Multistage power distribution protection method and device

Abstract

The invention discloses a multi-stage power distribution protection method. According to the method, a multi-stage circuit breaker system is used for power distribution protection, lower-stage circuit breakers have a current transformer disconnection detection function, and upper-stage circuit breakers and the lower-stage circuit breakers are in communication connection; each subordinate circuit breaker transmits the current detection value of each phase of the subordinate circuit breaker and the disconnection detection information of the current transformer to the superior circuit breaker in real time; when the upper-level circuit breaker receives the information, which is sent by the lower-level circuit breaker, of the occurrence of the disconnection fault of the current transformer, the upper-level circuit breaker estimates the current of the fault circuit breaker according to the current detection value of the upper-level circuit breaker and the current detection values of the other normal lower-level circuit breakers, and transmits the obtained current estimation value to the fault circuit breaker; and the fault circuit breaker performs current protection by taking the current estimation value as a current detection value of the fault circuit breaker. The invention further discloses a multi-stage power distribution protection device. According to the invention, the current protection failure problem and the override trip risk during the disconnection fault of the current transformer can be effectively prevented.

Description

Technical Field

[0001] This invention relates to a power distribution protection method, and more particularly to a multi-level power distribution protection method. Background Technology

[0002] Circuit breakers, which measure current and provide current protection via current transformers, are core components for power grid distribution protection. A current transformer open circuit failure will cause the circuit breaker's current protection function to malfunction. To improve the safety and reliability of circuit breakers, researchers have proposed a series of current transformer open circuit detection technologies for automatic detection of such faults, such as the single-ended current discrimination method (see the literature "Current Transformer Open Circuit Detection Based on Single-Ended Current") and the injection signal-based detection method (see Chinese Patent CN109991563B).

[0003] However, existing technology responds to the detection of a current transformer open circuit fault in a circuit breaker by issuing an alarm signal to notify the user. If the user fails to respond promptly, there is a risk that a current fault may occur in the circuit without the circuit breaker providing current protection. In multi-stage power distribution protection schemes using multi-stage circuit breaker systems, this situation may cause the upstream circuit breaker to perform a protection action, i.e., cascading tripping, leading to an expanded power outage area, damage to electrical equipment, impact on power system stability, increased maintenance costs, and longer power restoration time. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a multi-level power distribution protection method, which can effectively prevent the current protection failure problem when the current transformer of the downstream circuit breaker is disconnected and the risk of possible over-level tripping.

[0005] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems: A multi-level power distribution protection method utilizes a multi-level circuit breaker system for power distribution protection. Each downstream circuit breaker in the system possesses a current transformer disconnection detection function, and each downstream circuit breaker communicates with its upstream circuit breaker. Each downstream circuit breaker transmits its own phase current detection values ​​and current transformer disconnection detection information to the upstream circuit breaker in real time. When the upstream circuit breaker receives information from its downstream circuit breaker indicating a current transformer disconnection fault, it estimates the current of the downstream circuit breaker with the fault by subtracting the sum of the current detection values ​​of the other normal downstream circuit breakers from its own current detection value. The upstream circuit breaker then transmits the estimated current value to the downstream circuit breaker with the fault, which uses this estimated current value as its own current detection value for current protection.

[0006] Furthermore, when a downstream circuit breaker detects a current transformer disconnection fault within itself, it sets the current detection value of the corresponding phase with the current transformer disconnection fault to zero and then transmits it to the upstream circuit breaker.

[0007] Based on the same inventive concept, the following technical solutions can also be obtained: A multi-level power distribution protection device uses a multi-level circuit breaker system for power distribution protection. Each lower-level circuit breaker in the multi-level circuit breaker system has a current transformer disconnection detection function, and each lower-level circuit breaker is communicatively connected to its upper-level circuit breaker. Each lower-level circuit breaker transmits its own phase current detection value and current transformer disconnection detection information to the upper-level circuit breaker in real time. When the upper-level circuit breaker receives the current transformer disconnection fault information sent by its lower-level circuit breaker, the upper-level circuit breaker estimates the current of the lower-level circuit breaker with the current transformer disconnection fault by subtracting the sum of the current detection values ​​of the other normal lower-level circuit breakers from its own current detection value, and transmits the obtained current estimation value to the lower-level circuit breaker with the current transformer disconnection fault. The lower-level circuit breaker with the current transformer disconnection fault uses the current estimation value as its own current detection value for current protection.

[0008] Furthermore, when a downstream circuit breaker detects a current transformer disconnection fault within itself, it sets the current detection value of the corresponding phase with the current transformer disconnection fault to zero and then transmits it to the upstream circuit breaker.

[0009] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: This invention is based on the communication function of a multi-level circuit breaker system. When the current detection function of a downstream circuit breaker fails due to a current transformer disconnection fault, the upstream circuit breaker estimates the current of the faulty downstream circuit breaker based on its own current detection value and the current detection values ​​of other normal downstream circuit breakers. The faulty downstream circuit breaker then performs corresponding current protection based on the estimated current value, thereby effectively restoring the current protection function of the downstream circuit breaker and avoiding cascading tripping and a series of problems caused by it. Attached Figure Description

[0010] Figure 1 A topology diagram for a specific example of a multi-stage circuit breaker system; Figure 2 A software flowchart for a specific example of a multi-stage circuit breaker system; Figure 3 This is a process diagram in a specific embodiment; Figure 4 This is a flowchart illustrating the communication process in a specific embodiment. Detailed Implementation

[0011] To address the problem of circuit breaker current detection function failure caused by current transformer open circuit faults, the present invention addresses this issue by leveraging the communication function of a multi-stage circuit breaker system. When a downstream circuit breaker's current detection function fails due to a current transformer open circuit fault, the upstream circuit breaker estimates the current of the faulty downstream circuit breaker based on its own current detection value and the current detection values ​​of other normal downstream circuit breakers. The faulty downstream circuit breaker then performs corresponding current protection based on this estimated current value, effectively restoring the current protection function of the downstream circuit breaker and preventing cascading tripping and related problems.

[0012] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems: A multi-level power distribution protection method utilizes a multi-level circuit breaker system for power distribution protection. Each downstream circuit breaker in the system possesses a current transformer disconnection detection function, and each downstream circuit breaker communicates with its upstream circuit breaker. Each downstream circuit breaker transmits its own phase current detection values ​​and current transformer disconnection detection information to the upstream circuit breaker in real time. When the upstream circuit breaker receives information from its downstream circuit breaker indicating a current transformer disconnection fault, it estimates the current of the downstream circuit breaker with the fault by subtracting the sum of the current detection values ​​of the other normal downstream circuit breakers from its own current detection value. The upstream circuit breaker then transmits the estimated current value to the downstream circuit breaker with the fault, which uses this estimated current value as its own current detection value for current protection.

[0013] A multi-level power distribution protection device uses a multi-level circuit breaker system for power distribution protection. Each lower-level circuit breaker in the multi-level circuit breaker system has a current transformer disconnection detection function, and each lower-level circuit breaker is communicatively connected to its upper-level circuit breaker. Each lower-level circuit breaker transmits its own phase current detection value and current transformer disconnection detection information to the upper-level circuit breaker in real time. When the upper-level circuit breaker receives the current transformer disconnection fault information sent by its lower-level circuit breaker, the upper-level circuit breaker estimates the current of the lower-level circuit breaker with the current transformer disconnection fault by subtracting the sum of the current detection values ​​of the other normal lower-level circuit breakers from its own current detection value, and transmits the obtained current estimation value to the lower-level circuit breaker with the current transformer disconnection fault. The lower-level circuit breaker with the current transformer disconnection fault uses the current estimation value as its own current detection value for current protection.

[0014] Each downstream circuit breaker can communicate with its upstream circuit breaker using various existing wireless or wired communication methods, such as fieldbus, industrial Ethernet, WIFI, power line carrier, etc.

[0015] To facilitate public understanding, the technical solution of the present invention will be described in detail below through specific embodiments and in conjunction with the accompanying drawings: The multi-level power distribution protection device in this embodiment uses, as follows: Figure 1 The two-level circuit breaker system shown provides power distribution protection. This two-level circuit breaker system consists of an upstream circuit breaker and a group of downstream circuit breakers. The circuit breakers are connected to each other via a fieldbus. Each downstream circuit breaker has a current transformer disconnection detection function, which can detect its own current transformer disconnection fault.

[0016] When a current transformer disconnection fault occurs in a downstream circuit breaker, the current detection and current protection functions will fail. Current technology only uses the method of issuing an alarm signal to notify the user to handle the situation. The current protection function of the downstream circuit breaker with the current transformer disconnection fault cannot be restored, and it may cause the upstream circuit breaker to trip out of turn.

[0017] According to Kirchhoff's Current Law, in parallel or radial power distribution networks, the total current equals the sum of the currents in each branch. Based on this principle, when a downstream circuit breaker fails to detect current due to a current transformer disconnection, the current of the faulty downstream circuit breaker can be estimated using the current detection values ​​of the upstream circuit breaker and the current detection values ​​of the other normal downstream circuit breakers. This allows the current detection and current protection functions of the faulty circuit breaker to be restored. The circuit breaker software flowchart is shown below. Figure 2 As shown.

[0018] In this embodiment, the system performs sampling and time synchronization. The upstream circuit breaker sends a sampling and time synchronization signal at regular intervals. After sending the sampling and time synchronization signal and delaying the data transmission time, the upstream circuit breaker restarts sampling the current signal. The downstream circuit breaker restarts sampling the current signal after receiving the sampling and time synchronization signal, thus synchronizing the current values ​​calculated by the upstream and downstream circuit breakers.

[0019] Taking a three-phase circuit breaker as an example, each downstream circuit breaker transmits its own phase current detection values ​​and current transformer disconnection detection information to the upstream circuit breaker in real time via fieldbus. Specifically, the downstream circuit breaker 1 sends the following content: 1, I1A, I1B, I1C, DX1A, DX1B, DX1C, where 1 is the circuit breaker's communication address; I1A is the A-phase current of the downstream circuit breaker 1, I1B is the B-phase current of the downstream circuit breaker 1, and I1C is the C-phase current of the downstream circuit breaker 1; DX1A is the A-phase current transformer disconnection information of the downstream circuit breaker 1, DX1B is the B-phase current transformer disconnection information of the downstream circuit breaker 1, and DX1C is the C-phase current transformer disconnection information of the downstream circuit breaker 1. The values ​​of DX1A, DX1B, and DX1C are 0 or 1, where 0 indicates no disconnection and 1 indicates disconnection. ... The downstream circuit breaker n sends the following content: n, InA, InB, InC, DXnA, DXnB, and DXnC, where n is the communication address of the circuit breaker; InA is the A-phase current of the downstream circuit breaker n, InB is the B-phase current of the downstream circuit breaker n, and InC is the C-phase current of the downstream circuit breaker n; DXnA is the disconnection information of the A-phase current transformer of the downstream circuit breaker n, DXnB is the disconnection information of the B-phase current transformer of the downstream circuit breaker n, and DXnC is the disconnection information of the C-phase current transformer of the downstream circuit breaker n. The values ​​of DXnA, DXnB, and DXnC are 0 or 1, where 0 indicates no disconnection and 1 indicates disconnection. The upstream circuit breaker receives the phase current values ​​and current transformer disconnection information of the downstream circuit breaker via the fieldbus. Assuming that the A-phase current transformer of the downstream circuit breaker 1 is disconnected, to prevent the measured current from being non-zero due to external electromagnetic interference after the transformer disconnection, it is preferable to set the current of this phase to 0. The downstream circuit breaker 1 sets I1A to 0 and DX1A to 1 and then transmits the relevant information to the upstream circuit breaker via the bus. When the upstream circuit breaker receives DX1A as 1, it calculates the estimated value of the A-phase current of the downstream circuit breaker 1: I1A'=IA - I1A ......- InA; where I1A' is the estimated value of the A-phase current of the downstream circuit breaker 1, IA is the detected value of the A-phase current of the upstream circuit breaker, I1A is the detected value of the A-phase current of the downstream circuit breaker 1, and InA is the detected value of the A-phase current of the downstream circuit breaker n. The calculated estimated value of the A-phase current of the downstream circuit breaker 1, I1A', is then transmitted to the downstream circuit breaker 1 via the bus communication. The downstream circuit breaker 1 uses the received I1A' as its own current detection value to perform overload, short-circuit short-delay, and short-circuit instantaneous current protection, thereby restoring the current protection function. Among them, the instantaneous protection can be achieved by increasing the delay to avoid the influence of non-periodic components.

[0020] like Figure 3 , Figure 4 As shown, the above embodiment is further described in detail. Taking a system with one upstream circuit breaker and three downstream circuit breakers as an example, the system uses a CAN fieldbus connection. The data transmission time is about 0.1ms. The circuit breaker collects the signal (AD value) output by the current transformer and signal conditioning circuit every 0.3125ms and saves the AD value into the AD buffer (64 points, 20ms). Every 10ms, the AD buffer calculates the current effective value. The upstream circuit breaker sends a sampling time synchronization signal (0, 'D', 'S') every minute. After sending the sampling time synchronization signal and delaying for 0.1ms, the upstream circuit breaker sets its AD buffer pointer to 0 and restarts its AD sampling timer. Upon receiving the sampling time synchronization signal (0, 'D', 'S'), the downstream circuit breaker sets its corresponding AD buffer pointer to 0 and restarts its corresponding AD sampling timer. The calculated effective current values ​​of the upstream and downstream circuit breakers after 20ms are synchronized effective current values.

[0021] The effective current values ​​calculated by the upstream circuit breaker are IA, IB, and IC; the effective current values ​​calculated by circuit breaker 1 are I1A, I1B, and I1C; the effective current values ​​calculated by circuit breaker 2 are I2A, I2B, and I2C; and the effective current values ​​calculated by circuit breaker 3 are I3A, I3B, and I3C. After calculating the effective value of the current, the downstream circuit breaker performs current transformer disconnection detection (e.g., using a detection method based on injected signals), and obtains: The current transformer disconnection information for circuit breaker 1 is DX1A, DX1B, and DX1C. The current transformer disconnection information for circuit breaker 2 is DX2A, DX2B, and DX2C. The current transformer disconnection information for circuit breaker 3 is DX3A, DX3B, and DX3C. The values ​​of DX1A, DX1B, DX1C...DX3A, DX3B, DX3C are 0 to indicate no disconnection and 1 to indicate no disconnection.

[0022] When a current transformer is detected to be disconnected, the corresponding current value is set to 0.

[0023] The downstream circuit breaker sends data after calculating the effective value of the current: The downstream circuit breaker 1 sends the following information: 1, I1A, I1B, I1C, DX1A, DX1B, DX1C; The downstream circuit breaker 2 sends the following information: 2, I2A, I2B, I2C, DX2A, DX2B, DX2C; The downstream circuit breaker 3 sends the following information: 3, I3A, I3B, I3C, DX3A, DX3B, DX3C. After receiving the data sent by the lower circuit breakers 1, 2, and 3, the upper circuit breaker calculates the estimated value of the phase current corresponding to the disconnected circuit breaker. For example, if the current transformer of phase A of lower circuit breaker 1 is disconnected, the upper circuit breaker can receive data 1, 0, I1B, I1C, 1, 0, 0. The upper circuit breaker determines that the communication address 1, DX1A is 1, and calculates the estimated value of phase A current of lower circuit breaker 1: I1A'=IA - 0 - I2A - I3A.

[0024] The upstream circuit breaker sends data to the CAN bus: 1, 'A', I1A', where 1 is the communication address of the disconnected circuit breaker and 'A' is the disconnected phase.

[0025] After receiving the data, the downstream circuit breaker 1 replaces I1A with I1A' to perform overload, short-circuit short-delay, and short-circuit instantaneous protection.

[0026] The specific process of patent implementation is as follows: The upstream circuit breaker Ir2 = 400A, t2 = 0.2s; the downstream circuit breaker Ir2 = 100A, t2 = 0.1s; where Ir2 is the short-circuit short-delay current; t2 is the short-circuit short-delay time.

[0027] Time T0: System is normal; sampling and time synchronization operation is performed. (T0+20ms) time: Upstream circuit breaker: IA=240A, IB=240A, IC=240A; Downstream circuit breaker 1: I1A=80A, I1B=80A, I1C=80A, DX1A=0, DX1B=0, DX1C=0; Downstream circuit breaker 2: I2A=80A, I2B=80A, I2C=80A, DX2A=0, DX2B=0, DX2C=0; Downstream circuit breaker 3: I3A=80A, I3B=80A, I3C=80A, DX3A=0, DX3B=0, DX3C=0; At time T1: A current fault occurs in phase A of the downstream circuit breaker 1, and the current transformer in phase A is disconnected at the same time. (T1+10ms) Time: (Calculate the effective value of current and disconnection information every 10ms) Upstream circuit breaker: IA=440A, IB=240A, IC=240A; Downstream circuit breaker 1: I1A=0, I1B=80A, I1C=80A, DX1A=1, DX1B=0, DX1C=0; Downstream circuit breaker 2: I2A=80A, I2B=80A, I2C=80A, DX2A=0, DX2B=0, DX2C=0; Downstream circuit breaker 3: I3A=80A, I3B=80A, I3C=80A, DX3A=0, DX3B=0, DX3C=0; The downstream circuit breaker 1 sends data 1, 0, 80, 80, 1, 0, 0; Downstream circuit breaker 2: Send data 2, 80, 80, 80, 0, 0, 0; Downstream circuit breaker 3: Sends data 3, 80, 80, 80, 0, 0, 0; When IA is greater than Ir2 (400A) of the upstream circuit breaker, the upstream circuit breaker starts short-circuit short-delay protection. (T1+10.1ms) Time: (Data transmission time 0.1ms) The upstream circuit breaker received the data 1, 0, 80, 80, 1, 0, 0; (T1+10.2ms) Time: (Data transmission time 0.1ms) The upstream circuit breaker received the data 2, 80, 80, 80, 0, 0, 0; (T1+10.3ms) Time: (Data transmission time 0.1ms) The upstream circuit breaker received the data 3, 80, 80, 80, 0, 0, 0; The upstream circuit breaker is calculated to have I1A' = 440 - 0 - 80 - 80 = 280A; The upstream circuit breaker sends data 1, 'A', 280 At time (T1+10.4ms) (data transmission time 0.1ms): The downstream circuit breaker 1 received data 1, 'A', 280; The downstream circuit breaker 1 detects that the address matches its own, phase 'A', buffer I1A': 280; (T1+10ms+10ms) time: (Calculate the effective value of the current every 10ms and perform current protection) The downstream circuit breaker 1 replaces I1A with 280A. Since 280A is greater than Ir2 (100A) of the downstream circuit breaker 1, short-circuit short-delay protection is initiated. (T1+10ms+10ms+100ms) time: Since the time t2 of the downstream circuit breaker 1 is 0.1s, the downstream circuit breaker 1 meets the short-circuit short-delay action condition and sends a trip signal. T1+10ms+10ms+100ms+10ms: (Approximately 10ms from the issuance of the trip signal to the circuit breaker tripping) The downstream circuit breaker 1 tripped.

[0028] Upstream circuit breaker: IA=160A, IB=160A, IC=160A; Downstream circuit breaker 1: I1A=0, I1B=0A, I1C=0A, DX1A=1, DX1B=0, DX1C=0; Downstream circuit breaker 2: I2A=80A, I2B=80A, I2C=80A, DX2A=0, DX2B=0, DX2C=0; Downstream circuit breaker 3: I3A=80A, I3B=80A, I3C=80A, DX3A=0, DX3B=0, DX3C=0; If IA, IB, and IC are all less than Ir2 (400A) of the upstream circuit breaker, the upstream circuit breaker will terminate the short-circuit short-delay protection.

[0029] Of course, in other embodiments, the circuit breaker in the system can also be a single-phase circuit breaker. In this case, the lower-level circuit breaker n sends the content n, In, and DXn, where n is the communication address, In is the single-phase current value of the circuit breaker, and DXn is the current transformer disconnection information of the circuit breaker. The upper-level circuit breaker receives the current values ​​and current transformer disconnection information of each lower-level circuit breaker via a fieldbus. Assuming the current transformer of lower-level circuit breaker 1 is disconnected, to prevent the measured current from being non-zero due to external electromagnetic interference after the transformer disconnection, it is preferable to set the current to 0. Lower-level circuit breaker 1 sets I1 to 0 and DX1 to 1, and then transmits the relevant information to the upper-level circuit breaker via the bus. When the upper-level circuit breaker receives DX1 as 1, it calculates the estimated current value of lower-level circuit breaker 1: I1' = I - I1......- In; where I1' is the estimated current value of the lower-level circuit breaker 1, I is the current detection value of the upper-level circuit breaker, I1 is the current detection value of the lower-level circuit breaker 1, and In is the current detection value of the lower-level circuit breaker n. The calculated estimated current value I1' of the lower-level circuit breaker 1 is transmitted to the lower-level circuit breaker 1 through bus communication. The downstream circuit breaker 1 uses the received I1' as its own current detection value to perform overload, short-circuit short-delay, and short-circuit instantaneous current protection, thereby restoring the current protection function.

Claims

1. A multi-level power distribution protection method, using a multi-level circuit breaker system for power distribution protection, wherein each lower-level circuit breaker in the multi-level circuit breaker system has a current transformer open-circuit detection function, and each lower-level circuit breaker is communicatively connected to its upper-level circuit breaker; characterized in that, Each downstream circuit breaker transmits its own phase current detection values ​​and current transformer open circuit detection information to the upstream circuit breaker in real time. When the upstream circuit breaker receives information from its downstream circuit breaker indicating a current transformer open circuit fault, the upstream circuit breaker estimates the current of the downstream circuit breaker with the open circuit fault by subtracting the sum of the current detection values ​​of the other normal downstream circuit breakers from its own current detection value. The upstream circuit breaker then transmits the estimated current value to the downstream circuit breaker with the open circuit fault, which uses the estimated current value as its own current detection value for current protection.

2. The multi-level power distribution protection method as described in claim 1, characterized in that, When a downstream circuit breaker detects a current transformer disconnection fault in itself, it sets the current detection value of the corresponding phase with the current transformer disconnection fault to zero and then transmits it to the upstream circuit breaker.

3. A multi-level power distribution protection device, using a multi-level circuit breaker system for power distribution protection, wherein each lower-level circuit breaker in the multi-level circuit breaker system has a current transformer disconnection detection function, and each lower-level circuit breaker is communicatively connected to its upper-level circuit breaker; characterized in that, Each downstream circuit breaker transmits its own phase current detection values ​​and current transformer open circuit detection information to the upstream circuit breaker in real time. When the upstream circuit breaker receives current transformer open circuit fault information sent by its downstream circuit breaker, the upstream circuit breaker estimates the current of the downstream circuit breaker with the current transformer open circuit fault by subtracting the sum of the current detection values ​​of the other normal downstream circuit breakers from its own current detection value. The upstream circuit breaker then transmits the estimated current value to the downstream circuit breaker with the current transformer open circuit fault, and the downstream circuit breaker with the current transformer open circuit fault uses the estimated current value as its own current detection value for current protection.

4. The multi-level power distribution protection device as described in claim 3, characterized in that, When a downstream circuit breaker detects a current transformer disconnection fault in itself, it sets the current detection value of the corresponding phase with the current transformer disconnection fault to zero and then transmits it to the upstream circuit breaker.

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