Protective relay and method for controlling a protective relay

Abstract

The protective relay includes a slope change detection relay that detects a change in the slope of the current flowing through a current transformer installed near a first circuit breaker in a DC power system, and a command output unit that outputs an open command for a second circuit breaker located near the first circuit breaker when it is determined that the open command for the first circuit breaker continues and the slope change detection relay is not operating.

Description

Technical Field

[0001] The present disclosure relates to countermeasures against breaker malfunctions implemented in protective relays installed in DC power systems.

Background Art

[0002] Generally, a protective relay that outputs a trip command to a breaker is provided to remove an accident during a transmission line accident (see Patent Documents 1 and 2).

[0003] In this regard, even if a trip command is output from the protective relay to the breaker when a system accident occurs, the breaker may not be able to properly fulfill its duty due to a defect in the breaker. When such a circuit breaker failure (CBF) occurs, equipment damage due to fault current, expansion of the accident range, widespread power outages, reduction of system stability, and spread of the accident to the entire power system may occur.

[0004] Therefore, in order to quickly remove an accident, a CBF countermeasure (circuit breaker malfunction countermeasure) function that outputs a trip command to an adjacent breaker when CBF is detected is provided.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] On the other hand, in the case of a protective relay installed in an AC power system, a trip command is output in the order of several tens of milliseconds from the occurrence of an accident. However, in the case of a protective relay installed in a DC power system, an operating time in the order of several hundred microseconds is required from the occurrence of an accident.

[0007] This disclosure has been made in consideration of the above-mentioned problems, and its main purpose is to provide a protective relay and a control method for the protective relay that can quickly respond to circuit breaker failure in a DC power system. [Means for solving the problem]

[0008] A protective relay according to a certain disclosure includes a slope change detection relay that detects a change in the slope of the magnitude of the current flowing through a current transformer installed near a first circuit breaker in a DC power system, and a command output unit that outputs an open command for a second circuit breaker in the vicinity of the first circuit breaker when it is determined that the open command for the first circuit breaker continues and the slope change detection relay is not operating.

[0009] A method for controlling a protective relay according to a certain disclosure includes the steps of detecting a change in the slope of the magnitude of the current flowing through a current transformer installed near a first circuit breaker in a DC power system, and outputting an open command for a second circuit breaker in the vicinity of the first circuit breaker when it is determined that the open command for the first circuit breaker continues and no change in the slope of the magnitude of the current has been detected. [Effects of the Invention]

[0010] The protective relay and control method for the protective relay described herein can promptly respond to circuit breaker failures in a DC power system. [Brief explanation of the drawing]

[0011] [Figure 1] This figure schematically shows an example of the configuration of a DC power system in which a protective relay equipped with a CBF (Cold Breach Fault) countermeasure function according to Embodiment 1 is installed. [Figure 2] This block diagram shows the hardware configuration of a digital protection relay device that constitutes a protection relay system according to Embodiment 1. [Figure 3] This is a block diagram showing the functional configuration of the CBF countermeasure function according to Embodiment 1. [Figure 4]This figure illustrates the current change detected by the current transformer 7 according to Embodiment 1. [Figure 5] This is a block diagram showing the functional configuration of the CBF countermeasure function according to Embodiment 2. [Figure 6] This figure illustrates the current change detected by the current transformer 7 according to Embodiment 2. [Figure 7] This block diagram shows the functional configuration of the CBF countermeasure function according to Embodiment 3. [Modes for carrying out the invention]

[0012] Each embodiment will be described in detail below with reference to the drawings. Note that the same or corresponding parts will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0013] Embodiment 1. [Power System Configuration] Figure 1 is a schematic diagram showing an example of the configuration of a DC power system equipped with a protective relay that has a CBF (Cold Breakdown Fault) countermeasure function according to Embodiment 1. Referring to Figure 1, in the DC power system, wire 1 is connected to busbar 2. Furthermore, circuit breakers 4 and 5 and a current transformer 7 are provided on wire 1. The power system in Figure 1 will be described in the case of a DC system. In addition, a circuit breaker 6 is provided on busbar 2.

[0014] The protective relay system 10 includes a main relay function 20 for detecting faults in the power system and a circuit breaker malfunction prevention function (CBF prevention function) 30.

[0015] Typically, the main relay function 20 and the CBF protection function 30 are calculated and processed by a common CPU implemented in the protective relay unit.

[0016] The main relay function 20 detects the occurrence of an accident in the power system based on the current signal CS from the current transformer 7 provided on the electric wire 1, outputs an opening command TR1 to the circuit breaker 4 when an accident is detected, and outputs an opening command TR2 to the CBF countermeasure function 30. The accident determination method by the main relay function 20 is not particularly limited. The main relay function 20 may include, for example, a current differential relay element or a distance relay element. In the case of a current differential relay element, a current signal from another current transformer (not shown) provided on the electric wire 1 is also input to the main relay function 20. In the case of a distance relay element, a voltage signal from a voltage transformer (not shown) provided on the bus bar 2 is also input to the main relay function 20.

[0017] The CBF countermeasure function 30 includes a CBF detection element (for example, reference numeral 40 in FIG. 3) for determining the presence or absence of an accident current based on the current signal CS from the current transformer 7. The CBF countermeasure function 30 outputs an opening command TR3 for shutting off the surrounding circuit breakers 5 and 6 respectively when it determines that the circuit breaker 4 fails to operate when the opening command TR2 continues even after the time required for opening the circuit breaker 4 has elapsed after receiving the opening command TR2 from the main relay function 20.

[0018] The above main relay function 20 and CBF countermeasure function 30 are configured by the digital protection relay device shown in FIG. 2.

[0019] [Hardware Configuration of Digital Protection Relay Device] FIG. 2 is a block diagram showing the hardware configuration of a digital protection relay device that constitutes a protection relay system according to Embodiment 1. Referring to FIG. 2, the digital relay device 100 (20, 30 in FIG. 1) includes an input conversion unit 101 incorporating auxiliary transformers 102_1,... and a digital relay unit 103.

[0020] The input conversion unit 101 is an input section to which the current signal acquired by the current transformer 7 in FIG. 1 is input. Each auxiliary transformer 102 converts the current signal from the current transformer 7 into a voltage signal at a voltage level suitable for signal processing in the digital relay unit 103.

[0021] The digital relay unit 103 includes analog filters (AF) 104_1,..., sample and hold circuits (S / F) 105_1,..., a multiplexer (MPX) 106, and an analog-to-digital (A / D) converter 107. The digital relay unit 103 further includes a CPU (Central Processing Unit) 108, a RAM (Random Access Memory) 109, a ROM (Read Only Memory) 110, multiple digital input (D / I) circuits 111, multiple digital output (D / O) circuits 112, and a bus 113 connecting these components.

[0022] Each analog filter 104 is provided to remove aliasing errors during A / D conversion, and is, for example, a low-pass filter. Each sample-and-hold circuit 105 samples and holds the signal that has passed through the corresponding analog filter 104 at a predetermined sampling frequency. The multiplexer 106 sequentially selects the voltage signals held by the sample-and-hold circuits 105_1,... The A / D converter 107 converts the voltage signals selected by the multiplexer into digital values. The CPU 108 operates according to a program stored in the ROM 110 and an external storage device (not shown), and performs calculations for various protection elements based on the digital data output from the A / D converter 107. The D / O circuit 112 outputs an open command to open the circuit breaker.

[0023] [Configuration and operation of CBF countermeasures function] Figure 3 is a block diagram showing the functional configuration of the CBF countermeasure function according to Embodiment 1. Referring to Figure 3, the CBF countermeasure function 30 includes a CBF detection element 40, an AND gate 43, and on-delay timers 44 and 45. The on-delay timer is a timer that outputs after a set time t has elapsed. This is realized by the execution of a program by the CPU 108 in Figure 2. It goes without saying that the above elements of the CBF countermeasure function 30 can also be realized by using a dedicated circuit instead of the CPU 108.

[0024] The CBF detection element 40 includes a tilt change detection relay 41 and a NOT gate 42, and detects the tilt change of the current signal CS from the current transformer 7 in Figure 1, compares the tilt change value with the set value, and detects a malfunction of the circuit breaker 4 based on the comparison result.

[0025] The CBF detection element 40 determines whether the slope change value of the current signal CS from the current transformer 7 in Figure 1 is below the set value, and outputs a logic level "1" signal indicating that the circuit breaker 4 is not operating if the slope change value is greater than or equal to the set value.

[0026] The slope change detection relay 41 detects the slope change value, which is the amount of change in current ΔI with respect to time Δt, and determines whether or not it is below a set value.

[0027] Specifically, it determines whether ΔI / Δt < the set value. For example, the set value may be set to 0. Note that the set value is just an example and can be set to other values.

[0028] The tilt change detection relay 41 outputs a logic level "0" signal when the tilt change value is greater than or equal to a set value, and outputs a logic level "1" signal when it is less than or equal to a set value.

[0029] The NOT gate 42 inverts the signal from the tilt change detection relay 41 and outputs it to the AND gate 43.

[0030] The AND gate 43 outputs an open command TR3 to the surrounding circuit breakers 5 and 6 via the on-delay timer 44 when the logic level of the open command TR2 from the main relay is "1" and the CBF detection element 40 has detected a circuit breaker malfunction (i.e., the logic level of the output signal of the NOT gate 42 is "1").

[0031] The on-delay timer 44 is a timer that outputs after a set time t has elapsed. In this example, the set time t for the on-delay timer 44 is set to several hundred microseconds.

[0032] The on-delay timer 45 is set to the time it takes for the slope of the current flowing through the circuit breaker 4 to change according to the open command TR2. In this example, it is set to Xms, taking into account the characteristics and variations of the circuit breaker 4.

[0033] Figure 4 illustrates the current change detected in the current transformer 7 according to Embodiment 1. Referring to Figure 4, the current I in the current transformer 7 increases over time from the point of fault occurrence. The LP operating time indicates the period during which the main relay function 20 is in operation. In this example, we will describe the case in which the slope change is determined Xms after the main relay function 20 outputs an open command TR1 to the circuit breaker 4.

[0034] Circuit breaker 4 opens the line in accordance with the opening command TR1. If there is no malfunction in circuit breaker 4, the line will open normally and the current value will begin to decrease within Xms.

[0035] On the other hand, if a malfunction occurs in the circuit breaker 4, it will not be able to properly open the line in accordance with the opening command TR1. Therefore, it is possible to detect the malfunction of the circuit breaker 4 by detecting the change in the slope value after Xms.

[0036] The CBF countermeasure function 30 determines that a malfunction has occurred in circuit breaker 4 if the slope change value after Xms is greater than or equal to the set value, and outputs an open command TR3 indicating logic level "1" to circuit breakers 5 and 6.

[0037] The circuit breakers 5 and 6 located around circuit breaker 4 open the line in accordance with the open command TR3. This CBF trip makes it possible to reduce the current value in the line where the current transformer 7 is installed. In other words, the CBF countermeasure function 30 detects a change in the slope of the current flowing through the current transformer 7 installed near circuit breaker 4 in the DC power system, and if it determines that the open command for circuit breaker 4 continues and no change in the slope of the current is detected, it outputs an open command for the circuit breakers 5 and 6 around circuit breaker 4.

[0038] This method enables high-speed CBF tripping and makes it possible to implement a circuit breaker failure countermeasure function that can handle circuit breaker failures in DC power systems.

[0039] Embodiment 2. Figure 5 is a block diagram showing the functional configuration of the CBF countermeasure function according to Embodiment 2. The CBF countermeasure function 30A in Figure 5 differs in that the CBF detection element 40 is replaced with the CBF detection element 40A. The other configurations are the same as those of the CBF countermeasure function 30 in Figure 3, so the same or corresponding parts are denoted by the same reference numerals and the description is not repeated.

[0040] The CBF detection element 40A in Figure 5 differs from the CBF detection element 40 in Figure 3 in that it includes an overcurrent detection relay 46 and an AND gate 47.

[0041] The overcurrent detection relay 46 compares the current value according to the current signal CS with the threshold Ith to determine whether it is greater than or equal to the threshold Ith.

[0042] The overcurrent detection relay 46 outputs a signal with a logic level of "1" if it determines that the current value is greater than or equal to the threshold Ith.

[0043] The AND gate 47 outputs a signal with a logic level of "1" as the output signal of the CBF detection element 40A when the logic level of the output signal of the NOT gate 42 is "1" and the logic level of the output signal of the overcurrent detection relay 46 is "1".

[0044] Therefore, the CBF detection element 40A outputs a signal based on the comparison result obtained by comparing the slope change value and the corrected value by the slope change detection relay 41, and the comparison result obtained by comparing the current value and the threshold value Ith by the overcurrent detection relay 46.

[0045] Specifically, the CBF detection element 40A determines whether the slope change value of the current signal CS is below a set value. If the slope change value is equal to or greater than the set value, and the current value is equal to or greater than the threshold Ith, it outputs a logic level "1" signal indicating that the circuit breaker is not operating.

[0046] Figure 6 illustrates the current change detected in the current transformer 7 according to Embodiment 2. Referring to Figure 6, the current I in the current transformer 7 increases over time from the point of fault occurrence. The LP operating time indicates the period during which the main relay function 20 is in operation. In this example, we will describe the case in which the slope change is determined Xms after the main relay function 20 outputs an open command TR1 to the circuit breaker 4.

[0047] As explained in Figure 4, circuit breaker 4 opens the line in accordance with the opening command TR1. If there is no malfunction in circuit breaker 4, the line opens normally and the current value begins to decrease within Xms. If there is a malfunction in circuit breaker 4, it cannot open the line normally in accordance with the opening command TR1.

[0048] The CBF countermeasure function 30A according to Embodiment 2 determines that a malfunction has occurred in circuit breaker 4 if the slope change value after Xms is equal to or greater than the set value and the current value is equal to or greater than the threshold Ith, and outputs an open command TR3 indicating logic level "1" to circuit breakers 5 and 6.

[0049] Circuit breakers 5 and 6, located around circuit breaker 4, open the line in accordance with the opening command TR3. This CBF tripping makes it possible to reduce the current value in the line where the current transformer 7 is installed.

[0050] This method enables high-speed CBF tripping and makes it possible to implement a circuit breaker malfunction countermeasure function that can respond to circuit breaker failures in abnormal DC power systems.

[0051] Embodiment 3. Figure 7 is a block diagram showing the functional configuration of the CBF countermeasure function according to Embodiment 3. The CBF countermeasure function 30B in Figure 7 differs in that the CBF detection element 40 is replaced with the CBF detection element 40B. The other configurations are the same as those of the CBF countermeasure function 30 in Figure 3, so the same or corresponding parts are denoted by the same reference numerals and the description is not repeated.

[0052] The CBF detection element 40B differs in that the AND gate 47 is replaced with an OR gate 48. In the configuration according to Embodiment 2, if the slope change value after Xms falls below the set value, the open command TR3 indicating logic level "1" is not output, even if the current value is above the threshold Ith. In this regard, if the circuit breaker 4 is not operating normally due to variations in the characteristics of the circuit breaker 4, the slope change value may fall below the set value, meaning that the current value has started to decrease but may still be high.

[0053] According to Embodiment 3, the CBF detection element 40B outputs an open command TR3 with a logic level of "1" if it determines that the slope change value is below a set value, i.e., the current value has started to decrease, but the current value is greater than or equal to the threshold Ith.

[0054] The CBF countermeasure function 30B determines that circuit breaker 4 is not operating normally if the slope change value of the CBF detection element 40B after Xms is greater than or equal to a set value, or if the current value is greater than or equal to the threshold Ith, and outputs an open command TR3 indicating logic level "1" to circuit breakers 5 and 6.

[0055] This method enables high-speed CBF tripping and makes it possible to implement a circuit breaker malfunction countermeasure function that can handle circuit breaker malfunctions in DC power systems that are not functioning properly due to variations in the characteristics of the circuit breaker 4.

[0056] In this example, the CBF detection element 40A was described as including an overcurrent detection relay 46, but this detection relay is just one example, and it is possible to combine it with other relays that detect abnormalities.

[0057] The configurations illustrated above as embodiments are examples of the configurations of this disclosure, and can be combined with other known technologies, or modified, such as by omitting parts, without departing from the gist of this disclosure. Furthermore, in the embodiments described above, processes and configurations described in other embodiments may be appropriately adopted and implemented.

[0058] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of symbols]

[0059] 1 Power line, 2 Busbar, 4, 5, 6 Circuit breaker, 7 Current transformer, 10 Protection relay system, 20 Main relay function, 30, 30A, 30B CBF protection function, 41 Tilt change detection relay, 46 Overcurrent detection relay, 100 Digital relay device, 101 Input conversion unit, 102 Auxiliary transformer, 103 Digital relay unit, 104 Analog filter, 105 Sample and hold circuit, 106 Multiplexer, 107 Analog-to-digital converter, 108 CPU, 109 RAM, 110 ROM, 111 D / I circuit, 112 D / O circuit, 113 Bus.

Claims

1. A slope change detection relay that detects changes in the slope of the current flowing through a current transformer installed near a first circuit breaker in a DC power system, A protective relay comprising: a command output unit that outputs an opening command for a second circuit breaker in the vicinity of the first circuit breaker when the opening command for the first circuit breaker continues and the tilt change detection relay determines that it has not detected a change in the tilt of the current magnitude.

2. The protective relay according to claim 1, wherein the command output unit outputs an open command for a second circuit breaker in the vicinity of the first circuit breaker when the open command is continued and the slope change detection relay determines that no change in the slope of the current magnitude is detected for a predetermined period of time.

3. The protective relay according to claim 1, wherein the command output unit outputs an open command for a second circuit breaker in the vicinity of the first circuit breaker when the open command is continued and the slope change detection relay determines that the slope of the magnitude of the current does not change to a predetermined value within a predetermined period of time.

4. The system further includes an overcurrent detection relay that detects whether the magnitude of the current in the first circuit breaker is greater than or equal to a threshold, The protective relay according to claim 1, wherein the command output unit outputs an open command for a second circuit breaker near the first circuit breaker when the open command is continued, the slope of the current magnitude does not change to a predetermined value by the slope change detection relay during a predetermined period, and the overcurrent detection relay determines that the current magnitude is greater than or equal to a threshold.

5. The system further includes an overcurrent detection relay that detects whether the magnitude of the current in the first circuit breaker is greater than or equal to a threshold, The protective relay according to claim 1, wherein the command output unit outputs an open command for a second circuit breaker near the first circuit breaker when the open command is continued and the slope of the current magnitude does not change to a predetermined value by the slope change detection relay during a predetermined period, or when the overcurrent detection relay determines that the current magnitude is above a threshold.

6. A step of detecting a change in the gradient of the magnitude of the current flowing through a current transformer installed near a first circuit breaker in a DC power system, A control method for a protective relay, comprising the step of outputting an open command for a second circuit breaker in the vicinity of the first circuit breaker when it is determined that the open command for the first circuit breaker continues and no change in the slope of the magnitude of the current is detected.

Images