Solid state circuit interrupter with solid state interlock mechanism

Abstract

A system includes: a first circuit breaker (10B-10N) including a first solid-state switch (100), a first mechanical contact (500A), and a current sensor configured to sense current flowing through the first circuit breaker; and a second circuit breaker (10A) electrically coupled to the first circuit breaker (10B-10N) and configured to interrupt current flowing to the first circuit breaker, wherein the first circuit breaker (10B-10N) is configured to detect... When a fault mode of the first solid-state switch (100) is detected, a request (SSI request signal) is sent to the second circuit breaker (10A), wherein the second circuit breaker (10A) is configured to interrupt the current flowing to the first circuit breaker (10B-10N) in response to receiving the request, and the first circuit breaker (10B-10N) is further configured to disconnect the first mechanical contact (500A) when the current flowing through the first circuit breaker (10B-10N) drops to a predetermined level.

Description

Background Technology Technical Field

[0002] The concepts disclosed in this invention relate generally to circuit interrupters, and more particularly to circuit interrupters with solid-state interlocking mechanisms.

[0003] Background Information

[0004] Circuit interrupters (such as, but not limited to, circuit breakers) are typically used to protect circuits from overcurrent conditions, such as overload conditions, short circuits, or other fault conditions, such as arcing or grounding faults. Solid-state circuit interrupters use solid-state components, such as semiconductor devices, to connect and disconnect current flowing from a power source to a load. Solid-state circuit interrupters can offer advantages over conventional mechanical circuit interrupters, such as faster interruption, smaller size, or better reliability.

[0005] UL 489I is a survey requirements outline for solid-state molded case circuit breakers. It is used in conjunction with UL 489, which is a safety standard for molded case circuit breakers, molded case switches, and circuit breaker housings. UL 489I covers solid-state molded case circuit breakers with rated voltages up to 1000Vac and 1500Vdc that use semiconductors for switching and have an integral air gap for isolation. The semiconductor devices used are known to have leakage current, therefore an air gap is still required to provide current isolation for the load. Mechanical contact is typically used to create this air gap.

[0006] One advantage of solid-state circuit breakers over traditional circuit breakers lies in the size of their air gap. Solid-state circuit breakers can use much smaller air gaps and do not require arc slots because energy is dissipated within the semiconductor device itself. The reliability of the circuit breaker is based on the semiconductor's ability to interrupt current before the air gap is created.

[0007] However, one of the failure modes of solid-state components (e.g., semiconductor devices) is a short circuit. When such a short circuit occurs, the solid-state circuit breaker will fail to trip. This tripping failure of the circuit breaker can be detrimental to the solid-state circuit breaker, the circuit interruption system including the faulty solid-state circuit, and the load.

[0008] There is still room for improvement in solid-state circuit breakers and systems that include them. Summary of the Invention

[0009] These and other requirements are met through implementations of the disclosed concept, wherein a solid-state circuit breaker in fault mode requests an upstream circuit breaker to interrupt the current flowing to it, so that the solid-state circuit breaker can disconnect its mechanical contacts.

[0010] According to one aspect of the concept disclosed in the present invention, a system includes: a first circuit breaker including a first solid-state switch, a first mechanical contact, and a current sensor configured to sense current flowing through the first circuit breaker; and a second circuit breaker electrically coupled to the first circuit breaker and configured to interrupt current flowing to the first circuit breaker, wherein the first circuit breaker is configured to send a request to the second circuit breaker upon detecting a fault mode, and wherein the second circuit breaker is configured to interrupt current flowing to the first circuit breaker in response to receiving the request, and the first circuit breaker is further configured to disconnect the first mechanical contact when the current flowing through the first circuit breaker drops to a predetermined level.

[0011] According to another aspect of the concept disclosed in this invention, a solid-state circuit breaker includes: a solid-state switch configured to open to interrupt current flowing through the solid-state circuit breaker; a mechanical contact configured to open to provide current isolation; a current sensor configured to sense current flowing through the solid-state circuit breaker; and an electronic trip unit configured to control the solid-state switch to open or close and to control the mechanical contact to open, wherein the solid-state circuit breaker is configured to detect a fault mode of the solid-state switch and, in response, send a request to an upstream circuit breaker to interrupt current flowing to the solid-state circuit breaker.

[0012] According to another aspect of the concept disclosed in this invention, a method includes: detecting a fault mode by a first circuit breaker, the fault mode including a failure to disconnect a first solid-state switch of the first circuit breaker; sending a request from the first circuit breaker to a second circuit breaker; receiving the request by the second circuit breaker; interrupting current flowing to the first circuit breaker by the second circuit breaker in response to receiving the request; detecting that the current flowing through the first circuit breaker has dropped to a predetermined level; and disconnecting mechanical contacts by the first circuit breaker in response to detecting that the current flowing through the first circuit breaker has dropped to the predetermined level. Attached Figure Description

[0013] A complete understanding of the concepts disclosed in this invention can be obtained from the following description of preferred embodiments when read in conjunction with the accompanying drawings, wherein:

[0014] Figure 1 This is a schematic diagram of an exemplary embodiment of a solid-state circuit breaker according to the concepts disclosed in this invention;

[0015] Figure 2 This is another schematic diagram of a system according to an exemplary embodiment of the concepts disclosed in this invention;

[0016] Figure 3 The waveform of the current flowing through the circuit breaker is shown in an exemplary embodiment of the concept disclosed in the present invention;

[0017] Figure 4 This is a flowchart of a solid-state interlocking method according to an exemplary embodiment of the concept disclosed in this invention; and

[0018] Figure 5 This is another flowchart of a solid-state interlocking method according to an exemplary embodiment of the concept disclosed in the present invention. Detailed Implementation

[0019] Directional phrases used herein, such as, for example, left, right, front, back, top, bottom, and their derivatives, refer to the orientation of the elements shown in the accompanying drawings and do not limit the claims unless expressly stated herein.

[0020] As used in this article, the expression “connected” to two or more parts should be meant to mean that the parts are joined together directly or through one or more intermediate parts.

[0021] Figure 1 This is a schematic diagram of a solid-state circuit breaker 10 according to an exemplary embodiment of the concepts disclosed in this invention. The solid-state circuit breaker 10 may be part of a larger system, including additional circuit breakers, solid-state circuit breakers, and / or mechanical circuit breakers, such as… Figure 2 The system shown.

[0022] Solid-state circuit breaker 10 is configured to be electrically connected between the power source and the load 12 via line 2 and load conductor 4. An upstream circuit breaker may be installed between the power source and solid-state circuit breaker 10. Solid-state circuit breaker 10 is configured to trip or disconnect in the event of a fault condition (e.g., but not limited to an overcurrent condition) to interrupt the current flowing to the load 12, thereby protecting the load 12, the circuitry associated with the load 12, and the components within the solid-state circuit breaker 10.

[0023] 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. Solid-state switch 100 includes solid-state switching elements (e.g., but not limited to metal-oxide-semiconductor field-effect transistors (MOSFETs) and insulated-gate bipolar transistors (IGBTs)) configured to turn on and off (i.e., open and close) to allow or interrupt current flow to load 12. Solid-state switch 100 is electrically coupled to load 12 and electronic trip unit 200.

[0024] The electronic trip unit 200 is configured to control the solid-state switch 100 to open and close based on signals from sensor 400, and also controls the operating mechanism 300 to trip and disconnect mechanical contact 500. The electronic trip unit 200 may include a processing unit, which may include a processor and memory. The processor may be, for example, but not limited to, a microprocessor, a microcontroller, or some other suitable processing device or circuit. The memory may be any one or more of various types of internal and / or external storage media, such as, but not limited to, RAM, ROM, EPROM, EEPROM, FLASH, etc., which provide storage registers (i.e., machine-readable media) for data storage, such as data storage in the manner of a computer's internal storage area, and may be volatile or non-volatile memory. The memory may store firmware solutions for solid-state interlocking (SSI), where a first solid-state circuit breaker (e.g., a downstream circuit breaker) is unable to disconnect its solid-state switch, for example, due to a short circuit in the solid-state switch therein. SSI is performed by a first solid-state circuit breaker and a second circuit breaker, for example, to an upstream circuit breaker of the first solid-state circuit breaker. The second circuit breaker may or may not be a solid-state circuit breaker. Downstream circuit breaker circuits supporting SSI and upstream circuit breakers supporting SSI can jointly monitor and respond to the interruption capability of their power semiconductors. (Reference) Figure 2 Further discussion on SSI.

[0025] The electronic trip unit 200 is configured to determine a fault condition (e.g., but not limited to an overcurrent fault) and control the solid-state switch 100 to trip in response to the fault condition. Tripping the solid-state switch 100 interrupts the current flowing to the load 12.

[0026] Operating mechanism 300 is configured to disconnect mechanical contact 500 in response to a signal from electronic trip unit 200. Disconnecting mechanical contact 500 provides current isolation between the power supply and load 12. For example, and without limitation, operating mechanism 300 is configured to disconnect mechanical contact 500 by, for example, but not limited to, moving a movable arm, to separate mechanical contact 500. Electronic trip unit 200 is configured to control operating mechanism 300 to disconnect mechanical contact 500 only after solid-state switch 100 has been opened to interrupt current flowing through solid-state circuit breaker 10. In some exemplary embodiments, mechanical contact 500 is not designed to interrupt rated current flowing through solid-state circuit breaker 10, and solid-state circuit breaker 10 may not contain components such as arc chute to handle the effect of mechanical contact 500 interrupting rated current. Therefore, mechanical contact 500 should only disconnect when the current flowing through solid-state circuit breaker 10 has dropped to a level that would safely disconnect mechanical contact 500.

[0027] Sensor 400 may be a current sensor (e.g., but not limited to, a current transformer, a Hall effect sensor, etc.) configured to sense the current flowing through the solid-state circuit breaker 10. The output of sensor 400 may be provided to electronic trip unit 200.

[0028] Electronic trip unit 200 is configured to detect a fault mode of solid-state circuit breaker 10. The fault mode is a failure where solid-state switch 100 is open. In response to detecting a fault mode, electronic trip unit 200 is configured to output a request to an upstream circuit breaker. In response to this request, the upstream circuit breaker is configured to interrupt the current flowing to solid-state circuit breaker 10, thereby causing a decrease in the current flowing through solid-state circuit breaker 10. Electronic trip unit 200 is configured to monitor the current flowing through solid-state circuit breaker 10 and, when the current decreases, determine when the current drops to a predetermined level. This predetermined level is the level at which mechanical contact 500 is safely disconnected. An exemplary predetermined level is 5A. However, the predetermined level can be modified without departing from the scope of the disclosed concept. Once the current reaches the predetermined level, electronic trip unit 200 controls operating mechanism 300 to disconnect mechanical contact 500. After disconnecting mechanical contact 500, electronic trip unit 200 sends an explicit request to the upstream circuit breaker. This explicit request instructs the upstream circuit breaker to stop interrupting the current flowing to solid-state circuit breaker 10. The reduction in current flowing through solid-state circuit breaker 10 allows for the safe disconnection of mechanical contacts 500. This explicit request allows the upstream circuit breaker to quickly restore current, minimizing disruption to other loads downstream of that upstream circuit breaker. In some exemplary embodiments, the duration of the interruption can be on the order of microseconds, with minimal impact on other loads downstream of the upstream circuit breaker.

[0029] Figure 2 This is a schematic diagram of a system 1 according to an exemplary embodiment of the concepts disclosed in this invention. System 1 may include one or more solid-state circuit breakers 10. Figure 2 In this system, system 1 includes multiple circuit breakers, such as upstream circuit breaker 10A and downstream solid-state circuit breakers 10B-10N, where N is an integer. Upstream circuit breaker 10A may or may not be a solid-state circuit breaker.

[0030] Circuit breakers 10A-10N are electrically coupled to each other and communicate with each other via any suitable communication protocol. For example, circuit breakers 10A-10N can be configured to communicate via wired or wireless communication. In wired communication, circuit breakers 10A-10N can communicate via power lines or via control lines. It should be understood that any suitable communication method can be used between circuit breakers 10A-10N without departing from the scope of the concepts disclosed in this invention. When a fault mode is detected (e.g., failure to disconnect a solid-state switch) and one or more solid-state circuit breakers fail to disconnect, circuit breakers 10A-10N can communicate with each other to, for example, request or execute a solid-state interlock (SSI). For example, if the solid-state switch 100 of downstream solid-state circuit breaker 10B is short-circuited by 100A, the solid-state switch 100 of downstream solid-state circuit breaker 10B may fail to disconnect. When solid-state switch 100 fails to disconnect and current continues to flow through downstream solid-state circuit breaker 10B, disconnecting mechanical contact 500A is unsafe. In response to a fault mode, the downstream circuit breaker 10B sends a request (e.g., an SSI request) to the upstream circuit breaker 10A.

[0031] SSI (Short-Circuit Switch Initiation) is a hardware and firmware solution for one of the fault modes associated with the power semiconductor devices in a solid-state circuit breaker. SSI provides firmware solutions, such as communication schemes, and allows upstream circuit breakers to identify and respond to downstream circuit breakers in fault modes when the solid-state circuit breaker fails to trip during a short-circuit event. For example, when an SSI-enabled solid-state circuit breaker senses a short-circuit fault in one or more of its semiconductor devices, it sends an SSI request to the nearest upstream circuit breaker, and in response, the nearest upstream circuit breaker interrupts the current flowing to the downstream circuit breaker. An SSI request could indicate that the solid-state switch of downstream circuit breaker 10B is faulty and request upstream circuit breaker 10A to interrupt the current flowing to downstream circuit breaker 10B. SSI can be performed using interrupt logic embedded in the circuit breaker.

[0032] Downstream circuit breaker 10B is configured to monitor the current drop due to an interruption and then disconnect its mechanical contacts 500A when the current reaches a predetermined level. This predetermined level can be the current level at which the mechanical contacts of the circuit breaker are required to safely disconnect at all stages. Upstream circuit breaker 10A can generate an interrupt current flowing to downstream circuit breaker 10B by temporarily shutting down its semiconductor devices (e.g., SiC MOSFETs, IGBTs, 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 duration of zero current can be in the microsecond range (μs). In examples where the upstream circuit breaker is a non-solid-state circuit breaker (non-SSCB), the non-SSCB upstream circuit breaker can interrupt the current by disconnecting its mechanical contacts. Therefore, a non-SSCB may also require additional action to reclose itself. However, in some exemplary embodiments, a non-SSCB may be able to reclose its mechanical contacts.

[0033] Once the current is interrupted, the downstream solid-state circuit breaker 10B activates via a current sensor (e.g., reference current sensor). Figure 1 The current sensor 400 detects whether the drop in current flowing through it has reached a predetermined level and disconnects its mechanical contact 500A. Upon disconnecting mechanical contact 500A, the downstream circuit breaker 10B can send an explicit request to the upstream circuit breaker 10A. This explicit request can indicate that the fault mode has been repaired; for example, the mechanical contact of the downstream circuit breaker 10B has now been disconnected, and therefore it is explicit that the upstream circuit breaker 10A needs to terminate the SSI mechanism and restore its normal operation.

[0034] Upon receiving an explicit request, the upstream circuit breaker 10A can terminate the SSI, for example, by closing its mechanical contacts or solid-state switches. The upstream circuit breaker 10A then resumes its normal operation.

[0035] Figure 3 The waveforms of the current flowing through the downstream and upstream circuit breakers are included in exemplary embodiments of the concepts disclosed in this invention. A is the waveform of the current flowing through the downstream circuit breaker (e.g., a downstream solid-state circuit breaker supporting SSI). B is the waveform of the current flowing through the upstream circuit breaker (e.g., an upstream circuit breaker supporting SSI).

[0036] At time t1, both the downstream circuit breaker and the upstream circuit breaker are closed.

[0037] A fault mode (i.e., failure to disconnect the solid-state switch) occurs in the downstream circuit breaker after time t1 and before time t2. The downstream circuit breaker detects this fault mode.

[0038] At time t2, the downstream circuit breaker sends 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 flowing through it to drop to a predetermined level that would allow it to safely disconnect its mechanical contacts.

[0039] At time t3, the current flowing through the downstream circuit breaker reaches a predetermined level. In one example, for a 100A solid-state circuit breaker, the predetermined level could be 5A or less. However, it should be understood that other predetermined levels may be used without departing from the scope of the concepts disclosed in this invention. At time t3, the downstream circuit breaker can begin the process of disconnecting its mechanical contacts. Since this process requires a certain amount of time, the mechanical contacts may actually not be disconnected until t4. Once the mechanical contacts are disconnected, the downstream circuit breaker sends an explicit request to the upstream circuit breaker, instructing the upstream circuit breaker to cease interrupting the current flowing to the downstream circuit breaker.

[0040] At time t5, the upstream circuit breaker can receive an explicit request from the downstream circuit breaker and stop the interruption of current flowing to the downstream circuit breaker by, for example, closing its solid-state switch or mechanical contact.

[0041] 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 is reached at time t6.

[0042] Figure 4 This is a flowchart of an exemplary embodiment of a method 400 according to the concepts disclosed in this invention. The method can be derived from reference... Figures 1 to 3 The upstream and downstream circuit breakers of the circuit interrupter, as well as the corresponding processing units, are executed.

[0043] At point 410, the first circuit breaker detected a fault mode (i.e., failure to open the solid-state switch). This first circuit breaker can be as described in the reference... Figure 2 The downstream circuit breaker mentioned above.

[0044] The request can indicate a fault in the solid-state switch 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 sends the request to the second circuit breaker. The second circuit breaker can be as shown in the reference. Figure 2 The upstream circuit breaker. One or more upstream circuit breakers may be present within the circuit interrupter, and the downstream circuit breaker sends an SSI request signal to the nearest upstream circuit breaker. The upstream circuit breaker can be a solid-state circuit breaker or a non-solid-state circuit breaker.

[0045] At 430, the second circuit breaker receives a request from the first circuit breaker.

[0046] At position 440, the second circuit breaker interrupts the current flowing to the first circuit breaker. The second circuit breaker can interrupt the current by temporarily shutting down its semiconductor devices, such as SiC MOSFETs and IGBTs, via interrupt logic embedded in the memory of the upstream circuit breaker. The duration of the interruption by the second circuit breaker can be adjusted to minimize the impact on the load of the downstream circuit breaker. This duration is in the microsecond range (μs).

[0047] At 450, when the current flowing through the first circuit breaker drops to a predetermined level, the first circuit breaker disconnects its mechanical contacts. The second circuit breaker awaits an explicit request signal from the first circuit breaker. This explicit request signal indicates that the mechanical contacts of the first circuit breaker have been disconnected, and therefore, explicitly requires the second circuit breaker to stop the interruption and resume its normal operation.

[0048] At point 460, the first circuit breaker sends an explicit request to the second circuit breaker.

[0049] At point 470, the second circuit breaker, at least in part, stops interrupting the current flowing to the first circuit breaker based on the received explicit request. The second circuit breaker then resumes normal operation.

[0050] Figure 5 This is another flowchart of a method 500 according to an exemplary embodiment of the concepts disclosed in the present invention. The method can be derived from reference... Figures 1 to 3 The upstream and downstream circuit breakers of the circuit interrupter, as well as the corresponding processing units of the corresponding memory coupled thereto, are executed.

[0051] At point 510, both the downstream and upstream circuit breakers closed and performed normal operation.

[0052] At point 512, a fault event occurs in the downstream circuit breaker. This fault event may include an overcurrent event.

[0053] At point 514, the downstream circuit breaker detected a fault mode. In other words, the downstream circuit breaker detected that its solid-state switch could not disconnect.

[0054] At point 516, the downstream circuit breaker sends a request signal to the upstream circuit breaker.

[0055] At point 518, the upstream circuit breaker receives a request from the downstream circuit breaker.

[0056] At point 520, the upstream circuit breaker disconnects its solid-state switch to interrupt the current flowing to the downstream circuit breaker.

[0057] At 522, the downstream circuit breaker detects the current level flowing through it, and when it detects that the current level has dropped to a predetermined level, the method proceeds to 526. The downstream circuit breaker can be connected via a current sensor (e.g., reference...). Figure 1The current sensor 400 under discussion detects zero current. This predetermined level is the level at which the downstream circuit breaker safely disconnects its mechanical contacts.

[0058] At point 524, the downstream circuit breaker disconnects its mechanical contacts.

[0059] At point 526, the downstream circuit breaker sends an explicit request to the upstream circuit breaker.

[0060] At point 528, the upstream circuit breaker receives the explicit request from the downstream circuit breaker.

[0061] At 530, the upstream circuit breaker stops interrupting the current flowing to the downstream circuit breaker by, for example, disconnecting its solid-state switch.

[0062] At point 532, the upstream circuit breaker resumed normal operation.

[0063] While specific embodiments of the concepts disclosed in this invention have been described in detail, those skilled in the art will understand that various modifications and substitutions to those details can be developed based on the overall teachings of this disclosure. Therefore, the specific arrangements disclosed are merely illustrative and do not limit the scope of the concepts disclosed in this invention, which is defined by the full scope of the appended claims and any and all their equivalents.

Claims

1. A circuit interruption system, comprising: A first circuit breaker, the first circuit breaker including a first solid-state switch, a first mechanical contact and a current sensor, the current sensor being configured to sense the current flowing through the first circuit breaker; and A second circuit breaker, electrically coupled to the first circuit breaker and configured to interrupt current flowing to the first circuit breaker. The first circuit breaker is configured to send a request to the second circuit breaker when a fault mode is detected, and The second circuit breaker is configured to interrupt current flowing to the first circuit breaker in response to receiving the request, and the first circuit breaker is further configured to disconnect the first mechanical contact when the current flowing through the first circuit breaker drops to a predetermined level, wherein the second circuit breaker includes a second solid-state switch, and wherein the second circuit breaker is configured to disconnect the second solid-state switch to interrupt current flowing to the first circuit breaker in response to receiving the request from the first circuit breaker. The first circuit breaker is further configured to send an explicit request to the second circuit breaker when the first mechanical contact has been broken, and the second circuit breaker is configured to close the second solid-state switch to stop interrupting the current flowing to the first circuit breaker in response to receiving the explicit request from the first circuit breaker.

2. The system of claim 1, wherein the second circuit breaker includes a second mechanical contact, and wherein the second circuit breaker is configured to, in response to receiving the request from the first circuit breaker, open the second mechanical contact to interrupt current flowing to the first circuit breaker, and wherein the first circuit breaker is further configured to, when the first mechanical contact has been opened, send an explicit request to the second circuit breaker, and wherein the second circuit breaker is configured to, in response to receiving the explicit request from the first circuit breaker, close the second mechanical contact to stop interrupting current flowing to the first circuit breaker.

3. The system of claim 1, wherein the predetermined current level includes a current value that allows the first circuit breaker to safely disconnect the first mechanical contact.

4. The system of claim 1, wherein the second circuit breaker is configured to stop interrupting the current flowing to the first circuit breaker for a predetermined time after interrupting the current flowing to the first circuit breaker.

5. The system of claim 1, wherein the second circuit breaker is disposed upstream of the first circuit breaker, and wherein the system further comprises a third circuit breaker disposed downstream of the second circuit breaker.

6. The system of claim 1, wherein the failure mode includes failure to disconnect the first solid-state switch.

7. A solid-state circuit breaker, comprising: A solid-state switch, the solid-state switch being configured to open to interrupt the current flowing through the solid-state circuit breaker; Mechanical contact, which is configured to be disconnected to provide electrical isolation; A current sensor configured to sense the current flowing through the solid-state circuit breaker; and An electronic trip unit is configured to control the solid-state switch to open or close and to control the mechanical contacts to disconnect. The solid-state circuit breaker is configured to detect fault modes of the solid-state switch and, in response, send a request to an upstream circuit breaker to interrupt the current flowing to the solid-state circuit breaker. The solid-state circuit breaker is further configured to send an explicit request to the upstream circuit breaker to stop interrupting the current flowing to the solid-state circuit breaker when the mechanical contact has been broken.

8. The solid-state circuit breaker of claim 7, wherein the electronic trip unit is configured to detect whether the current flowing through the solid-state circuit breaker drops to a predetermined level, and to control the mechanical contacts to disconnect when the current flowing through the solid-state circuit breaker drops to the predetermined level.

9. The solid-state circuit breaker of claim 8, wherein the electronic trip unit is configured to send an explicit request to the upstream circuit breaker after controlling the mechanical contact to disconnect, and wherein the predetermined level includes a current value that allows the solid-state circuit breaker to safely disconnect the mechanical contact.

10. A circuit interruption method, comprising: The fault mode is detected by the first circuit breaker, and the fault mode includes failure to disconnect the first solid-state switch of the first circuit breaker; The first circuit breaker sends a request to the second circuit breaker; The request is received by the second circuit breaker; In response to receiving the request, the second circuit breaker interrupts the current flowing to the first circuit breaker; The current flowing through the first circuit breaker has been detected to have dropped to a predetermined level; In response to the detection that the current flowing through the first circuit breaker has dropped to the predetermined level, the mechanical contacts are disconnected by the first circuit breaker; When the mechanical contact has been broken, the first circuit breaker sends an explicit request to the second circuit breaker; as well as In response to receiving the explicit request, the second circuit breaker stops interrupting the current flowing to the first circuit breaker.

11. The method of claim 10, wherein interrupting the current flowing to the first circuit breaker comprises opening the second solid-state switch of the second circuit breaker, and wherein stopping the interruption of the current flowing to the first circuit breaker comprises closing the second solid-state switch of the second circuit breaker.

12. The method of claim 10, further comprising: The interruption of the current flowing to the first circuit breaker is stopped within a predetermined time after the interruption of the current flowing to the first circuit breaker.

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