Solid-state circuit breaker with solid-state interlocking mechanism

Abstract

A system includes a first circuit breaker (10B-10N) comprising a first solid-state breaker (100), first mechanical contacts (500A), and a current sensor structured to detect current flowing through the first circuit breaker, and a second circuit breaker (10A) electrically coupled to the first circuit breaker (10B-10N) and structured to interrupt current flowing to the first circuit breaker, wherein the first circuit breaker (10B-10N) is structured to transmit a request (SSI REQUEST SIGNAL) to the second circuit breaker (10A) upon detecting a fault mode of the first solid-state breaker (100), and wherein the second circuit breaker (10A) is structured to interrupt current flowing to the first circuit breaker (10B-10N) in response to receiving the request.and the first circuit breaker (10B-10N) is further structured to open the first mechanical contacts (500A) when the current flowing through the first circuit breaker (10B-10N) drops to a predetermined level.

Description

Solid-state circuit breaker with solid-state interlocking mechanism BACKGROUND Field The concept disclosed generally refers to circuit breakers and, in particular, to circuit breakers with a solid-state interlocking mechanism. Background information Circuit breakers, such as circuit breakers, are typically used to protect electrical circuits from damage due to overcurrent conditions, such as overloads, short circuits, or other fault conditions, such as arcing or ground faults. Solid-state circuit breakers use solid-state components, such as semiconductor devices, to switch current flowing from a power source to a load on and off. Solid-state circuit breakers can offer advantages over conventional mechanical circuit breakers, such as faster interruption, smaller size, or improved reliability. EP 1529328 A1 discloses a system as defined in the preamble of claim 1. US 2017 / 187179 A1 discloses a junction box configured to be placed between a DC power supply and a load. The junction box includes a first mechanical relay configured to be connected to a positive terminal of the DC power supply, a second mechanical relay configured to be connected to a negative terminal of the DC power supply, a semiconductor relay connected in series to at least one of the first mechanical relay and the second mechanical relay, and a controller that controls the operation of the first mechanical relay, the second mechanical relay, and the semiconductor relay, respectively. When an abnormal condition occurs, the controller controls the first and second mechanical relays to turn them off, and then controls the semiconductor relay to turn it off. Furthermore, WO 2011 / 157306 A1 discloses a circuit breaker failure protection system for a high-voltage direct current (HVDC) circuit breaker positioned to interrupt a DC circuit upon receiving a trip signal. The protection system comprises a current sensor, at least one inductor, and a circuit breaker failure detection unit. The circuit breaker failure detection unit is positioned to assess, based on the measured current, whether the circuit breaker has failed and, if so, to send a trip signal to an adjacent circuit breaker. UL 489I is the requirements scheme for the investigation of solid-state molded-case circuit breakers. It must be used in conjunction with UL 489, which is the safety standard for molded-case circuit breakers, molded-case switches, and circuit breaker enclosures. The scope of UL 489I covers solid-state molded-case circuit breakers rated up to 1000 Vac and 1500 Vdc that switch using semiconductors and have an integral air gap to provide isolation. Semiconductor devices are known to have leakage current, so an air gap is still required to provide galvanic isolation to the load. Mechanical contacts are commonly used to create this air gap. One advantage a solid-state circuit breaker has over a traditional circuit breaker is the size of its air gap. The solid-state breaker can use a much smaller air gap and doesn't require arc-quenching chambers, as the energy is dissipated within the semiconductor device itself. The breaker's reliability relies on the semiconductor's ability to interrupt the current before creating the air gap. However, one of the failure modes of a solid-state component, such as a semiconductor device, is short-circuiting. When such a short-circuit failure occurs, the solid-state circuit breaker will not be able to open. Such a failure to trip the circuit breaker can be detrimental to the solid-state circuit breaker, the circuit interruption system that includes the failed solid-state circuit, and the load. There is room for improvement in solid-state circuit breakers and in systems that include solid-state circuit breakers. SUMMARY These and other needs are met by embodiments of the present invention in which a solid-state circuit breaker in a fault mode requests an upstream circuit breaker to interrupt the current flowing to it so that it can open its mechanical contacts. One aspect of the present invention is a system as defined in claim 1.The system comprises: a first circuit breaker comprising a first solid-state switch, first mechanical contacts, and a current sensor structured to detect current flowing through the first circuit breaker, the first mechanical contacts being coupled in series to the first solid-state switch in a path of the detected current; and a second circuit breaker electrically coupled to the first circuit breaker, disposed upstream of the first circuit breaker, wherein the first circuit breaker is structured to transmit a request to the second circuit breaker upon detecting a fault mode, the fault mode comprising a failure to open the first solid-state switch of the first circuit breaker, and wherein the second circuit breaker is structured to interrupt current flowing to the first circuit breaker in response to receiving the request.According to the present invention, the first circuit breaker is further structured to open the first mechanical contacts when the current flowing through the first circuit breaker decreases to a predetermined level due to interruption, wherein the second circuit breaker is structured to open to interrupt the current flowing to the first circuit breaker in response to receiving a request from the first circuit breaker, wherein the first circuit breaker is further structured to transmit a clear request to the second circuit breaker when the first mechanical contacts have opened, and the second circuit breaker is structured to close to stop the current flowing to the first circuit breaker in response to receiving the clear request from the first circuit breaker. Another aspect of the present invention is a method as defined in claim 6. The method comprises: detecting a failure mode by means of a first circuit breaker, the failure mode comprising a failure to open a first solid-state switch of the first circuit breaker, the first circuit breaker comprising the first solid-state switch, first mechanical contacts, and a current sensor structured for detecting current flowing through the first circuit breaker, the first mechanical contacts being coupled to the first solid-state switch in series in a path of the detected current; transmitting, by means of the first circuit breaker, a request to a second circuit breaker; receiving the request by means of the second circuit breaker; interrupting, by means of the second circuit breaker, the current flowing to the first circuit breaker in response to receiving the request;To detect that the current flowing through the first circuit breaker has decreased to a predetermined level; to open, by means of the first circuit breaker, mechanical contacts in response to detecting that the current flowing through the first circuit breaker has decreased to the predetermined level; to transmit, by means of the first circuit breaker, a clear request to the second circuit breaker when the mechanical contacts have opened; and to stop interrupting the current flowing to the first circuit breaker by means of the second circuit breaker in response to receiving the clear request. BRIEF DESCRIPTION OF THE DRAWINGS; A complete understanding of the present invention can be obtained from the following description of preferred embodiments when read together with the accompanying drawings in which: Figure 1 is a diagram of a solid-state circuit breaker according to an exemplary embodiment of the present invention; Figure 2 is another diagram of a system according to an exemplary embodiment of the present invention; Figure 3 illustrates the waveforms of the current flowing through the circuit breakers according to an exemplary embodiment of the present invention; Figure 4 is a flowchart of a solid-state interlocking method according to an exemplary embodiment of the present invention; and Figure 5 is another flowchart of a solid-state interlocking method according to an exemplary embodiment of the present invention. DESCRIPTION OF PREFERRED EMBODIMENTS Directional phrases used herein, such as, for example, left, right, front, back, up, down and their derivatives, refer to the orientation of the elements shown in the drawings and do not limit the claims unless explicitly stated therein. As used herein, the statement that two or more parts are "coupled" together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. Figure 1 is a diagram of a solid-state circuit breaker 10 according to an exemplary embodiment of the present invention. The solid-state circuit breaker 10 may be part of a larger system that includes additional circuit breakers, solid-state and / or mechanical circuit breakers, such as the system shown in Figure 2. The solid-state circuit breaker 10 is structured to be electrically connected between a power supply and a load 12 via the LINE and LOAD conductors 2, 4. An upstream circuit breaker may be arranged between the power supply and the solid-state circuit breaker 10. The solid-state circuit breaker 10 is structured to open by tripping or by switching to interrupt the current flowing to the load 12 in the event of a fault condition (e.g., without limitation, an overcurrent condition) to protect the load 12, the circuit associated with the load 12, as well as the components within the solid-state circuit breaker 10. The solid-state circuit breaker 10 includes a solid-state switch 100, an electronic trip unit 200, an operating mechanism 300, a sensor 400, and mechanical contacts 500. The solid-state switch 100 includes solid-state switching elements (e.g., without limitation, metal-oxide-semiconductor field-effect transistors (MOSFETs), insulated-gate bipolar transistors (IGBTs)) that are structured to turn on and off (i.e., open and close) to permit or interrupt current flowing to the load 12. The solid-state switch 100 is electrically coupled to the load 12 and the electronic trip unit 200. The electronic trigger unit 200 is structured to control the solid-state switch 100 to open and close and also controls the operating mechanism 300 to open the mechanical contacts 500 upon triggering, based on a signal from sensor 400. The electronic trigger unit 200 may include a processing unit, which may include a processor and memory. The processor may be, for example and without limitation, a microprocessor, a microcontroller, or another suitable processing device or circuit. The memory may be any one or more of a variety of internal and / or external storage media types, such as, without limitation, RAM, ROM, EPROM, EEPROM, FLASH, and the like, which provide a storage register, i.e., a machine-readable medium for data storage, as in the style of an internal storage area of ​​a computer, and may be volatile or non-volatile memory.The memory can store a firmware solution for solid-state interlocking (SSI) where a first solid-state circuit breaker, for example, a downstream circuit breaker, fails to open its solid-state switch, for example, due to a short circuit in another solid-state switch within it. The SSI is implemented by the first solid-state circuit breaker and a second circuit breaker, for example, an upstream circuit breaker. The second circuit breaker may or may not be a solid-state circuit breaker. An SSI-enabled downstream circuit and an SSI-enabled upstream circuit breaker can monitor and respond together to the interrupting capacity of their power semiconductors. SSI is discussed further with reference to Figure 2. The electronic trip unit 200 is structured to determine a fault condition (for example, without limitation, an overcurrent fault) and control the solid-state switch 100 to open in response to the fault condition. Opening the solid-state switch 100 interrupts the current flowing to load 12. The operating mechanism 300 is structured to open the mechanical contacts 500 in response to a signal from the electronic trip unit 200. Opening the mechanical contacts 500 provides galvanic isolation between the power supply and the load 12. For example, and without limitation, the operating mechanism 300 is structured to open the mechanical contacts 500 by moving a movable arm to separate them. The electronic trip unit 200 is structured to control the operating mechanism 300 to open the mechanical contacts 500 only after the solid-state switch 100 has opened to interrupt the current flowing through the solid-state circuit breaker 10.In some exemplary embodiments, the mechanical contacts 500 are not designed to interrupt a rated current flowing through the solid-state circuit breaker 10, and the solid-state circuit breaker 10 may lack components, such as an arc-quenching chamber, to deal with the effects of the mechanical contacts 500 interrupting a rated current. Therefore, the mechanical contacts 500 should only open when the current flowing through the solid-state circuit breaker 10 has decreased to a level where it is safe to open the mechanical contacts 500. The sensor 400 can be a current sensor (e.g., without limitation, a current transformer, a Hall effect sensor, etc.) structured to detect the current flowing through the solid-state circuit breaker 10. The output of the sensor 400 can be provided to the electronic trip unit 200. The electronic trip unit 200 is designed to detect a failure mode of the solid-state circuit breaker 10. The failure mode is a failure of the solid-state circuit breaker 100 to open. In response to the detection of this failure mode, the electronic trip unit 200 is designed to send a request to an upstream circuit breaker. In response to this request, the upstream circuit breaker is designed to interrupt the current flowing to the solid-state circuit breaker 10, resulting in a decrease in the current flowing through the solid-state circuit breaker 10. The electronic trip unit 200 is designed to monitor the current flowing through the solid-state circuit breaker 10 while it is decreasing and to determine when the current has decreased to a predetermined level.The default level is a level at which it is safe to open the mechanical contacts 500. An example of a default level is 5A. However, the default level can be modified without departing from the scope of the present invention. Once the current reaches the default level, the electronic trip unit 200 controls the operating mechanism 300 to open the mechanical contacts 500. After the mechanical contacts 500 open, the electronic trip unit 200 sends a clear request to the upstream circuit breaker. The clear request indicates that the upstream circuit breaker can stop interrupting the current flowing to the solid-state circuit breaker 10. The decrease in current flowing through the solid-state circuit breaker 10 allows the mechanical contacts 500 to open safely.The clear request allows the upstream circuit breaker to quickly restore power, minimizing interruption to other loads downstream of the upstream circuit breaker. In some exemplary embodiments, the interruption duration can be on the order of microseconds and will have little effect on other loads downstream of the upstream circuit breaker. Figure 2 is a diagram of a system 1 according to an exemplary embodiment of the present invention. The system 1 may include one or more solid-state circuit breakers 10. In Figure 2, the system 1 includes a plurality of circuit breakers, for example, an upstream circuit breaker 10A and downstream solid-state circuit breakers 10B-N, where N is an integer. The upstream circuit breaker 10A may or may not be a solid-state circuit breaker. The 10A-N circuit breakers are electrically coupled to each other and communicate with each other via any suitable communication protocol. For example, the 10A-N circuit breakers can be configured to communicate via wired or wireless communication. In wired communication, the 10A-N circuit breakers can communicate via power line communication or control lines. It will be appreciated that any suitable method of communication can be employed between the 10A-N circuit breakers without departing from the scope of the present invention. The 10A-N circuit breakers can communicate with each other to, for example, request or perform a solid-state interlock (SSI) when a fault mode is detected, such as a failure to open a solid-state switch, and one or more of the solid-state circuit breakers fail to open.For example, if a solid-state switch 100 of a downstream solid-state circuit breaker 10B experiences a 100A short circuit, the solid-state switch 100 of the downstream solid-state circuit breaker 10B may fail to open. When the solid-state switch 100 fails to open and current continues to flow through the downstream solid-state circuit breaker 10B, it is unsafe to open the 500A mechanical contacts. In response to the fault mode, the downstream circuit breaker 10B transmits a request (for example, an SSI request) to the upstream circuit breaker 10A. SSI is both a hardware and firmware solution for one of the failure modes associated with the power semiconductor devices in a solid-state circuit breaker. SSI provides a firmware solution that establishes a communication scheme, enabling an upstream circuit breaker to recognize and respond to a downstream circuit breaker experiencing a specific failure mode—for example, when the solid-state circuit breaker is unable to open during a short-circuit event. For instance, when an SSI-enabled solid-state circuit breaker detects a short-circuit fault in one or more of its semiconductor devices, it sends an SSI request to the nearest upstream circuit breaker, which then responsibly interrupts the current flowing to the downstream circuit breaker.The SSI request may indicate a failure to open the solid-state switch of downstream circuit breaker 10B and request upstream circuit breaker 10A to interrupt the current flowing to downstream circuit breaker 10B. SSI can be performed through interrupt logic embedded in the circuit breakers. The downstream circuit breaker 10B is designed to monitor the decrease in current due to interruption and then open its 500A mechanical contacts when the current reaches a predetermined level. This predetermined level can be a current level at which the mechanical contacts of the requesting circuit breaker can safely open in all phases. The upstream circuit breaker 10A interrupts the current flowing to the downstream circuit breaker 10B by temporarily switching off its semiconductor device, such as a SiC MOSFET, IGBT, etc. The duration of the current interruption by the upstream circuit breaker can be adjusted to minimize the impact on other loads downstream of the upstream circuit breaker 10A. The current zero-crossing duration can be measured in microseconds (µs).In examples where the upstream circuit breaker is a non-solid-state circuit breaker (non-SSCB), the upstream non-SSCB circuit breaker can interrupt the current by opening its mechanical contacts. As such, the non-SSCB may also require additional action to reclose. In some exemplary embodiments, however, the non-SSCB may be able to reclose its mechanical contacts. Once the current is interrupted, the downstream solid-state circuit breaker 10B detects the decrease in current flowing through it, reaching a predetermined level via a current sensor (e.g., current sensor 400 described with reference to Figure 1), and opens its mechanical contacts 500A. By opening the mechanical contacts 500A, the downstream circuit breaker 10B can send a clear request to the upstream circuit breaker 10A. This clear request indicates that the fault mode is now remedied; for example, the mechanical contacts of the downstream circuit breaker 10B are now open, and therefore it is clear that the upstream circuit breaker 10A can terminate the SSI mechanism and resume normal operation. Upon receiving a clear request, the 10A upstream circuit breaker can terminate the SSI, for example, by closing its mechanical contacts or solid-state switch. The 10A upstream circuit breaker then resumes normal operation. Figure 3 includes waveforms for the current flowing through downstream and upstream circuit breakers according to an exemplary embodiment of the present invention. A is a waveform for the current flowing through a downstream circuit breaker, for example, a downstream SSI-enabled solid-state circuit breaker. B is a waveform for the current flowing through an upstream circuit breaker, for example, an upstream SSI-enabled circuit breaker. At time t1, both the downstream and upstream circuit breakers are closed. Subsequently, at time t1 and before time t2, a failure mode (i.e., a failure to open the solid-state switch) occurs in the downstream circuit breaker. The downstream circuit breaker detects this failure mode. At time t2, the downstream circuit breaker transmits a request to the upstream circuit breaker. In response to the request, the upstream circuit breaker interrupts the current flowing to the downstream circuit breaker, causing the current flowing through the downstream circuit breaker to decrease. The downstream circuit breaker then waits for the current through it to decrease to a predetermined level where it is safe to open its mechanical contacts. At time t3, the current flowing through the downstream circuit breaker reaches the predetermined level. In one example, the predetermined level might be 5 A or less for a 100 A solid-state circuit breaker. However, it will be appreciated that other predetermined levels can be used without departing from the scope of the present invention. At time t3, the downstream flow can begin the process of opening its mechanical contacts. Since this process takes some time, the mechanical contacts may not actually open until t4. Once the mechanical contacts are open, the downstream circuit breaker sends a clear request to the upstream circuit breaker, indicating that the upstream circuit breaker can stop interrupting the current flowing into the downstream circuit breaker. At time t5, the upstream circuit breaker can receive the clear request from the downstream circuit breaker and stop the current interruption to the downstream circuit breaker, for example, by closing its solid-state switch or mechanical contacts. Between time t5, when the upstream circuit breaker stops interrupting the current, and time t6, the current flowing through the upstream circuit breaker rises to its normal level, which it reaches at time t6. Figure 4 is a flow diagram for a method 400 according to an exemplary embodiment of the present invention. The method can be implemented by an upstream circuit breaker and a downstream circuit breaker and respective processing units as described with reference to Figures 1-3. In 410, the first circuit breaker detects a fault mode (i.e., a failure to open the solid-state switch). The first circuit breaker may be a downstream circuit breaker as described with reference to Figure 2. A request may indicate a failure to open the solid-state breaker of the first circuit breaker and request the second circuit breaker to interrupt the current flowing to the first circuit breaker. At 420, the first circuit breaker transmits the request to a second circuit breaker. The second circuit breaker may be an upstream circuit breaker, as described with reference to Figure 2. There may be one or more upstream circuit breakers within the circuit breaker, and the downstream circuit breaker transmits the SSI request signal to the nearest upstream circuit breaker. The upstream circuit breaker may be a solid-state or non-solid-state circuit breaker. At 430, the second circuit breaker receives the request from the first circuit breaker. At 440, the second circuit breaker interrupts the current flowing to the first circuit breaker. The second circuit breaker interrupts the current by temporarily turning off its semiconductor device, such as a SiC MOSFET or IGBT, through interrupt logic embedded in the upstream circuit breaker's memory. The interruption duration by the second circuit breaker can be adjusted for minimal impact on the downstream breaker's loads. The duration is measured in microseconds (µs). At 450, the first circuit breaker opens its mechanical contacts when the current flowing through it drops to a predetermined level. The second circuit breaker waits for a clear request signal from the first circuit breaker.The clear request signal may indicate that the mechanical contacts of the first circuit breaker have opened and it is therefore clear for the second circuit breaker to stop the interruption and resume normal operations. At 460, the first circuit breaker transmits the clear request to the second circuit breaker. In 470, the second circuit breaker stops interrupting current to the first circuit breaker based at least in part on the clear request received. The second circuit then resumes normal operation. Figure 5 is another flow diagram for a method 500 according to an exemplary embodiment of the present invention. The method can be implemented by an upstream circuit breaker and a downstream circuit breaker and the respective processing units coupled to the respective memories therein, as described with reference to Figures 1-3. In 510, both the downstream circuit breaker and the upstream circuit breaker are closed and performing normal operations. In 512, a fault event occurs within the downstream circuit breaker. The fault event may include an overcurrent event. In 514, the downstream circuit breaker detects that a failure mode has occurred. That is, the downstream circuit breaker detects that its solid-state switch has failed to open. In 516, the downstream circuit breaker transmits a request signal to the upstream circuit breaker. In 518, the upstream circuit breaker receives the request from the downstream circuit breaker. At 520, the upstream circuit breaker opens its solid-state switch to interrupt the current flowing to the downstream circuit breaker. In 522, the downstream circuit breaker detects the current level flowing through it, and when it detects that the current level has decreased to a predetermined level, the method proceeds to 526. The downstream circuit breaker can detect the zero crossing of the current through a current sensor (for example, a current sensor 400 discussed with reference to Figure 1). The predetermined level is a level at which it is safe for the downstream circuit breaker to open its mechanical contacts. At 524, the downstream circuit breaker opens its mechanical contacts. In 526, the downstream circuit breaker transmits the clear request to the upstream circuit breaker. At 528, the upstream circuit breaker receives the clear request from the downstream circuit breaker. In 530, the upstream circuit breaker stops interrupting the current flowing to the downstream circuit breaker by, for example, opening its solid-state switch. At 532, the upstream circuit breaker resumes normal operations. Although specific embodiments of the present invention have been described in detail, those skilled in the art will appreciate that various modifications and alternatives to these details could be developed in light of the general lessons of the disclosure. Accordingly, the particular provisions described are intended to be illustrative only and not limiting with respect to the scope of the present invention as defined in the appended claims.

Claims

1. A system comprising: a first circuit breaker (10; 10B-N) comprising a first solid-state switch (100), first mechanical contacts (500; 500A), and a current sensor (400) structured to detect current flowing through the first circuit breaker, the first mechanical contacts being coupled to the first solid-state switch in series along the path of the detected current; and a second circuit breaker (10A) electrically coupled to the first circuit breaker (10; 10B-N) and disposed upstream of the first circuit breaker, wherein the first circuit breaker (10;10B-N) is structured to transmit a request to the second circuit breaker (10A) upon detecting a fault mode, the fault mode comprising a failure to open the first solid-state switch (100) of the first circuit breaker, and wherein the second circuit breaker (10A) is structured to interrupt the current flowing to the first circuit breaker (10; 10B-N) in response to receiving the request, characterized in that: the first circuit breaker is further structured to open the first mechanical contacts (500; 500A) when the current flowing through the first circuit breaker decreases to a predetermined level; and the first circuit breaker (10; 10B-N) is further structured to transmit a clear request to the second circuit breaker (10A) when the first mechanical contacts (500;500A) have been opened, and the second circuit breaker is structured to stop interrupting the current flowing to the first circuit breaker in response to receiving a clear request from the first circuit breaker.

2. The system of claim 1, wherein the second circuit breaker (100A) includes a second solid-state switch (100), and wherein the second circuit breaker is structured to open the second solid-state switch (100) to interrupt the current flowing to the first circuit breaker (10; 10B-N) in response to receiving a request from the first circuit breaker; and wherein the second circuit breaker (10A) is structured to close the second solid-state switch (100) to stop interrupting the current flowing to the first circuit breaker (10; 10B-N) in response to receiving a clear request from the first circuit breaker (10;10B-N).

3. The system of claim 1, wherein the second circuit breaker (10A) includes second mechanical contacts (500A), and wherein the second circuit breaker is structured to open the second mechanical contacts to interrupt the current flowing to the first circuit breaker (10; 10B-N) in response to a request from the first circuit breaker, and wherein the second circuit breaker is structured to close the second mechanical contacts to cease interrupting the current flowing to the first circuit breaker in response to a clear request from the first circuit breaker.

4. The system of claim 1, wherein the predetermined current level comprises a current value that enables the first circuit breaker (10; 10B-N) to safely open the first mechanical contacts (500A;500A).

5. The system of claim 1, wherein the system further comprises a third circuit breaker (10N) disposed downstream of the second circuit breaker.

6. A method comprising: detecting a fault mode by means of a first circuit breaker (10; 10B-N), the fault mode comprising a failure to open a first solid-state switch (100) of the first circuit breaker, the first switch comprising the first solid-state circuit breaker, first mechanical contacts (500; 500A), and a current sensor (400) structured to detect current flowing through the first circuit breaker, the first mechanical contacts being coupled to the first solid-state switch in series in a path of the detected current; upon detecting a fault mode, transmitting, through the first circuit breaker (10;10B-N), a request to a second circuit breaker (10A), where the second circuit breaker (10A) is arranged upstream of the first circuit breaker (10; 10B-N); receiving the request by the second circuit breaker (10A); interrupting, with the second circuit breaker (10A), the current flowing to the first circuit breaker (10; 10B-N) in response to receiving the request; detecting that the current flowing through the first circuit breaker (10; 10B-N) has decreased to a predetermined level; opening, by the first circuit breaker (10; 10B-N), mechanical contacts (500; 500A) in response to the detection that the current flowing through the first circuit breaker has decreased to the predetermined level; transmit, through the first circuit breaker (10; 10B-N), a clear request to the second circuit breaker (10A) when the mechanical contacts (500; 500A) of the first circuit breaker (10;10B-N) have been opened; and stopping the interruption of the current flowing to the first circuit breaker (10; 10B-N) by the second circuit breaker (10A) in response to receiving the clear request.

7. The method of claim 6, wherein interrupting the current flowing to the first circuit breaker (10; 10B-N) comprises opening a second solid-state switch (100) of the second circuit breaker (10A), and wherein stopping the interruption of the current flowing through the first circuit breaker comprises closing the second solid-state switch of the second circuit breaker.

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