Protective relay
The protective relay uses a control unit to adjust phase differences between zero-sequence voltage and current, simplifying hardware and enhancing accuracy in detecting power system abnormalities, addressing the complexity and noise issues of conventional ZCT-based systems.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- MITSUBISHI ELECTRIC CORP
- Filing Date
- 2023-04-03
- Publication Date
- 2026-06-19
AI Technical Summary
Conventional protective relays using two zero-phase current transformers (ZCTs) for reducing phase errors are complex and susceptible to noise and coupling coefficient variations, leading to inaccurate detection of abnormalities in power systems.
A protective relay with a control unit that records a first phase difference during test energization and adjusts a second phase difference during operation using an adjustment value to accurately detect ground faults in power systems with multiple distribution lines, simplifying the hardware configuration by eliminating the need for multiple ZCTs.
The solution allows for precise detection of abnormalities and reliable protective control in power systems, preventing unnecessary trips and adapting to various phase errors caused by ZCTs, while maintaining a simple hardware configuration.
Smart Images
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Abstract
Description
Technical Field
[0001] This application relates to protective relays.
Background Art
[0002] A protective relay installed in a power system to detect abnormalities such as ground faults occurring in the system and perform control to disconnect the abnormal system from the normal system determines whether to trip to operate a circuit breaker that disconnects the system based on the phase difference between the zero-phase voltage and zero-phase current of the system, and the magnitudes of the zero-phase voltage and zero-phase current. In order to reliably execute a trip for an abnormal system and prevent unnecessary trips for a system without abnormalities, it is essential for the protective relay to derive an accurate phase difference between the zero-phase voltage and zero-phase current.
[0003] Here, for a zero-phase current transformer (ZCT) for measuring zero-phase current, a phase error between its input current and output current (zero-phase current) is likely to occur due to changes in impedance characteristics when multiple such ZCTs are connected in parallel, individual differences, impedance differences from the protective relay, etc. Therefore, a method has been proposed that uses a band-stop filter, an amplifier, and two ZCTs to suppress fluctuations in the core inductance of the ZCT and reduce the phase error (see, for example, Patent Document 1).
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] However, the conventional phase error reduction method described above uses two ZCTs, with the output of the first ZCT passing through to the input side of the second ZCT. This results in a complex hardware configuration and makes it susceptible to changes in coupling coefficients, variations in ZCTs, and noise, which can cause phase errors in the detected zero-sequence current. Consequently, it is difficult to accurately detect abnormalities in the power system, and therefore, it may be impossible to perform accurate control to protect the system. This application discloses technology to solve the above-mentioned problems, and aims to provide a protective relay that can accurately detect abnormalities occurring in the power system and perform precise protective control without complicating the hardware configuration. [Means for solving the problem]
[0006] The protective relay disclosed herein is A protective relay equipped with a control unit that detects a ground fault occurring in a power system having multiple distribution lines, based on the zero-sequence voltage and the zero-sequence current flowing through each of the distribution lines, The control unit, During the test power-on. In the first mode, The first phase difference between the zero-sequence voltage and the zero-sequence current is recorded as an adjustment value. Switchable from the first mode described above. This is during actual operation. In the second mode, The second phase difference between the zero-sequence voltage and the zero-sequence current is adjusted by the adjustment value, and a ground fault in the power system is detected based on the adjusted second phase difference. It is. [Effects of the Invention]
[0007] The protective relay disclosed in this application provides a protective relay that has a simple hardware configuration while being able to accurately derive the phase difference between zero-sequence voltage and zero-sequence current. [Brief explanation of the drawing]
[0008] [Figure 1]This is a block diagram showing the schematic configuration of a protective relay according to Embodiment 1. [Figure 2] This figure shows the system configuration of the control unit of the protective relay according to Embodiment 1. [Figure 3] This is a flowchart showing the flow of automatic adjustment control performed by the control unit of the protective relay according to Embodiment 1. [Figure 4] This figure shows the waveforms of zero-sequence voltage and zero-sequence current during test energization, illustrating the automatic adjustment control performed by the control unit of the protective relay according to Embodiment 1. [Figure 5] This is a flowchart showing the flow of control operations in the adjustment value acquisition mode performed by the control unit of the protective relay according to Embodiment 2. [Figure 6] This figure shows the hardware configuration of the control unit in each embodiment. [Modes for carrying out the invention]
[0009] Embodiment 1. Embodiment 1 will be described below with reference to the drawings. In each drawing, the same reference numerals indicate the same or corresponding parts. Figure 1 is a block diagram showing the schematic configuration of the protective relay 100 according to Embodiment 1. The protective relay 100 is installed in power distribution equipment such as a switchboard (not shown) and primarily acquires and monitors the voltage and current elements of power system 1 as measurement elements. If an abnormality occurs in the monitored voltage or current elements, it performs protective control to separate the normal system from the abnormal system. In particular, one of the protective elements of the protective relay 100, ground fault protection, detects the occurrence of a ground fault caused by insulation deterioration or breakage of high-voltage cables, and performs protective control to disconnect the system where the ground fault occurred.
[0010] In addition to obtaining the zero-phase voltage of the power system 1 as the above voltage element and the zero-phase current as the above current element, the protection relay 100 derives the phase difference between the zero-phase voltage and the zero-phase current in order to determine whether the system is a sound phase system (a system in which no ground fault has occurred) or a ground fault phase system (a system in which a ground fault has occurred) in protection control. In order to accurately disconnect only the ground fault phase from the power system 1 and protect the sound phase, the derivation accuracy of this phase difference is important. As will be described below, the protection relay 100 of the present embodiment derives the phase difference between the zero-phase voltage and the zero-phase current of the power system 1, in which the influence of the phase error between the input current and the output current (zero-phase current) generated in the ZCT that detects the zero-phase current is reduced.
[0011] The protection relay 100 of the present embodiment will be described. As shown in FIG. 1, the protection relay 100 includes a zero-phase voltage input terminal 10, a zero-phase current input terminal 20, an output terminal 30, a power supply 40, and a control unit 50. Note that the power system 1 is configured to have a plurality of distribution lines not shown.
[0012] The zero-phase voltage input terminal 10 is connected to an EVT (Earthed Voltage Transformer) 2, and the zero-phase voltage of the power system 1 is input via this EVT 2. The zero-phase current input terminal 20 is connected to a ZCT 3, and the zero-phase current flowing through each distribution line constituting the power system 1 is input via this ZCT 3. The output terminal 30 outputs a control command from the control unit 50 to the circuit breaker 4. The power supply 40 supplies power to the control unit 50. Based on the input zero-phase voltage and zero-phase current, the control unit 50 determines the presence or absence of a ground fault in each distribution line constituting the power system 1, and determines whether to execute protection control.
[0013] The control unit 50 of the protection relay 100 will be described. FIG. 2 is a diagram showing the system configuration of the control unit 50 of the protection relay 100. FIG. 3 is a flowchart showing the flow of automatic adjustment control performed by the control unit 50. FIG. 4 is a diagram showing waveforms of zero-phase voltage and zero-phase current during test energization for explaining the automatic adjustment control performed by the control unit 50.
[0014] As shown in FIG. 2, the control unit 50 includes a zero-phase voltage measurement circuit 51A, a zero-phase current measurement circuit 51B, an A / D conversion unit 52, an adjustment unit 53, and a determination unit 54.
[0015] As shown in FIG. 3, first, the control unit 50 transitions its operation mode to an adjustment value acquisition mode as the first mode (steps S001, step S002: YES). This adjustment value acquisition mode is an operation mode for acquiring an adjustment value V for adjusting the phase error between the zero-phase voltage and the zero-phase current. Note that the criteria for YES and NO in step S002 will be described later.
[0016] At this time, although the power system 1 has not started actual operation, it has a configuration corresponding to actual operation, and test energization is performed using a relay tester or the like. The zero-phase voltage measurement circuit 51A and the zero-phase current measurement circuit 51B acquire analog data of the zero-phase voltage and zero-phase current of the power system 1 in this test energization via the zero-phase voltage input terminal 10 and the zero-phase current input terminal 20 (step S003). In this test energization, no ground fault has occurred in each distribution line. Then, the zero-phase voltage measurement circuit 51A and the zero-phase current measurement circuit 51B perform amplification and filter processing on the input analog data of the zero-phase voltage and zero-phase current. The A / D conversion unit 52 converts the analog data on which the filter processing has been performed into digital data.
[0017] Next, the adjustment unit 53 derives, as the adjustment value V, a first phase difference θ1 that is the phase difference between the zero-phase voltage and the zero-phase current during this test energization, which has been converted into digital data (step S004). Specifically, as shown in Figure 4, the adjustment unit 53 adjusts the first phase difference θ1 of the zero-crossing points of the zero-sequence voltage and zero-sequence current to an adjustment value V.
[0018] Next, the control unit 50 transitions its operating mode from the adjustment value acquisition mode, which is the first mode, to the error adjustment mode, which is the second mode (step S005, YES). The criteria for determining YES or NO in step S005 will be explained later. At this time, power system 1 transitions from a test power-on state to an operational state, which is the actual operating state.
[0019] The zero-sequence voltage measurement circuit 51A and the zero-sequence current measurement circuit 51B acquire analog data of the zero-sequence voltage and zero-sequence current of the power system 1 in this operating state via the zero-sequence voltage input terminal 10 and the zero-sequence current input terminal 20 (step S006). The zero-sequence voltage measurement circuit 51A and the zero-sequence current measurement circuit 51B then amplify and filter the input zero-sequence voltage and zero-sequence current analog data. The A / D conversion unit 52 converts the filtered analog data into digital data.
[0020] Next, the adjustment unit 53 derives a second phase difference θ2, which is the phase difference between the zero-sequence voltage and zero-sequence current in this operating state converted into digital data, and performs automatic adjustment control to adjust this second phase difference θ2 by the adjustment value V (step S007). Specifically, in this automatic adjustment control, the adjustment unit 53 removes the phase error between the input current and output current (zero-sequence current) of the ZCT from the second phase difference θ2 by subtracting the adjustment value V from the second phase difference θ2.
[0021] Based on the second phase difference θ2 adjusted in step S007, the determination unit 54 detects the presence or absence of a ground fault in each distribution line and determines whether or not to perform protective control to disconnect the distribution line where the ground fault has occurred from the healthy distribution line. When protective control is performed, the determination unit 54 activates the contacts of the output terminal 30 as a control command, causing the circuit breaker 4 to trip.
[0022] The YES and NO determinations in steps S002 and S005 may be made, for example, based on signals input from an external source according to the operating status of power system 1. For example, if the signal input from an external source indicates the test power-on state of power system 1 before operation, the determination in step S002 will be YES, and the determination in step S005 will be NO. In contrast, if the signal input from the outside indicates that power system 1 is in operation, the determination in step S002 will be NO, and the determination in step S005 will be YES.
[0023] As described above, a test power supply is performed in an operating state with a configuration corresponding to actual operating conditions, and the adjustment value V is obtained. That is, the obtained adjustment value V is obtained based on the configuration of power system 1 which is equivalent to the configuration when power system 1 is in actual operation. Therefore, the adjustment value V corresponds to various phase errors caused by ZCTs, such as changes in impedance characteristics when multiple ZCTs are connected in parallel, individual differences between them, and phase errors of ZCTs such as the impedance difference between ZCTs and protective relays. Because this adjustment value V is used to automatically adjust the second phase difference θ2 in actual operating conditions, the protective relay 100 of this embodiment can handle various phase errors caused by the ZCT. As a result, the protective relay 100 of this embodiment can accurately detect abnormalities occurring in the power system 1, ensure reliable tripping of distribution lines where abnormalities have occurred, and prevent unnecessary tripping of distribution lines where no abnormalities have occurred.
[0024] According to the protective relay of this embodiment configured as described above, A protective relay equipped with a control unit that detects a ground fault occurring in a power system having multiple distribution lines, based on the zero-sequence voltage and the zero-sequence current flowing through each of the distribution lines, The control unit, In the first mode, The first phase difference between the zero-sequence voltage and the zero-sequence current is recorded as an adjustment value. In the second mode, which is switched from the first mode, The second phase difference between the zero-sequence voltage and the zero-sequence current is adjusted by the adjustment value, and a ground fault in the power system is detected based on the adjusted second phase difference. It is.
[0025] Thus, the first phase difference between the zero-sequence voltage and zero-sequence current obtained in the first mode is recorded as an adjustment value. Then, the second phase difference between the zero-sequence voltage and zero-sequence current obtained in the subsequent second mode is adjusted using the above adjustment value. Therefore, by configuring the power system in the first mode to address various factors that may cause phase errors in the ZCT, the second phase difference in the subsequent second mode can be adjusted with greater precision.
[0026] Furthermore, since there is no need to use multiple ZCTs to reduce phase errors in the ZCT, and the phase error is automatically adjusted by the control unit 50, the hardware configuration can be simplified. As no hardware modifications are required, it is possible to adapt to existing protective relays by changing the processing of the control unit, enabling highly accurate detection of system anomalies and precise protective control.
[0027] Furthermore, the control unit 50 may record the adjustment value V for each distribution line in the adjustment value acquisition mode, and adjust the second phase difference θ2 derived for each distribution line using the corresponding adjustment value V for the distribution line. This makes it possible to derive a second phase difference θ2 with reduced errors for each distribution line.
[0028] Embodiment 2. Hereinafter, Embodiment 2 of the present application will be described with reference to the figures, focusing on the differences from Embodiment 1 described above. Parts similar to those in Embodiment 1 are denoted by the same reference numerals and their description is omitted. In Embodiment 1, the input values such as current during test energization in the adjustment value acquisition mode were constant values set to rated values, etc. However, it is known that the phase error of the ZCT also fluctuates depending on the input current value. Therefore, in order to perform more accurate protection control, it is necessary to vary the adjustment value V according to the input current value.
[0029] Figure 5 is a flowchart showing the flow of control operations in the adjustment value acquisition mode performed by the control unit 50. In this embodiment, three types of adjustment values V are acquired. Specifically, in the adjustment value acquisition mode, the input value of the zero-sequence current input to the zero-sequence current input terminal 20 is varied in three stages: small, medium, and large, and three types of adjustment values V are acquired and recorded (steps S003A, S004A, S003B, S004B, S003C, and S004C). In this case, the input voltage applied to the zero-sequence voltage input terminal should be constant (approximately the rated value). Note that the zero-sequence current input value input to the zero-sequence current input terminal 20 is assumed to be medium for the rated value, small for less than or equal to the rated value, and large for greater than or equal to the rated value.
[0030] The adjustment unit 53 calculates an adjusted second phase difference θ2 by adjusting the phase error from the second phase difference θ2 measured in the operating state of the power system 1 and the adjustment value V. The adjustment value V used when adjusting the second phase difference θ2 is the adjustment value V recorded corresponding to the zero-sequence current of the magnitude corresponding to the magnitude of the zero-sequence current when the second phase difference was derived, from among the three types of adjustment values V obtained. That is, if the input value of the zero-sequence current when the second phase difference θ2 was derived is large, the adjustment value V obtained when the input value of the zero-sequence current is large is used.
[0031] According to the protective relay of this embodiment configured as described above, The control unit, In the previous mode 1, The magnitude of the zero-sequence current flowing through the distribution line is varied in multiple stages, and the adjustment value is recorded for each of the multiple-stage varied zero-sequence currents. The second phase difference is adjusted using the adjustment value recorded in accordance with the zero-sequence current in the first mode, which has a magnitude corresponding to the magnitude of the zero-sequence current from which the second phase difference was derived. It is.
[0032] Thus, the protective relay of this embodiment acquires multiple phase error adjustment values in a state corresponding to the actual usage configuration before the equipment is put into operation. Therefore, it can accommodate phase errors that fluctuate depending on the input value of the ZCT, and as a result, it becomes possible to detect the presence or absence of a ground fault with high accuracy.
[0033] Figure 6 shows the hardware configuration of the control unit 50. The control unit 50, as an example of its hardware, consists of a processor 60 and a storage device 70, as shown in Figure 6. The storage device 70 includes a volatile storage device such as random access memory (not shown) and a non-volatile auxiliary storage device such as flash memory. Alternatively, a hard disk may be provided as an auxiliary storage device instead of flash memory. The processor 60 executes the program input from the storage device 70. In this case, the program is input to the processor 60 from the auxiliary storage device via the volatile storage device. The processor 60 may also output data such as calculation results to the volatile storage device of the storage device 70, or it may save the data to the auxiliary storage device via the volatile storage device.
[0034] Although this application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but can be applied individually or in various combinations to the embodiments. Accordingly, countless variations not illustrated are conceivable within the scope of the art disclosed herein. These include, for example, modifying, adding or omitting at least one component, or even extracting at least one component and combining it with components of other embodiments.
[0035] The various aspects of this disclosure are summarized below as an appendix.
[0036] (Note 1) A protective relay equipped with a control unit that detects a ground fault occurring in a power system having multiple distribution lines, based on the zero-sequence voltage and the zero-sequence current flowing through each of the distribution lines, The control unit, In the first mode, The first phase difference between the zero-sequence voltage and the zero-sequence current is recorded as an adjustment value. In the second mode, which is switched from the first mode, The second phase difference between the zero-sequence voltage and the zero-sequence current is adjusted by the adjustment value, and a ground fault in the power system is detected based on the corrected second phase difference. Protective relay. (Note 2) The control unit, In the previous mode 1, The magnitude of the zero-sequence current flowing through the distribution line is varied in multiple stages, and the adjustment value is recorded for each of the multiple-stage varied zero-sequence currents. The second phase difference is adjusted using the adjustment value recorded in accordance with the zero-sequence current in the first mode, which has a magnitude corresponding to the magnitude of the zero-sequence current from which the second phase difference was derived. The protective relay described in Appendix 1. (Note 3)) The control unit, In the first mode, the adjustment value is determined for each power distribution line and recorded. In the second mode, the second phase difference is derived for each of the distribution lines, The derived second phase difference is adjusted by the adjustment value of the corresponding power distribution line. The protective relay described in Appendix 1 or Appendix 3. (Note 4) In the first mode, the power system is configured such that no ground faults occur in the distribution lines. A protective relay as described in any one of the notes 1 through 3. (Note 5) The switching between the first mode and the second mode is performed based on a signal indicating the operating status of the power system. A protective relay as specified in any one of the appendices 1 through 4. [Explanation of symbols]
[0037] 1 power system, 50 control unit, 100 protective relay.
Claims
1. A protective relay equipped with a control unit that detects a ground fault occurring in a power system having multiple distribution lines, based on the zero-sequence voltage and the zero-sequence current flowing through each of the distribution lines, The control unit, During the first mode, which is the test power-on period, The first phase difference between the zero-sequence voltage and the zero-sequence current is recorded as an adjustment value. In the second mode, which is the actual operating mode to which the user switches from the first mode, The second phase difference between the zero-sequence voltage and the zero-sequence current is adjusted by the adjustment value, and a ground fault in the power system is detected based on the adjusted second phase difference. Protective relay.
2. The control unit, In the first mode, The magnitude of the zero-sequence current flowing through the distribution line is varied in multiple stages, and the adjustment value is recorded for each of the multiple-stage varied zero-sequence currents. The second phase difference is adjusted using the adjustment value recorded in correspondence to the zero-sequence current in the first mode, which has a magnitude corresponding to the magnitude of the zero-sequence current from which the second phase difference was derived. The protective relay according to claim 1.
3. The control unit, In the first mode, the adjustment value is determined for each power distribution line and recorded. In the second mode, the second phase difference is derived for each of the power distribution lines, The derived second phase difference is adjusted by the adjustment value of the corresponding power distribution line. A protective relay according to claim 1 or claim 2.
4. In the first mode, the power system is in a state where no ground faults occur in the distribution lines. A protective relay according to claim 1 or claim 2.
5. The switching between the first mode and the second mode is performed based on a signal indicating the operating status of the power system. A protective relay according to claim 1 or claim 2.