSI output terminal; a heartbeat signaling module, in response to a normal condition, the heartbeat signaling module is configured to transmit a second signal to a second trip unit in a zone at a lower level than the first trip unit; a first monitoring module, in response to a normal condition, the first monitoring module is configured to monitor a first signal received by the first trip unit from a third trip unit in a higher level zone; and a second monitoring module, the second monitoring module is configured to detect a fault condition. Related systems, devices, and methods are also described.

Description

Technical Field

[0001] Various embodiments described herein relate to apparatus, systems, and methods for power distribution systems, and more particularly to monitoring and reporting line status of zone selective interlocking cables. Background Art

[0002] Zone selective interlocking (ZSI), also known as zone interlocking or zone inhibition, is a communication scheme used, for example, with trip units or protection relays to enhance protection in a distribution system under short circuit or ground fault conditions. Enhanced protection can be achieved through communication between trip units or protection relays across different zones. Trip units can trip circuit breakers to prevent overcurrent under short circuit or ground fault conditions. However, trip units in zones other than the short circuit or ground fault may be unnecessarily affected or affected for a longer period of time than warranted by a disconnected or loose wire in a cable in a ZSI arrangement, thereby degrading the performance of the distribution system. Summary of the invention

[0003] Various embodiments of the present invention relate to a first trip unit configured to be coupled to a power distribution system arranged in a zone selective interlocking (ZSI) arrangement. The first trip unit includes an input / output circuit having a ZSI input terminal and a ZSI output terminal. In response to a fault condition including a short circuit or a ground fault in the power distribution system, the ZSI input terminal is configured to an input mode, and in response to a normal condition in which there is no short circuit or ground fault in the power distribution system, the ZSI input terminal is configured to an output mode. In response to the fault condition, the ZSI output terminal is configured to an output mode, and in response to a normal condition, the ZSI output terminal is configured to an input mode. The first trip unit includes a heartbeat signaling module, in response to a normal condition, the heartbeat signaling module is configured to transmit a second signal to a second trip unit in a region of a lower level than the first trip unit; a first monitoring module, in response to a normal condition, the first monitoring module is configured to monitor a first signal received by the first trip unit from a third trip unit in a higher level region; and a second monitoring module, the second monitoring module is configured to detect a fault condition.

[0004] According to various embodiments, in response to receiving the first signal within a predetermined duration, the first monitoring module may be configured to provide a good ZSI cable indication. Upon detecting that the first signal is not received due to a loose or disconnected ZSI cable between the first trip unit and the third trip unit, the first monitoring module may be configured to provide a bad ZSI cable indication. In response to a fault condition, the first trip unit may be configured to receive a third signal from the second trip unit by the first trip unit. The third signal may include a blocking signal having a non-zero voltage. The blocking signal indicates to the first trip unit to avoid tripping before a delay time has elapsed.

[0005] According to various embodiments, the ZSI input terminal may include an open drain output mode with a pull-up resistor that provides a non-zero direct current (DC) voltage in response to a normal condition. The ZSI output terminal may include a pull-up resistor based input mode in response to a normal condition.

[0006] According to various embodiments, the second trip unit may include a self-interlocking jumper configured to couple the ZSI input terminal of the second trip unit with the ZSI output terminal of the second trip unit. When the second trip unit has a fourth trip unit located downstream of the second trip unit, the second trip unit may include a self-interlocking jumper, and the fourth trip unit is not included in the ZSI arrangement. Time-based coordination may be provided between the second trip unit and the fourth trip unit.

[0007] The first signal may be a first heartbeat signal, and the second signal may be a second heartbeat signal. The second trip unit may be configured to send a third heartbeat signal from the ZSI input terminal of the second trip unit to the ZSI output terminal of the second trip unit when the self-interlocking jumper is installed. The second heartbeat signal may be broadcast to one or more lower-level regional trip units including the second trip unit. The first monitoring module may be configured to be able to detect a loose or disconnected ZSI cable after a waiting period of time. The ZSI input terminal and the ZSI output terminal of the first trip unit may be reset periodically. The corresponding ZSI input terminals and ZSI output terminals of the first trip unit, the second trip unit, and the third trip unit may be reset periodically to coordinate signaling and / or detection in the ZSI arrangement.

[0008] Various embodiments of the present invention are directed to a method of operating a first trip unit coupled to a power distribution system. The method includes transmitting a second heartbeat signal to a second trip unit in a zone at a lower level than the first trip unit, monitoring a first heartbeat signal received by the first trip unit from a third trip unit in a zone at a higher level than the first trip unit, and detecting a fault condition including a short circuit or a ground fault in the power distribution system.

[0009] According to various embodiments, the method may include configuring a ZSI input terminal of an input / output circuit to an input mode in response to a fault condition and to an output mode in response to a normal condition without a short circuit or ground fault in the power distribution system, and configuring a ZSI output terminal of the input / output circuit to an output mode in response to a fault condition and to an input mode in response to a normal condition. The method may include selectively providing a good ZSI cable indication in response to receiving the first heartbeat signal within a predetermined duration, and selectively providing a bad ZSI cable indication upon detecting that the first heartbeat signal is not received due to a loose or disconnected ZSI cable between the first trip unit and the third trip unit.

[0010] According to various embodiments, the method may include receiving, by the first trip unit, a blocking signal from the second trip unit in response to a fault condition. The blocking signal instructs the first trip unit to avoid tripping before a delay time has elapsed.

[0011] Various embodiments of the present invention relate to a first electronic device configured to couple with a cable in a power distribution system arranged in a zone selective interlocking (ZSI) arrangement. The first electronic device may include a controller configured to control the first electronic device to transmit a second signal to a second electronic device in a zone at a lower level than the first electronic device. The controller may also be configured to monitor a first signal received by the first electronic device from a third electronic device in a higher level zone. The controller may also be configured to detect a fault condition in the power distribution system including a short circuit or a ground fault.

[0012] According to various embodiments, the first electronic device may include an input / output circuit including a ZSI input terminal and a ZSI output terminal. In response to a fault condition, the ZSI input terminal may be configured to an input mode, and in response to a normal condition in which there is no short circuit or ground fault in the power distribution system, the ZSI input terminal may be configured to an output mode. In response to a fault condition, the ZSI output terminal may be configured to an output mode, and in response to a normal condition, the ZSI output terminal may be configured to an input mode. In response to receiving the first signal within a predetermined duration, the controller may also be configured to selectively provide a good ZSI cable indication, and upon detecting that the first signal is not received due to a loose or disconnected ZSI cable between the first electronic device and the third electronic device, the controller may also be configured to selectively provide a bad ZSI cable indication.

[0013] Those skilled in the art will appreciate other features, advantages and details of the present invention upon reading the following drawings and detailed description of the preferred embodiments, which description is merely exemplary of the present invention.

[0014] It should be noted that the various aspects of the inventive concept described with respect to one embodiment may be combined in different embodiments, although not specifically described. That is, all embodiments and / or features of any embodiment may be combined in any manner and / or combination. Other operations according to any embodiment described herein may also be performed. These and other aspects of the inventive concept are described in detail in the specification set forth below. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 An exemplary power distribution system is shown according to various embodiments described herein.

[0016] Figure 2 The present invention is shown in accordance with various embodiments described herein. Figure 1 An exemplary zone selective interlocking (ZSI) wiring scheme for the distribution system.

[0017] Figure 3A Exemplary ZSI terminals and input / output modes with a heartbeat signal in normal operation are shown according to various embodiments described herein.

[0018] Figure 3B Exemplary ZSI terminals and input / output modes in response to short circuit or ground fault conditions are shown according to various embodiments described herein.

[0019] Figure 4 is a circuit diagram illustrating input / output modes of exemplary ZO and ZI terminals according to various embodiments described herein.

[0020] FIG. 5A to FIG. 5D Exemplary waveforms at the ZO and ZI terminals of a trip unit under various operating conditions are shown according to various embodiments described herein.

[0021] Figure 6 An exemplary zone selective interlocking (ZSI) wiring scheme for a power distribution system is shown in accordance with various embodiments described herein.

[0022] Figure 7 is a block diagram of a trip unit according to various embodiments described herein. DETAILED DESCRIPTION

[0023] Various embodiments will be described more fully below with reference to the accompanying drawings. Other embodiments may take many different forms and should not be construed as being limited to the embodiments set forth herein. The same numerals represent the same elements throughout the text.

[0024] In the accompanying drawings, the relative sizes of regions or features may be exaggerated for clarity. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0025] The distribution system can use a zone selective interlocking (ZSI) line scheme that utilizes a ZSI cable. Circuit breakers and their associated trip units can communicate with each other so that the circuit breaker closest to the fault can clear a short circuit or ground fault in the shortest time. In a typical ZSI system, each circuit breaker can be wired to other circuit breakers via a ZSI input terminal and a ZSI output terminal. If a short circuit or ground fault occurs, the circuit breaker communicates to determine and isolate the location of the fault and attempts to trip or disconnect the nearest circuit breaker. The lines associated with the circuit breakers arranged in a ZSI scheme can be logically divided into multiple areas. Communication between various circuit breakers can allow activation of the circuit breaker closest to the fault (i.e., tripping causes power to be interrupted) while providing communication about the fault event to the upstream circuit breaker. The upstream circuit breaker can avoid tripping unnecessarily for a fault isolated further downstream (i.e., in a lower level area), thereby reducing power outages across higher level areas.

[0026] Lines and / or cables may be deployed, such as twisted pair instrument cables with 16, 18, or 20 gauge (American Wire Gauge) conductors. Twisted pair instrument cables may be used to connect trip units or protection relays from different areas in a power distribution system. For example, twisted pair instrument cables with 16, 18, or 20 gauge conductors are commonly used in the ZSI line scheme described herein. These cables may be installed in metal conduits with other control circuits and may be physically separated from current-carrying power circuits. However, the cables may become disconnected or loose. If not detected, these disconnected or loose cables may result in the inability to quickly localize and clear the fault. Manual inspection and detection by a technician performing an ohmmeter line continuity check may require downtime of the circuit breaker and / or trip unit.

[0027] The various embodiments described herein may arise from the recognition that it may be desirable to monitor ZSI cables to detect disconnected or loose wires in cables arranged in a ZSI in a power distribution system. It is desirable to monitor the cables using existing ZSI line schemes with minimal new hardware and / or wiring. According to the various embodiments described herein, heartbeat signaling and detection may be used without introducing a significant amount of new hardware and / or wiring. Although the various embodiments will be described with respect to a trip unit as a non-limiting example, the concepts of these embodiments may be applied to protective relays and / or any electronic device used with a power distribution system.

[0028] I. ZSI cable line scheme in power distribution system

[0029] Figure 1 An example power distribution system is shown. Figure 1 , the power distribution system may include a distribution transformer 100, a main circuit breaker CB1.1 with its associated trip units in zone 1, feeder circuit breakers CB2.1, CB2.2 and CB2.3 with their associated trip units in zone 2, and branch circuit breakers CB3.1, CB3.2 and CB3.3 with their respective trip units in zone 3. The ZSI line scheme may be used to connect various circuit breakers in and across different zones.

[0030] The commonly used ZSI line solution is the 3-wire solution. Figure 2 Shown for Figure 1 An exemplary zone selective interlocking (ZSI) circuit scheme for the power distribution system of FIG. Each trip unit associated with a circuit breaker may have a ZSI common terminal, a ZSI input terminal, and a ZSI output terminal. Figure 2 , the ZSI common terminal, the ZSI input terminal, and the ZSI output terminal may be referred to as a ZC terminal, a ZI terminal, and a ZO terminal, respectively. The ZC terminal may be ungrounded. ZO and ZI may be terminals that may be configured as input terminals or output terminals based on line conditions. For example, in a short circuit or ground fault condition, the ZO terminal may be configured to output a signal to a trip unit in a higher level area, and the ZI terminal may be configured to receive a signal from a lower level area.

[0031] Still see Figure 2 , in some embodiments, all ZC terminals in the power distribution system can be connected together. In this non-limiting example, the ZO terminals of circuit breakers CB3.1, CB3.2, and CB3.3 in zone 3 can be connected to the ZI terminal of circuit breaker CB2.3 in zone 2. The ZO terminal of circuit breaker CB2.3 in zone 2 can be connected to the ZI terminal of circuit breaker CB1.1 in zone 1. As used herein, a "higher level zone" refers to a zone that is closer to or includes a main circuit breaker, while a "lower level zone" refers to a zone that is farther from the main circuit breaker. For example, Figure 1 and Figure 2 As shown, region 3 is a lower-level region relative to region 2 , and region 1 is a higher-level region relative to region 2 .

[0032] See again Figure 1, when a short circuit or ground fault condition occurs in zone 3, the fault current may exceed a predetermined pick-up level or current threshold of CB3.3, CB2.3 and / or CB1.1. If the predetermined pick-up level or current threshold is exceeded, upon detection, CB3.3 may output a non-zero DC voltage signal that is very different from 0V (e.g., 5.0V) at the ZO terminal of CB3.3, for example. At the same time, CB3.3 may trip to interrupt the fault current and subsequently clear the fault. In the ZSI scheme, the non-zero DC voltage signal may be referred to as a blocking signal or an inhibiting signal. The blocking signal may be transmitted from CB3.3 to CB2.3 to confirm that CB3.3 has identified the fault. The blocking signal may indicate to CB2.3 to avoid tripping to clear the fault before the short circuit or ground fault time delay of CB2.3 has passed. Thus, the short circuit or ground fault is isolated around CB3.3, thereby preventing power interruption at CB2.3 and other circuit breakers in the area lower than CB2.3 (such as those served by CB3.1 and / or CB3.2).

[0033] If the fault current exceeds a predetermined pickup level or threshold of CB2.3, CB2.3 may also output a blocking signal at the ZO terminal of CB2.3. The blocking signal is transmitted to CB1.1 to confirm that CB2.3 has identified the fault. Due to the blocking signal, CB1.1 will not trip to clear the fault before the short circuit or ground fault time delay of CB1.1 has passed. Therefore, the blocking signal received by CB1.1 prevents large-scale power interruptions on Area 1, Area 2, and Area 3. The coordination between the various trips in different areas improves the functionality of the distribution system and reduces power interruptions in the event of a fault in the system. Therefore, as shown in this non-limiting example, the ZSI scheme facilitates rapid fault clearing without interrupting the power supply to the rest of the distribution system. In addition, the coordination of the various trips is not affected.

[0034] Still see Figure 1 and / or Figure 2 , among the circuit breakers in zone 3, only CB3.3 may have downstream circuit breakers. Circuit breakers downstream of CB3.3 may not provide ZSI features, but may still require time-based coordination with CB3.3. Self-interlocking jumpers can be used to achieve this coordination with CB3.3. Figure 23, the self-interlocking jumper is represented by a dashed line between the ZO and ZI terminals of CB3.3. If the self-interlocking jumper is installed, when a short circuit or ground fault condition occurs at a location downstream of CB3.3 in the distribution system, CB3.3 will detect its own blocking signal (i.e., a self-blocking signal) at the ZI terminal. The self-blocking signal prevents CB3.3 from tripping until a separate downstream circuit breaker clears the fault, or the short circuit or ground fault time delay of CB3.3 has elapsed. In this non-limiting example, the self-interlocking jumper is not present in CB3.1 and CB3.2 because these circuit breakers do not have downstream circuit breakers.

[0035] In relation to Figure 1 and Figure 2 In the example discussed, one or both wires in the twisted pair instrument cable between CB3.3 and CB2.3 may become loose or even disconnected without being detected by the user or operator of the distribution system. If the aforementioned short circuit or ground fault condition occurs in area 3, the blocking signal transmitted by CB3.3 may not reach CB2.3 due to the damage of the ZSI cable. Therefore, CB3.3 may trip to clear the fault. However, since there is no blocking signal from CB3.3 (due to the loose or disconnected cable), CB2.3 may also trip to clear the fault. Therefore, even if the distribution system uses the described ZSI scheme, the power supply to area 2 may be interrupted. In other words, due to the loose or disconnected ZSI cable in area 3 near CB3.3, the goal of quickly localizing and clearing the fault in area 3 without interrupting the power supply to area 2 and other loads is not achieved. In a conventional distribution system, the status of the ZSI cable may be unknown or unmonitored during daily operation.

[0036] II.ZSI Cable Line Condition Monitoring

[0037] Various embodiments described herein provide systems, devices, and methods for automatically monitoring and reporting the line status of a ZSI cable. Automatic and continuous monitoring and reporting can provide timely diagnostic information for proper maintenance of the power distribution system, and can protect personnel and equipment on site. A heartbeat signaling and detection scheme can be used to achieve continuous monitoring of the line status of the ZSI cable, and detection of loose or disconnected wires in the ZSI cable during normal operation without short circuit or ground fault conditions. In addition, the heartbeat signaling and detection scheme can allow a tripper with a self-interlocking jumper to determine whether there is a loose or disconnected wire in a ZSI cable connected to another tripper. In addition, a loose connection in a self-interlocking jumper can be detected.

[0038] II-1. Input / output mode of ZSI terminal under normal conditions

[0039] Figure 3AAn exemplary ZSI terminal and input / output mode with a heartbeat signal in normal operation are shown. Figure 3A , circuit breakers CB1.1, CB2.3, and CB3.3 are shown. Circuit breaker CB1.1 may be in zone 1, circuit breaker CB2.3 may be in zone 2, and circuit breaker CB3.3 may be in zone 3, as shown in FIG. Figure 1 and / or Figure 2 As shown in the circuit breakers CB1.1, CB2.2 and CB3.3 associated with the circuit breaker. As described herein, operations involving circuit breakers may include trip units associated with the corresponding circuit breakers. The corresponding trip units may be embedded in the corresponding circuit breakers. By default, for each of the plurality of trip units, the ZO terminal is set to an input mode and the ZI terminal is set to an output mode.

[0040] During normal operation of the power distribution system without a short circuit or ground fault condition (i.e., a normal condition), the ZI terminals of the circuit breakers CB1.1, CB2.3, and CB3.3 are set to an open drain output mode with a pull-up resistor. During normal operation, a trip unit in a higher level region may send a pulse train of alternating VSS and VDD signals from its ZI terminal. As described herein, the pulse train of alternating VSS and VDD may be referred to as a heartbeat signal. The heartbeat signal may be broadcast downstream to the trip units in the lower level regions.

[0041] Still see Figure 3A , circuit breaker CB1.1 may send a heartbeat signal to the ZO terminal of circuit breaker CB2.3 through its ZI terminal. Circuit breaker CB2.3 may send another heartbeat signal to the ZO terminal of circuit breaker CB3.3 through the ZI terminal of circuit breaker CB2.3. Circuit breaker CB3.3 may send another separate heartbeat signal through its ZI terminal. When the self-interlocking jumper is installed between the ZI terminal and the ZO terminal of circuit breaker CB3.3, the ZO terminal of circuit breaker CB3.3 also receives a heartbeat signal from its own ZI terminal. The purpose and / or function of the self-interlocking jumper will be described in further detail in Section II-2 below.

[0042] Still reference Figure 3A , the ZI terminal of CB2.3 (on circuit breaker CB2.3), the ZI terminal of CB3.3, and the ZO terminal of CB3.3 can be connected to the signal bus. When the ZI terminal of circuit breaker CB2.3 is floating, the ZI terminal of circuit breaker CB3.3 can drive the signal bus. When the ZI terminals of circuit breaker CB2.3 and circuit breaker CB3.3 are floating, the pull-up resistor on the signal bus can become effective. When the ZI terminals of circuit breaker CB2.3 and circuit breaker CB3.3 are both floating, the pull-up resistor pulls the signal bus to VDD. The input / output circuit structure and the VSS and VDD signals will be combined Figure 4Further detailed discussion.

[0043] II-2. Input / output mode of ZSI terminal under fault condition

[0044] Figure 3B An exemplary ZSI terminal and input / output mode in response to a short circuit or ground fault condition are shown. A short circuit or ground fault condition of a power distribution system may occur downstream of a given trip unit, such as at Figure 1 The fault current can exceed Figure 1 When a fault current exceeding the predetermined pickup level is detected, the circuit breakers CB1.1, CB2.3 and CB3.3 may switch their corresponding ZO terminals to output mode and their ZI terminals to input mode.

[0045] If the short circuit or ground fault condition still exists in zone 3, circuit breaker CB3.3 may output a blocking signal at the ZO terminal of circuit breaker CB3.3. The blocking signal may be transmitted to circuit breaker CB2.3 through a good ZSI cable to confirm that circuit breaker CB3.3 has identified the fault. Similarly, circuit breaker CB2.3 may output a blocking signal at the ZO terminal of circuit breaker CB2.3. The blocking signal may be transmitted to circuit breaker CB1.1 through a good ZSI cable to confirm that circuit breaker CB2.3 has identified the fault. Circuit breaker CB3.3 then trips to interrupt the fault current and clears the fault in the event of a local power outage. Because circuit breakers CB1.1 and CB2.3 are prevented from tripping by the received blocking signal, the power outage in the distribution system is limited.

[0046] In this ZSI scheme, the purpose of the self-interlocking jumper is to provide coordination with downstream circuit breakers that do not provide the ZSI feature under fault conditions. When the self-interlocking jumper is installed to CB3.3, and when a short circuit or ground fault condition occurs at a location downstream of CB3.3, CB3.3 detects its own blocking signal at the ZI terminal. This self-blocking signal prevents CB3.3 from tripping until a separate downstream circuit breaker clears the fault, or the short circuit or ground fault time delay of CB3.3 has elapsed. The self-interlocking jumper is not present in CB3.1 and CB3.2 because they do not have downstream circuit breakers. In addition, in Figure 3A In the circuit breaker, CB3.3 already has the ZSI feature and is wired to CB2.3 via a ZSI cable. Therefore, the self-interlocking jumper is installed between the ZI terminal and the ZO terminal of the circuit breaker CB3.3, but not between the ZI terminal and the ZO terminal of the circuit breaker CB2.3.

[0047] II-3. Circuit diagram of ZSI terminal

[0048] Figure 4 It is shown Figure 3A and / or Figure 3B Circuit diagram of exemplary input / output modes of a trip unit of FIG. 1 . To provide a default setting, each trip unit may have a ZO terminal set to an input mode with a pull-up. The trip unit may also have a default setting that sets the ZI terminal to an open drain output mode with a pull-up. See FIG. Figure 4 , for the ZO terminal, the input portion 430 can be set to the on state, and the output portion 440 can be set to the off state at the same time. For the ZI terminal, the input portion 430 can be set to the off state, and the output portion 440 can be set to the on state at the same time. The pull-up function of the input can be realized by a pull-up resistor R connected to VDD. VDD is a non-zero DC voltage that is very different from 0V.

[0049] Still see Figure 4 , the ZI terminal in open drain output mode is driven by a metal oxide semiconductor field effect transistor (MOSFET) 420. When MOSFET 420 is turned on, the ZI terminal is pulled to VSS, which is a reference voltage very close to 0V. When MOSFET 420 is turned off, the ZI terminal can remain floating. The input section 430 can use a Schmitt trigger with hysteresis to provide signal conditioning.

[0050] II-4. Heartbeat signaling and detection

[0051] FIG. 5A to FIG. 5D shows the various operating conditions Figure 3A Example waveforms at the ZO and ZI terminals of the trip unit in FIG. Figure 3A Each trip unit in the circuit monitors the ZO terminal and outputs a corresponding heartbeat signal at the ZI terminal. FIG. 5A to FIG. 5D, the heartbeat signal remains at the low voltage value VSS within a predetermined low duration TSS and then changes to the high voltage value VDD within a predetermined high duration TDD. Thus, the heartbeat signal has a period THB = TSS + TDD. The duty cycle of the heartbeat signal is DT = 100% x (TDD / THB). In some embodiments, for valid heartbeat signaling, the duty cycle DT may be greater than 50%. Additionally, to allow for faster detection, THB may need to be very small. For example, TSS and TDD may be empirically selected as 1 millisecond and 3 milliseconds respectively. Thus, for this non-limiting example, THB = 4 milliseconds and DT = 75%. The parameter TA may be defined as a predetermined multiple of the heartbeat signal period such that TA = M × THB. The parameter TB may be defined as a predetermined multiple of TSS such that TB = N × TSS. For effective firmware implementations, it may be useful for both M and N to be integers. Additionally, 1 < N < (TDD / TSS). As a non-limiting example, M and N may be empirically selected as M = 250 and N = 2.

[0052] Still referring to FIG. 5A to FIG. 5D , the trip unit can start monitoring its own ZO terminal at t = T0. If the trip unit does not detect an input heartbeat signal at its ZO terminal within the duration TA, the trip unit can start pulsing an output heartbeat signal at its ZI terminal at t = T0 + TA + TB. If the trip unit detects an input heartbeat signal at its ZO terminal and if the first detected falling edge of the input heartbeat signal is at t = T1, the trip unit resets its ZI terminal and starts pulsing an output heartbeat signal at its ZI terminal at t = T1 + TA + TB.

[0053] The trip unit can start monitoring its own ZO terminal at t = T0. After a very long waiting period, the trip unit can enable detection of a disconnected or loose wire of the ZSI cable. Referring to FIG. 5A to FIG. 5D , the trip unit can enable detection after t = max(T0 + 3 × (TA + TB), T1 + 3 × (TA + TB)), where the function max(·,·) returns the maximum of its arguments. In practice, the trip unit can enable detection after an even longer waiting period. The trip unit can provide the detection result to the user or operator via a user interface and / or a communication channel. Now, specific scenarios regarding the embodiments related to FIG. 5A to FIG. 5D will be discussed.

[0054] See Figure 5A , the trip unit does not detect an input heartbeat signal at its ZO terminal, i.e., a voltage such as VDD is detected at the ZO terminal. In this case, the trip unit indicates to the operator that the trip unit is located in area 1, as in Figure 1CB1.1 of the trip unit, or the ZSI cable connected to the ZO terminal of the trip unit may be disconnected. In addition, the trip unit does not have a self-interlocking jumper, or the self-interlocking jumper is loose.

[0055] See also Figure 5B , the trip unit may detect an input heartbeat signal at its ZO terminal. The input heartbeat signal may be similar to the output heartbeat signal transmitted by the same trip unit from its ZI terminal. In this case, the trip unit indicates to the operator that 1) or 2) is true: 1) The trip unit is located in zone 1, as in Figure 1 1 of the ZO terminal and has a good self-interlocking jumper, or 2) the ZSI cable connected to the ZO terminal may be disconnected, and the trip unit has a good self-interlocking jumper.

[0056] See also Figure 5C , the trip unit can detect an input heartbeat signal at its ZO terminal. The input heartbeat signal may have a signal period THB. In addition, the falling edge of the input heartbeat signal may lead or lag the falling edge duration TB of the output heartbeat signal. In this case, the trip unit can indicate to the operator that the trip unit has a good ZSI cable connected to its ZO terminal. In addition, the trip unit does not have a self-interlocking jumper, or the self-interlocking jumper is loose.

[0057] See also Figure 5D , the trip unit can detect an input heartbeat signal at its ZO terminal. The input heartbeat signal may have a period of THB / 2. In this case, the trip unit can indicate to the operator that the trip unit has a good ZSI cable connected to its ZO terminal and that the trip unit has a good self-interlocking jumper.

[0058] Different trip units in a distribution system may be energized at different times, so that signaling and detection may become unsynchronized across multiple areas. Therefore, it may be necessary to periodically reset the signaling and detection schemes to improve coordination between different areas. For example, each of the multiple trip units may be configured to reset the ZO terminals and ZI terminals every 10 minutes, thereby restarting the signaling and detection schemes. Monitoring and reporting the line status of the ZSI cable can provide timely diagnostic information for proper maintenance and ultimately help protect personnel and equipment on site. Therefore, periodic or continuous monitoring provides significant advantages in the efficient operation of the distribution system.

[0059] Figure 6An exemplary zone selective interlocking (ZSI) circuit scheme for a power distribution system is shown. A first trip 610 may be in zone 2 of the power distribution system. A third trip 640 may be in zone 1, which is considered a higher level zone in the arrangement of the power distribution system. A second trip 620 is in zone 3, which is considered a lower level zone in the arrangement of the power distribution system than zones 1 and 2. A fourth trip 630 is located downstream of the second trip 620 and does not provide a ZSI feature. The trips 610 may correspond to Figure 3A The circuit breaker CB2.3. The trip unit 620 may correspond to Figure 3A The circuit breaker CB3.3. The trip unit 640 may correspond to Figure 3A Circuit breaker CB1.1.

[0060] The trip unit 610 may include an input / output circuit having a ZSI input terminal and a ZSI output terminal. The modes of the ZSI input terminal and the ZSI output terminal may be changed dynamically. In response to a fault condition (such as a short circuit or ground fault in the power distribution system), the ZSI input terminal may be configured as an input mode. In response to a normal condition in which there is no short circuit or ground fault in the power distribution system, the ZSI input terminal may be configured as an output mode. In response to a fault condition, the ZSI output terminal may be configured as an output mode, and in response to a normal condition, the ZSI output terminal may be configured as an input mode.

[0061] In some embodiments, under normal conditions, the trip unit 640 may send a first signal, such as a first heartbeat signal, to the trip unit 610. The trip unit 610 may transmit a second signal, such as a second heartbeat signal, to the trip unit 620 and / or to a trip unit 630 in a region at a lower level than the trip unit 610. The first monitoring module of the trip unit 610 may monitor the first signal received by the trip unit 610 from the trip unit 640. If the first signal is not detected, or the first signal has a predetermined relationship with respect to the second signal, or the first signal has a predetermined period, the trip unit 610 may determine the state of the ZSI cable. In some embodiments, the state of the ZSI cable may indicate that a cable disconnection or a loose cable has occurred. The trip unit 610 may provide an indication to a user or operator through a user interface and / or through a wired or wireless communication network to indicate whether a cable disconnection or a loose cable has occurred. In some embodiments, the trip unit 610 may include a second monitoring module to detect a fault condition, such as a short circuit or a ground fault in the power distribution system.

[0062] Figure 7700 is a block diagram of a trip unit according to various embodiments described herein. An electronic device (such as a trip unit 700) is configured to couple with a cable 760 in a power distribution system arranged in a zone selective interlocking (ZSI) arrangement. The trip unit 700 may include, physically or logically connected to or embedded in a module in a circuit breaker and / or other device, or co-located with a module in a circuit breaker and / or other device, or a module in a circuit breaker and / or other device. The trip unit 700 includes a controller 750 and an input / output circuit 740. The controller 750 may include a heartbeat signaling module 710, a first monitoring module 720, and / or a second monitoring module 730. The controller 750 may include one or more processors to perform the operations described herein. The controller 750, the heartbeat signaling module 710, the first monitoring module 720, and / or the second monitoring module 730 may be implemented using software, hardware, or a combination thereof. The trip unit 700 may be coupled with a cable 760 for connecting an entity (such as a circuit breaker in a power distribution system). The trip unit includes a heartbeat signaling module 710, which is configured to transmit a second signal (such as a second heartbeat signal) to a second trip unit in a region at a lower level than the first trip unit. In response to a normal condition in which there is no short circuit or ground fault in the power distribution system, the first monitoring module 720 is configured to monitor a first signal received by the first trip unit from a third trip unit in a higher level region, such as a first heartbeat signal. The second monitoring module 730 is configured to detect a fault condition with a short circuit or ground fault in the power distribution system. The input / output circuit 740 may include a ZSI input terminal and a ZSI output terminal. The controller 750 may be configured to control the trip unit 700 to transmit a second signal (such as a second heartbeat signal) to a second trip unit in a region at a lower level than the first trip unit.

[0063] According to various embodiments described herein, monitoring ZSI cables to detect disconnected or loose ZSI cables in a power distribution system improves system performance while reducing power outages within the power distribution system. Heartbeat signaling and detection are used without introducing a large amount of new hardware and / or wiring. According to various embodiments described herein, trip units with downstream (i.e., lower level area) trip units and trip units without lower level area trip units monitor and detect disconnected or loose ZSI cables.

[0064] Further definition :

[0065] In the above description of various embodiments of the present disclosure, it should be understood that the terms used herein are only used for the purpose of describing specific embodiments, and are not intended to limit the present invention. Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meanings commonly understood by those of ordinary skill in the art to which the present disclosure belongs. It should also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having the same meaning as their meanings in the context of this specification and related fields, and unless clearly defined herein, will not be interpreted in an idealized or overly formalized sense.

[0066] When an element is referred to as "connected", "connected", "responsive (to)" or its variant to another element, the element may be directly connected, coupled or responsive to another element, or there may be an intermediate element. On the contrary, when an element is referred to as "directly connected", "directly coupled", "directly responsive (to)" or its variant to another element, there is no intermediate element. The same number represents the same element throughout the text. In addition, "coupled", "connected", "responsive to" or its variant as used herein may include wireless coupling, connection or response. Unless the context clearly indicates otherwise, as used herein, the singular forms "one", "one", "a kind of" and "the" are intended to also include plural forms. For the sake of simplicity and / or clarity, well-known functions or structures may not be described in detail. The term "and / or" includes any and all combinations of one or more associated listed items. The expression after the element list (such as "at least one of ......") modifies the entire element list and does not modify the individual elements in the list.

[0067] It should be understood that although the terms "first", "second", "third", etc. may be used herein to describe different elements, these elements should not be limited by these terms; on the contrary, these terms are only used to distinguish one element from another element. Therefore, without departing from the scope of the present invention, the first element discussed may be referred to as the second element.

[0068] As used herein, the terms "comprises," "including," "contains," "containing," "having," or variations thereof are open ended and include one or more stated features, integers, elements, steps, parts, or functions, but do not preclude the presence or addition of one or more other features, integers, elements, steps, parts, or groups thereof.

[0069] Exemplary embodiments are described herein with reference to block diagrams and / or flowchart illustrations of computer-implemented methods, devices (systems and / or apparatuses), and / or computer program products. It should be understood that the blocks in the block diagrams and / or flowchart illustrations and the combination of blocks in the block diagrams and / or flowchart illustrations can be implemented by computer program instructions executed by one or more computer circuits. These computer program instructions can be provided to processor circuits of general-purpose computer circuits, special-purpose computer circuits, and / or other programmable data processing circuits to produce a machine, so that the processor of the computer and / or other programmable data processing devices execute instructions to transform and control transistors, values ​​stored in memory locations, and other hardware components in such circuits to implement the functions / actions specified in the block diagrams and / or flowcharts, thereby creating means (functions) and / or structures for implementing the functions / actions specified in the block diagrams and / or flowcharts.

[0070] These computer program instructions may also be stored in a tangible computer-readable medium that can instruct a computer or other programmable data processing device to function in a specific manner so that the instructions stored in the computer-readable medium produce an article of manufacture including instructions for implementing the functions / actions specified in the block diagram and / or flowchart block.

[0071] Tangible, non-transitory computer-readable media may include electronic, magnetic, optical, electromagnetic or semiconductor data storage systems, devices or apparatuses. More specific examples of computer-readable media would include the following: portable computer diskettes, random access memory (RAM) circuits, read-only memory (ROM) circuits, erasable programmable read-only memory (EPROM or flash memory) circuits, portable compact disk read-only memory (CD-ROM) and portable digital video disk read-only memory (DVD / BluRay).

[0072] Computer program instructions may also be loaded onto a computer and / or other programmable data processing device so that a series of operational steps are performed on the computer and / or other programmable device to produce a computer-implemented process so that the instructions executed on the computer or other programmable device provide steps for implementing the functions / actions specified in the block diagram and / or flowchart blocks. Thus, embodiments of the present disclosure may be embodied in hardware and / or software (including firmware, resident software, microcode, etc.) running on a processor such as a digital signal processor (which may be collectively referred to as a "circuit," "module," or variations thereof).

[0073] The flow charts and block diagrams in the accompanying drawings illustrate the possible specific implementation architecture, functions and operations of the system, method and computer program product according to various aspects of the present disclosure. In this regard, each box in the flow chart or block diagram may represent a module, segment or part of the code, which includes one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative specific implementations, the functions indicated in the box may not occur in the order indicated in the accompanying drawings. For example, the two boxes shown in succession can actually be executed substantially simultaneously, or these boxes can sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flow chart illustration, and the combination of the boxes in the block diagram and / or flow chart illustration can be implemented by a system based on dedicated hardware that performs a specified function or action, or a combination of dedicated hardware and computer instructions.

[0074] It should also be noted that in some alternative implementations, the function / action indicated in the frame may not occur in the order indicated in the flow chart. For example, two frames shown in succession can actually be performed substantially simultaneously, or these frames can sometimes be performed in reverse order, depending on the function / action involved. In addition, the function of a given frame of a flow chart and / or block diagram can be divided into multiple frames, and / or the function of two or more frames of a flow chart and / or block diagram can be integrated at least in part. Finally, other frames can be added / inserted between the frames shown. In addition, although some figures include arrows on the communication path to show the main direction of communication, it should be understood that communication can occur in the direction opposite to the arrows depicted.

[0075] Many different embodiments have been disclosed herein in conjunction with the above description and the accompanying drawings. It should be understood that it is excessively repetitive and confusing to literally describe and illustrate each combination and sub-combination of these embodiments. Therefore, this specification (including the accompanying drawings) should be understood to constitute a complete written description of various exemplary combinations and sub-combinations of the embodiments and the ways and processes of making and using them, and should support claims to any such combination or sub-combination. Many variations and modifications may be made to the embodiments without substantially departing from the principles of the invention. All these changes and modifications are intended to fall within the scope of the invention.

Claims

1. A first trip unit, the first trip unit being configured to be coupled to a power distribution system arranged in a zone selective interlocking (ZSI) arrangement, the first trip unit comprising: an input / output circuit comprising a ZSI input terminal and a ZSI output terminal, wherein in response to a fault condition including a short circuit or a ground fault in the power distribution system, the ZSI input terminal is configured in an input mode, and in response to a normal condition without the short circuit or the ground fault in the power distribution system, the ZSI input terminal is configured in an output mode, and wherein in response to the fault condition, the ZSI output terminal is configured in an output mode, and in response to the normal condition, the ZSI output terminal is configured in an input mode; a heartbeat signaling module, in response to the normal condition, the heartbeat signaling module being configured to transmit a second signal to a second trip unit in a region at a lower level than the first trip unit; a first monitoring module, responsive to the normal condition, the first monitoring module being configured to monitor a first signal received by the first trip unit from a third trip unit in a higher level zone; and a second monitoring module, the second monitoring module being configured to detect the fault condition, wherein the second release comprises a self-interlocking jumper, and wherein the self-interlocking jumper is configured to directly couple the ZSI input terminal of the second trip unit to the ZSI output terminal of the second trip unit; and The second release is configured to send a heartbeat signal from a ZSI input terminal of the second release to a ZSI output terminal of the second release when the self-interlocking jumper is installed.

2. The first release according to claim 1, Wherein in response to receiving the first signal within a predetermined duration, the first monitoring module is configured to provide a good ZSI cable indication.

3. The first release according to claim 1, The first monitoring module is configured to provide a bad ZSI cable indication upon detecting that the first signal is not received due to a loose or disconnected ZSI cable between the first trip unit and the third trip unit.

4. The first release according to claim 1, wherein in response to the fault condition, the first trip unit is configured to receive a third signal from the second trip unit by the first trip unit, The third signal comprises a blocking signal having a non-zero voltage.

5. The first release according to claim 4, The blocking signal indicates to the first trip unit to avoid tripping before a delay time has elapsed.

6. The first release according to claim 1, Wherein when the second release has a fourth release located downstream of the second release, the second release includes the self-interlocking jumper, and The fourth trip unit is not included in the ZSI arrangement.

7. The first release according to claim 1, The first signal includes a first heartbeat signal, wherein the second signal comprises a second heartbeat signal, and The second release is configured to send a third heartbeat signal from a ZSI input terminal of the second release to a ZSI output terminal of the second release when the self-interlocking jumper is installed.

8. The first release according to claim 1, wherein the first signal comprises a first heartbeat signal, and The second signal includes a second heartbeat signal, and the second heartbeat signal is broadcast to one or more lower-level area trip units including the second trip unit.

9. The first release according to claim 1, The first monitoring module is configured to detect a loose or disconnected ZSI cable after a waiting period.

10. The first release according to claim 1, The ZSI input terminal and the ZSI output terminal of the first trip unit are periodically reset, and in response to the periodic reset, the ZSI input terminal and the ZSI output terminal of the second trip unit coupled to the power distribution system arranged in the ZSI arrangement and the ZSI input terminal and the ZSI output terminal of the third trip unit are periodically reset to coordinate signaling and / or detection in the ZSI arrangement.

11. A method of operating a first trip unit coupled to a power distribution system arranged in a zone selective interlocking (ZSI) arrangement, the method comprising: transmitting a second heartbeat signal to a second trip unit in a region lower in level than the first trip unit; monitoring a first heartbeat signal received by the first trip unit from a third trip unit in a zone at a higher level than the first trip unit; as well as Detecting fault conditions including short circuits or ground faults in the power distribution system wherein the second trip unit includes a self-interlocking jumper configured to directly couple the ZSI input terminal of the second trip unit to the ZSI output terminal of the second trip unit; The second release is configured to send a third heartbeat signal from a ZSI input terminal of the second release to a ZSI output terminal of the second release when the self-interlocking jumper is installed.

12. The method according to claim 11, further comprising: configuring a ZSI input terminal of an input / output circuit to an input mode in response to the fault condition, and configuring the ZSI input terminal to an output mode in response to a normal condition in the power distribution system without the short circuit or the ground fault; as well as A ZSI output terminal of the input / output circuit is configured to an output mode in response to the fault condition, and the ZSI output terminal is configured to an input mode in response to the normal condition.

13. The method according to claim 11, further comprising: selectively providing a good ZSI cable indication in response to receiving the first heartbeat signal within a predetermined duration; as well as A bad ZSI cable indication is selectively provided upon detecting that the first heartbeat signal is not received due to a loose or disconnected ZSI cable between the first trip unit and the third trip unit.

14. The method according to claim 11, further comprising: In response to the fault condition, receiving, by the first trip unit, a blocking signal from the second trip unit, The blocking signal indicates to the first trip unit to avoid tripping before a delay time has elapsed.

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