WO2022044278A1

WO2022044278A1 - Digital protective relay and digital protective relay monitoring system

Info

Publication number: WO2022044278A1
Application number: PCT/JP2020/032683
Authority: WO
Inventors: 裕紀多田羅
Original assignee: 三菱電機株式会社
Priority date: 2020-08-28
Filing date: 2020-08-28
Publication date: 2022-03-03
Also published as: CN115885443A; TWI743010B; JPWO2022044278A1; KR20230034393A; TW202209778A; JP6840306B1

Abstract

Provided is a digital protective relay (1) that inputs an alternating current flowing through a transformer (3) and that performs a cutoff operation of a circuit breaker (2) connected to the transformer (3) when an overcurrent is detected, the digital protective relay (1) comprising: a control unit (14) that blocks the cutoff operation of the circuit breaker when a proportion (second harmonic content) of an extracted second harmonic included in an excitation inrush current is at least a defined threshold value; a threshold value learning unit (15) that updates the threshold value on the basis of the extracted second harmonic content every time the circuit breaker (2) is inserted and the transformer (3) is connected; and a storage unit (16) that stores the excitation inrush current and the second harmonic content together with a calculated time, wherein the threshold value learning unit (15), on the basis of the excitation inrush current and the second harmonic content stored in the storage unit (16) and a newly input excitation inrush current and a second harmonic content corresponding thereto, calculates a change over time for both the excitation inrush current and the second harmonic content, including a future predicted value. A monitoring device (20) connected to the digital protective relay (1) displays the changes over time.

Description

Digital protected relay and digital protected relay monitoring system

This disclosure relates to digital protected relays and digital protected relay monitoring systems.

Digital protected relays are used to protect, for example, transformers in the power system. Various malfunction preventions have been studied in conventional digital protected relays. For example, in order to distinguish between the exciting inrush current that flows when a transformer or the like is connected to the system and the failure current at the time of system failure, the second harmonic component included in the input signal is detected and the ratio to the fundamental wave component. When exceeds the threshold value, it is determined that the exciting inrush current is determined, and it is known that the overcurrent protection operation of the relay when dealing with the fault current is prevented.

However, since the harmonic component included in the exciting inrush current is different for each transformer, even if the threshold value is uniquely determined as in the past, there is a possibility of malfunction when the transformer is connected. On the other hand, the applicant has proposed a highly reliable digital protected relay that has a learning function of learning the exciting inrush current at the time of connecting a transformer and setting a threshold value and does not cause a malfunction (for example, Patent Document). 1).

International Publication No. 2019/043910

However, in the learning of the threshold value in Patent Document 1, since the learning period is set and sampling is performed during that period to update the threshold value, the data used is limited. Further, although the accuracy is to be improved by taking the average value of the accumulated data, a method of setting a more reliable threshold value is expected.

This disclosure is made to solve the above-mentioned problems, and it is possible to accumulate the measured excitation inrush current and the second harmonic component and calculate the change with time including the future predicted value from the data. The purpose is to provide a possible digital protected relay, and to provide a digital protected relay monitoring system that can visualize changes over time to monitor the digital protected relay and grasp the deterioration status of the equipment connected to the digital protected relay. And.

The digital protection relay according to the present disclosure is a digital protection relay that inputs an AC current flowing through a transformer and cuts off a breaker connected to the transformer when an overcurrent is detected, and the input AC current. A / D conversion unit that samples at regular time intervals, an arithmetic processing unit that performs frequency analysis from the digital values sampled by the A / D conversion unit, and an excitation plunge of the second harmonic extracted by the arithmetic processing unit. A control unit that blocks the cutoff operation of the breaker when the ratio included in the current is equal to or higher than a predetermined threshold, and a first extracted by the arithmetic processing unit each time the breaker is turned on and the transformer is connected. The threshold learning unit that updates the threshold based on the ratio included in the excitation inrush current of the second harmonic, the excitation inrush current used for the threshold update in the threshold learning unit, and the ratio included in the excitation inrush current of the second harmonic. The threshold learning unit includes a storage unit that stores the calculated time together with the calculated time, and the threshold learning unit includes the ratio included in the excitation inrush current and the excitation inrush current of the second harmonic stored in the storage unit, and the breaker is turned on. Excitation inrush current including future predicted value based on the newly input exciting inrush current when the transformer is connected and the ratio included in the exciting inrush current of the second harmonic extracted by the arithmetic processing unit. And the ratio included in the excitation inrush current of the second harmonic, the change with time is calculated.

The digital protected relay monitoring system according to the present disclosure includes the digital protected relay and a monitoring device connected to the digital protected relay, and the monitoring device is calculated by the threshold learning unit of the digital protected relay. It displays the time course of each of the ratios included in the exciting inrush current including the future predicted value and the exciting inrush current of the second harmonic.

According to the digital protected relay of the present disclosure, the ratio included in the input exciting inrush current and the excitation inrush current of the second harmonic is stored and accumulated, and the future change with time is predicted from the data, so that the future prediction can be made. It is possible to set the threshold value based on the change over time including the result, and it is possible to further improve the reliability of the digital protected relay.

Further, according to the digital protected relay monitoring system according to the present disclosure, the change over time including the predicted value of the excitation inrush current and the ratio included in the exciting inrush current of the second harmonic is visualized. Not only monitoring but also the deterioration status of equipment such as transformers connected to digital protective relays can be grasped.

It is a circuit block diagram which applied the digital protection relay which concerns on Embodiment 1 to the transformer for electric power. It is a functional block diagram of the digital protection relay and the digital protection relay monitoring system which concerns on Embodiment 1. FIG. It is a hardware block diagram of the digital protection relay and the digital protection relay monitoring system which concerns on Embodiment 1. FIG. It is a figure explaining the use state of the monitoring apparatus which concerns on Embodiment 1. FIG. It is a figure which shows the example of the time-dependent change of the excitation inrush current displayed in the monitoring apparatus which concerns on Embodiment 1. FIG. It is a figure which shows the example of the time-dependent change of the 2nd harmonic content of the excitation inrush current displayed in the monitoring apparatus which concerns on Embodiment 1. FIG.

Hereinafter, the present embodiment will be described with reference to the drawings. In each figure, the same reference numerals indicate the same or corresponding parts.

Embodiment 1.
Hereinafter, the digital protected relay and the digital protected relay monitoring system according to the first embodiment will be described with reference to the drawings.
FIG. 1 is a circuit configuration diagram in which the digital protected relay 1 according to the first embodiment is applied to a transformer 3 for electric power. In FIG. 1, a transformer 3 to be protected is connected to a power system power supply (not shown) via a circuit breaker 2 (CB: Circuit Breaker). Further, a main current transformer 4 (CT: Circuit Transformer) for extracting the alternating current of each phase is provided. The low voltage side of the transformer 3 is connected to a load (not shown) via a no-fuse breaker (MCCB: Molded Case Circuit Breaker) 5a and 5b. The alternating current extracted by the main current transformer 4 is input to the digital protected relay 1, and if it is determined to be an overcurrent (failure current) generated due to a system failure or the like, the transformer is transformed by performing a cutoff operation of the circuit breaker 2. The vessel 3 is protected.

FIG. 2 is a functional block diagram of the digital protected relay 1 and the digital protected relay monitoring system 100 according to the first embodiment. In FIG. 2, the alternating current extracted by the main current transformer 4 is converted into an appropriate magnitude by the current measuring unit 11. The A / D conversion unit 12 samples the alternating current converted by the current measurement unit 11 at regular time intervals and converts it into digital data. The digital data is input to the arithmetic processing unit 13, and frequency analysis is performed by digital arithmetic such as FFT (Fast Fourier Transform) or digital addition / subtraction processing. As a result of the frequency analysis, when the ratio of the second harmonic to the fundamental wave component of the current is equal to or higher than the threshold value, the control unit 14 determines that it is an exciting inrush current and executes the circuit breaker 2 breaking operation.

The threshold learning unit 15 performs a series of learning procedures from the generation of the excitation inrush current to the threshold calculation. The learned threshold value is transmitted to the control unit 14, and the control unit 14 determines the threshold value of the ratio of the second harmonic to the fundamental wave component of the current used for determining the excitation inrush current (hereinafter referred to as the second harmonic content). Updated as. The frequency analysis result calculated by the arithmetic processing unit 13 and the learning result by the threshold value learning unit 15 are stored and stored in the storage unit 16 which is a non-volatile memory. Further, although details will be described later, the threshold value learning unit 15 calculates future predicted values of the excitation inrush current and the second harmonic content using the data stored in the storage unit 16. The data stored in the storage unit 16 is transmitted to the monitoring device 20 outside the digital protected relay 1 via the communication unit 17. Here, the digital protected relay monitoring system 100 includes the monitoring device 20 outside the digital protected relay 1.

FIG. 3 is a configuration diagram showing an example of the hardware of the digital protected relay 1 and the digital protected relay monitoring system 100 according to the first embodiment. The current measuring unit 11 in the digital protected relay 1 is composed of an analog circuit, except for the A / D conversion unit 12, the arithmetic processing unit 13, the control unit 14, the threshold learning unit 15, the storage unit 16, and the communication unit. 17 is composed of at least a processor 101 and a storage device 102. Similarly, the digital protected relay monitoring system 100 is also composed of at least a processor 101 and a storage device 102. Although not shown, the storage device 102 includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. Further, the auxiliary storage device of the hard disk may be provided instead of the flash memory. The processor 101 executes a program input from the storage device 102, performs sampling, frequency analysis by FFT, and the like. In this case, the program is input from the auxiliary storage device to the processor 101 via the volatile storage device. Further, the processor 101 may output data such as a calculation result to the volatile storage device of the storage device 102, or may store the data in the auxiliary storage device via the volatile storage device. The threshold learning function described later may also be stored as a program in the storage device 102 and executed by the processor 101. Further, depending on the circuit configuration, a configuration may be configured in which a part of the processor is combined with an ASIC (Application Specific Integrated Circuit).

Next, the operation of the threshold value learning unit 15 and the monitoring device 20 will be described.
The main current transformer 4 constantly measures an alternating current, and the measured alternating current is input to the current measuring unit 11. Each time the circuit breaker 2 is turned on and the transformer 3 is connected to the system, the main current transformer 4 measures the alternating current as an exciting inrush current and inputs it to the current measuring unit 11. The signal converted to an appropriate size by the current measuring unit 11 is converted into digital data by the A / D conversion unit 12. The digital data input to the arithmetic processing unit 13 is subjected to frequency analysis, the second harmonic is extracted, and the second harmonic content is calculated. The calculated second harmonic content is input to the control unit 14 and the threshold value learning unit 15. The excitation inrush current is input to the threshold value learning unit 15 as well as the second harmonic content. The excitation inrush current and the second harmonic content input to the threshold value learning unit 15 are stored in the storage unit 16 together with the calculated time of the data.

The threshold value learning unit 15 updates the threshold value based on the excitation inrush current and the second harmonic content input this time, and transmits the threshold value to the control unit 14. Further, the change with time is predicted from the excitation inrush current and the second harmonic content input this time and the excitation inrush current and the second harmonic content stored in the storage unit 16.

The data of the excitation inrush current and the second harmonic content stored in the storage unit 16 and the time-dependent change of the excitation inrush current and the second harmonic content predicted by the threshold learning unit 15 are referred to by the communication unit 17. It is transmitted to the monitoring device 20 via.

FIG. 4 is a diagram illustrating a usage state of the monitoring device 20. The monitoring device 20 is a terminal such as a PC (personal computer) or a tablet, and the data transmitted from the digital protected relay 1 is displayed on the display screen thereof. The user who uses the digital protected relay 1 can monitor the operating status of the digital protected relay 1 from the displayed information such as the excitation inrush current and the change over time of the second harmonic content. Further, it is possible to predict the aging deterioration of the transformer 3 and the load, and it is possible to perform maintenance before the accident occurs due to the aging deterioration of the transformer 3 and the load. Therefore, the equipment can be operated more stably.

Next, a method of predicting the change with time of the excitation inrush current and the ratio of the second harmonic will be described with reference to the data displayed on the monitoring device 20.
5 and 6 are diagrams showing an example of data displayed on the monitoring device 20, FIG. 5 is an example of the change over time of the exciting inrush current, and FIG. 6 is a time change of the second harmonic content of the exciting inrush current. It is a figure which shows the example of. In FIGS. 5 and 6, the solid line is the actual data calculated by the digital protected relay 1, and the broken line is the future predicted value.

The applicant has obtained the following information by analyzing the excitation inrush current measured by the digital protected relay 1. The excitation inrush current increases due to aged deterioration of the transformer and load, but the current value of the second harmonic component does not change at a constant value. Also, these data fluctuate linearly over time. Therefore, as the change with time, the magnitude of the excitation inrush current increases, but the second harmonic content tends to decrease.
Based on this tendency, the simple moving average method is used to calculate the future prediction data of the excitation inrush current and the second harmonic content from the average value of the actual data.

The simple moving average method is expressed by the following formula, and the future prediction data is calculated by using the data average values of n immediately preceding (n is a natural number of 2 or more).

In the case of n≤3, it is provisional using a preset threshold value and a linear function with reference to the transformer of the same model or the state of the load connected to the transformer of the same model. Create a predicted diagram of changes over time. When n> 3, the prediction data by the simple moving average method is created. At this time, after calculating the n + 1st prediction data, the calculation of the n + 2nd prediction data is repeated using the n + 1 data average values including the n + 1th prediction data, and a prediction diagram of the change with time is created.
When the transformer 3 is connected to the system and a new exciting inrush current and a second harmonic content are acquired, the predicted diagram of the change with time is updated using the new data.

Users who use the digital protected relay 1 can see the updated excitation inrush current and second harmonic content over time each time the transformer 3 is connected to the grid and acquires a new exciting inrush current and second harmonic. It becomes possible to confirm the predicted diagram of the above with the monitoring device 20. Further, the user can directly set and change the threshold value set in the control unit 14 of the digital protected relay 1 from the change with time of the second harmonic content. The threshold value may be set by using the setting function normally provided in the digital protected relay 1.

Further, the user who uses the digital protected relay 1 is scheduled to perform harsh operation such that the transformer 3 and the load deteriorate according to the operation plan of the transformer 3 connected to the digital protected relay 1 and the load. Can adjust the threshold value itself or the coefficient for calculating the threshold value so that the threshold value becomes smaller. As a result, the digital protected relay 1 can be set to operate reliably.

As described above, the user using the digital protected relay 1 can see the updated excitation inrush current and the predicted change of the second harmonic content over time displayed on the monitoring device 20 from the transformer 3 and the load. It is possible to predict the deterioration of. Equipment management will be easier, such as accelerating the maintenance plan if the slope of the forecast diagram increases moment by moment, and reviewing the maintenance plan if the tilt of the forecast diagram becomes gentle.

Although the explanation of the threshold setting and updating method is omitted, the initial value may be updated after using the value predetermined from the actual results of the transformer of the same model. Every time the transformer 3 is connected to the system and a new exciting inrush current and the second harmonic content are acquired, the acquired second harmonic content may be multiplied by a coefficient and set. The calculation method disclosed in Publication No. 2019/043910 may be used.

Further, every time the circuit breaker 2 is turned on and the transformer 3 is connected to the system, the AC current is measured as an exciting inrush current, the threshold value learning unit 15 calculates the threshold value, and the transformer unit 14 transmits it to the storage unit 16. The data is accumulated in the circuit breaker, but the trigger for the circuit breaker 2 to be turned on and the transformer 3 to be connected to the system is used when the digital protected relay 1 itself generates the operation signal of the circuit breaker 2.

As described above, according to the first embodiment, in the digital protected relay 1 according to the present embodiment, the arithmetic processing unit 13 calculates the second harmonic content based on the input exciting inrush current, and the threshold value learning is performed. Since the threshold value is calculated by the unit 15 and the threshold value of the control unit 14 is updated, it is possible to set the threshold value according to the change with time. Further, the exciting inrush current and the second harmonic content are stored and stored in the storage unit 16 together with the calculated time, and the accumulated data and the newly calculated exciting inrush current and the second harmonic are stored in the threshold learning unit 15. Based on the wave content, future changes over time are predicted and calculated. Since the monitoring device 20 outside the digital protected relay 1 acquires and displays the change over time including the data stored in the storage unit 16 and the future predicted value calculated by the threshold learning unit 15, the digital protected relay is displayed. The user of 1 can confirm the visualized data and directly input the change of the threshold value to the digital protected relay 1.

Further, the digital protected relay monitoring system 100 according to the present embodiment visualizes changes over time including data on the excitation inrush current and the second harmonic content stored in the digital protected relay 1 and their future predicted values. Since it is provided to the user, not only the monitoring of the digital protected relay 1 but also the deterioration state of the equipment such as the transformer 3 connected to the digital protected relay can be grasped. Furthermore, it becomes possible to reasonably plan the maintenance of the equipment from the deteriorated state of the equipment.

The present disclosure describes various exemplary embodiments and examples, although the various features, embodiments, and functions described in one or more embodiments are those of a particular embodiment. It is not limited to application, but can be applied to embodiments alone or in various combinations.
Therefore, innumerable variations not illustrated are envisioned within the scope of the techniques disclosed herein. For example, it is assumed that at least one component is modified, added or omitted, and further, at least one component is extracted and combined with the components of other embodiments.

1: Digital protected relay, 2: Circuit breaker, 3: Transformer, 4: Main current transformer, 5a, 5b: No fuse breaker, 11: Current measurement unit, 12: A / D conversion unit, 13: Arithmetic processing unit , 14: Control unit, 15: Threshold learning unit, 16: Storage unit, 17: Communication unit, 20: Monitoring device, 100: Digital protected relay monitoring system, 101: Processor, 102: Storage device

Claims

A digital protective relay that inputs an alternating current flowing through a transformer and cuts off the circuit breaker connected to the transformer when an overcurrent is detected.
A / D converter that samples the input AC current at regular time intervals,
An arithmetic processing unit that performs frequency analysis from digital values sampled by the A / D conversion unit.
A control unit that prevents the circuit breaker from breaking when the ratio included in the exciting inrush current of the second harmonic extracted by the arithmetic processing unit is equal to or greater than a predetermined threshold value.
A threshold learning unit that updates the threshold value based on the ratio included in the exciting inrush current of the second harmonic extracted by the arithmetic processing unit each time the circuit breaker is turned on and the transformer is connected.
The threshold learning unit is provided with a storage unit that stores the ratio included in the excitation inrush current used for threshold update and the excitation inrush current of the second harmonic together with the calculated time.
The threshold learning unit is newly input when the breaker is turned on and the transformer is connected to the ratio included in the exciting inrush current and the exciting inrush current of the second harmonic stored in the storage unit. It is included in the exciting inrush current including the future predicted value and the exciting inrush current of the second harmonic based on the exciting inrush current and the ratio included in the exciting inrush current of the second harmonic extracted by the arithmetic processing unit. A digital protection relay that calculates the change over time for each ratio.
The digital protection according to claim 1, wherein in the threshold learning unit, a simple moving average method is used to calculate changes over time in the exciting inrush current including the future predicted value and the ratio included in the exciting inrush current of the second harmonic. relay.
The threshold learning unit is included in the newly input exciting inrush current and the exciting inrush current of the second harmonic extracted by the arithmetic processing unit each time the circuit breaker is turned on and the transformer is connected. The digital protection relay according to claim 1 or 2, wherein the change with time of each of the excitation inrush current including the future predicted value and the ratio included in the excitation inrush current of the second harmonic is calculated and updated based on the above.
The digital protected relay according to any one of claims 1 to 3.
A monitoring device connected to the digital protective relay is provided.
The monitoring device is a digital protective relay that displays changes over time in the excitation inrush current including the future predicted value calculated by the threshold learning unit of the digital protection relay and the ratio included in the excitation inrush current of the second harmonic. Monitoring system.