Digital protection relay and digital protection relay monitoring system

Abstract

The digital protection relay (1) of the present invention inputs an AC current flowing through a transformer (3), and performs a disconnection operation of a circuit breaker (2) connected to the transformer (3) when an overcurrent is detected. The digital protection relay (1) includes: a control unit (14) that prevents the disconnection operation of the circuit breaker when the ratio of the extracted second harmonic contained in the excitation impulse current (second harmonic content ratio) is greater than a predetermined threshold value; a threshold learning unit (15) that updates the threshold value according to the extracted second harmonic content ratio each time the circuit breaker (2) is turned on and the transformer (3) is connected; and a storage unit (16) that stores the excitation impulse current and the second harmonic content ratio together with the time when they are calculated. The threshold learning unit (15) calculates the time-dependent changes of the excitation impulse current and the second harmonic content ratio including future predicted values ​​based on the excitation impulse current and the second harmonic content ratio stored in the storage unit (16) and the newly input excitation impulse current and the second harmonic content ratio corresponding thereto. A monitoring device (20) connected to the digital protection relay (1) displays this.

Description

Technical Field

[0001] The present disclosure relates to a digital protection relay and a digital protection relay monitoring system. Background Art

[0002] Digital protection relays are used to protect transformers in power systems. In existing digital protection relays, various malfunction prevention measures are being studied. For example, it is known that in order to distinguish between the excitation surge current flowing when a transformer is connected to a system and the fault current when a system fault occurs, the second harmonic component contained in the input signal is detected, and when the ratio of the second harmonic component to the fundamental component exceeds a threshold value, it is determined to be an excitation surge current, and the overcurrent protection action of the relay in response to the fault current is not performed.

[0003] However, since the harmonic components contained in the excitation surge current of each transformer are different, even if the threshold is determined uniquely as in the past, it is possible that the transformer will malfunction when connected. In response to this, the applicant has proposed a digital protection relay with high reliability that has a function of learning the excitation surge current when the transformer is connected and setting the threshold learning function, and does not cause malfunction (for example, refer to patent document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2019 / 043910 Summary of the invention

[0007] Technical problem to be solved by the invention

[0008] However, regarding the threshold learning in Patent Document 1, the data used is limited because a learning period is set and sampling is performed during the period to update the threshold. In addition, although the accuracy is improved by obtaining the average value of the accumulated data, a method for setting a threshold with higher reliability is desired.

[0009] The present disclosure is proposed to solve the above-mentioned problems, and is characterized in that it provides a digital protection relay that can accumulate the measured excitation impulse current and second harmonic components, calculate the changes over time including future predicted values ​​based on the data, and provides a digital protection relay monitoring system that can visualize the changes over time, monitor the digital protection relay, and grasp the degradation status of the equipment connected to the digital protection relay.

[0010] Technical means for solving technical problems

[0011] The digital protection relay involved in the present disclosure inputs an alternating current flowing through a transformer, and when an overcurrent is detected, performs a disconnection action of a circuit breaker connected to the transformer. The digital protection relay comprises:

[0012] an A / D conversion unit that samples the input AC current at a certain time interval; an operation processing unit that performs frequency analysis based on the digital value sampled by the A / D conversion unit; a control unit that prevents the circuit breaker from disconnecting when the ratio of the second harmonic extracted by the operation processing unit to the excitation impulse current is greater than a predetermined threshold; a threshold learning unit that updates the threshold based on the ratio of the second harmonic extracted by the operation processing unit to the excitation impulse current each time the circuit breaker is turned on and the transformer is connected; and a storage unit that stores the excitation impulse current and the ratio of the second harmonic to the excitation impulse current used for threshold update in the threshold learning unit together with the time when these are calculated,

[0013] The threshold learning unit calculates the temporal changes of the excitation impulse current and the ratio of the second harmonic contained in the excitation impulse current including future predicted values ​​based on the excitation impulse current and the ratio of the second harmonic contained in the excitation impulse current stored in the storage unit, and the excitation impulse current newly input when the circuit breaker is turned on and the transformer is connected and the ratio of the second harmonic contained in the excitation impulse current extracted by the calculation processing unit.

[0014] The digital protective relay monitoring system involved in the present disclosure includes the digital protective relay and a monitoring device connected to the digital protective relay, and the monitoring device displays the changes over time of the excitation impulse current containing future predicted values ​​and the proportion of the second harmonic contained in the excitation impulse current calculated by the threshold learning unit of the digital protective relay.

[0015] Effects of the Invention

[0016] According to the digital protection relay disclosed in the present invention, the input excitation impulse current and the proportion of the second harmonic contained in the excitation impulse current are saved and accumulated, and future changes over time are predicted based on the data. Therefore, the threshold value can be set based on the changes over time including the future prediction results, which can further improve the reliability of the digital protection relay.

[0017] In addition, the digital protection relay monitoring system involved in the present disclosure can visualize the changes over time in the predicted values ​​of the excitation impulse current and the proportion of the second harmonic contained in the excitation impulse current. Therefore, it is not only possible to monitor the digital protection relay, but also to understand the degradation status of equipment such as transformers connected to the digital protection relay. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a circuit configuration diagram in which the digital protective relay according to the first embodiment is applied to a power transformer.

[0019] Figure 2 This is a functional block diagram of the digital protective relay and the digital protective relay monitoring system according to the first embodiment.

[0020] Figure 3 This is a hardware configuration diagram of the digital protection relay and the digital protection relay monitoring system according to the first embodiment.

[0021] Figure 4 This is a diagram for explaining the usage state of the monitoring device involved in Embodiment 1.

[0022] Figure 5 This is a diagram showing an example of a change over time of the excitation inrush current displayed in the monitoring device according to the first embodiment.

[0023] Figure 6 This is a diagram showing an example of a change over time in the second harmonic content rate of the field inrush current displayed in the monitoring device according to the first embodiment. DETAILED DESCRIPTION

[0024] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same or corresponding parts.

[0025] Implementation method 1.

[0026] Hereinafter, the digital protective relay and the digital protective relay monitoring system according to the first embodiment will be described with reference to the drawings.

[0027] Figure 1 1 is a circuit diagram in which the digital protection relay 1 according to the first embodiment is applied to a transformer 3 for power. Figure 1 In the figure, the transformer 3 as the protected object is connected to the power system power supply (not shown) via the circuit breaker 2 (CB: Circuit Breaker). In addition, a main transformer 4 (CT: Circuit Transformer) is provided to extract the AC current of each phase. The low-voltage side of the transformer 3 is connected to the load (not shown) through the molded case circuit breaker (MCCB: Molded Case Circuit Breaker) 5a, 5b. The AC current extracted by the main transformer 4 is input to the digital protection relay 1. If it is judged to be an overcurrent (fault current) caused by a system fault, the transformer 3 is protected by performing a cut-off action of the circuit breaker 2.

[0028] Figure 2 1 is a functional block diagram of the digital protection relay 1 and the digital protection relay monitoring system 100 according to the first embodiment. Figure 2 In the embodiment, the AC current extracted by the main converter 4 is converted into an appropriate size by the current measuring unit 11. The A / D converter 12 samples the AC current converted by the current measuring unit 11 at a certain time interval and converts it into digital data. The digital data is input to the operation processing unit 13, and a frequency analysis based on digital operations such as FFT (Fast Fourier Transform) or digital addition and subtraction processing is performed. As a result of the frequency analysis, when the ratio of the second harmonic to the fundamental component of the current is greater than the threshold value, it is determined in the control unit 14 as an excitation surge current, and the disconnection action of the circuit breaker 2 is prevented.

[0029] In the threshold learning unit 15, a series of steps for learning are performed from the generation of the excitation impulse current to the threshold calculation. The learned threshold is sent to the control unit 14, and in the control unit 14, it is updated to the threshold of the ratio of the second harmonic to the fundamental component of the current (hereinafter referred to as the second harmonic content rate) used for judging the excitation impulse current. The result of the frequency analysis calculated by the operation processing unit 13 and the learning result of the threshold learning unit 15 are stored and accumulated in the storage unit 16 as a non-volatile memory. In addition, although the details will be described later, the future predicted values ​​of the excitation impulse current and the second harmonic content rate are calculated in the threshold learning unit 15 using the data accumulated in the storage unit 16. The data accumulated in the storage unit 16 is sent to the monitoring device 20 outside the digital protection relay 1 via the communication unit 17. Here, the monitoring device 20 outside the digital protection relay 1 is included in the digital protection relay monitoring system 100.

[0030] Figure 31 is a block diagram showing an example of hardware of the digital protection relay 1 and the digital protection relay monitoring system 100 involved in the first embodiment. The current measuring unit 11 in the digital protection relay 1 is composed of an analog circuit. In addition, the A / D conversion unit 12, the operation processing unit 13, the control unit 14, the threshold learning unit 15, the storage unit 16 and the communication unit 17 are composed of at least a processor 101 and a storage device 102. In addition, the digital protection relay monitoring system 100 is also composed of at least a processor 101 and a storage device 102. Although the storage device 102 is not shown in the figure, it has a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. In addition, an auxiliary storage device such as a hard disk can also be provided instead of the flash memory. The processor 101 executes the program input from the storage device 102, and performs sampling and frequency analysis based on FFT, etc. In this case, the program is input from the auxiliary storage device to the processor 101 via the volatile storage device. In addition, the processor 101 may output data such as the calculation result to the volatile storage device of the storage device 102, or may save the data to 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. In addition, depending on the circuit structure, a structure in which a part of an ASIC (Application Specific Integrated Circuit) is combined in the processor may also be adopted.

[0031] Next, the operations of the threshold learning unit 15 and the monitoring device 20 will be described.

[0032] The main converter 4 always measures the AC current, and the measured AC current is input to the current measuring unit 11. Whenever the circuit breaker 2 is turned on and the transformer 3 is connected to the system, the main converter 4 measures the AC current as the excitation inrush current and inputs it to the current measuring unit 11. The signal converted into an appropriate size by the current measuring unit 11 is converted into digital data in the A / D conversion unit 12. The digital data input to the operation 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 learning unit 15. In addition to the second harmonic content, the excitation inrush current is also input to the threshold learning unit 15. The excitation inrush current and the second harmonic content input to the threshold learning unit 15 are stored in the storage unit 16 together with the time when the data is calculated.

[0033] The threshold learning unit 15 updates the threshold value based on the excitation inrush current and the second harmonic content rate input this time, and sends it to the control unit 14. Furthermore, the excitation inrush current and the second harmonic content rate input this time and the excitation inrush current and the second harmonic content rate stored in the storage unit 16 are used to predict the change over time.

[0034] The data of the excitation inrush current and the second harmonic content rate stored in the storage unit 16 and the temporal changes of the excitation inrush current and the second harmonic content rate predicted by the threshold learning unit 15 are transmitted to the monitoring device 20 via the communication unit 17 .

[0035] Figure 4 2 is a diagram for explaining the use of the monitoring device 20. The monitoring device 20 is a terminal such as a PC (personal computer) or a tablet computer, and the data sent from the digital protection relay 1 is displayed on its display screen. The user of the digital protection relay 1 can monitor the operation status of the digital protection relay 1 based on the displayed information such as the change over time of the excitation inrush current and the second harmonic content rate. In addition, the aging degradation of the transformer 3 and the load can be predicted, and maintenance can be performed before an accident caused by the aging degradation of the transformer 3 and the load occurs. Therefore, the equipment can be operated more stably.

[0036] Next, a method of predicting the temporal change in the ratio of the field inrush current to the second harmonic will be described with reference to the data displayed on the monitoring device 20 .

[0037] Figure 5 and Figure 6 is a diagram showing an example of data displayed on the monitoring device 20, Figure 5 This is an example showing the change of the excitation surge current over time. Figure 6 FIG. 1 is a diagram showing an example of the change in the second harmonic content of the excitation surge current over time. Figure 5 and Figure 6 In the figure, the solid line is the actual data calculated by the digital protection relay 1, and the dotted line is the future predicted value.

[0038] By analyzing the excitation inrush current measured by the digital protection relay 1, the applicant obtained the following information. Due to the degradation of the transformer and the load over the years, the excitation inrush current becomes larger, but the current value of the second harmonic component is a constant value and does not change. In addition, these data change linearly with the passage of time. Therefore, as a change over time, there is a trend that the magnitude of the excitation inrush current increases, but the second harmonic content rate decreases.

[0039] Based on this trend, the simple moving average method is used to calculate future forecast data for the excitation inrush current and the second harmonic content rate from the average values ​​of the actual data.

[0040] The simple moving average method is represented by the following formula, and according to this formula, future prediction data is calculated using the average value of the immediately previous n (n is a natural number greater than or equal to 2) data.

[0041] [Mathematical formula 1]

[0042]

[0043] S t+1 : Prediction value

[0044] Y t :Actual value (latest)

[0045] n: The number of data to be averaged

[0046] When n≤3, a threshold value and a linear function of an initial value pre-set with reference to a transformer of the same model or a load condition connected to a transformer of the same model are used to pre-produce a tentative prediction line graph of changes over time. When n>3, prediction data based on the simple moving average method is generated. At this time, after calculating the (n+1)th prediction data, the (n+2)th prediction data is calculated using the average value of the (n+1) data containing the prediction data, and this operation is repeated to generate a prediction line graph of changes over time.

[0047] When the transformer 3 is connected to the system and new excitation surge current and second harmonic content rate are obtained, the prediction line diagram of the change over time is updated using the new data.

[0048] The user of the digital protection relay 1 can confirm the updated prediction line graph of the excitation surge current and the second harmonic content rate over time through the monitoring device 20 every time the transformer 3 is connected to the system and a new excitation surge current and second harmonic are obtained. In addition, the user can directly set and change the threshold value set in the control unit 14 of the digital protection relay 1 according to the change of the second harmonic content rate over time. The setting function generally provided in the digital protection relay 1 can be used to set the threshold value.

[0049] In addition, the user of the digital protection relay 1 can adjust the threshold value itself or calculate the coefficient of the threshold value to reduce the threshold value according to the operation plan of the transformer 3 and the load connected to the digital protection relay 1, for example, when the transformer 3 and the load are scheduled to be subjected to severe operation that deteriorates, thereby enabling the digital protection relay 1 to be set to operate reliably.

[0050] As described above, the user of the digital protection relay 1 can predict the degradation of the transformer 3 and the load based on the prediction line graph of the excitation inrush current and the second harmonic content rate that has been updated and displayed on the monitoring device 20. If the slope of the prediction line graph increases moment by moment, the maintenance plan can be accelerated, and if the slope of the prediction line graph becomes gentle, the maintenance plan can be modified, and equipment management becomes easy.

[0051] Although the description of the setting and updating method of the threshold value is omitted, the initial value can be updated after using the value predetermined according to the actual situation of the transformer of the same model. Whenever the transformer 3 is connected to the system and a new excitation impulse current and second harmonic content rate are obtained, the obtained second harmonic content rate can be multiplied by a coefficient to set it, or the calculation method disclosed in International Publication No. 2019 / 043910 can be used.

[0052] In addition, whenever the circuit breaker 2 is turned on and the transformer 3 is connected to the system, the AC current is measured as the excitation surge current, and the threshold value is calculated by the threshold learning unit 15 and sent to the control unit 14. The data is continuously accumulated in the storage unit 16. However, regarding the trigger for turning on the circuit breaker 2 and connecting the transformer 3 to the system, the trigger is used when the digital protective relay 1 itself generates an action signal for the circuit breaker 2.

[0053] As described above, according to the first embodiment, the digital protection relay 1 of the present embodiment calculates the second harmonic content rate by the operation processing unit 13 based on the input excitation inrush current, calculates the threshold value by the threshold learning unit 15, and updates the threshold value of the control unit 14, so that the threshold value accompanying the change over time can be set. In addition, the excitation inrush current and the second harmonic content rate are stored and accumulated in the storage unit 16 together with the time when these are calculated, and the threshold learning unit 15 predicts and calculates the future change over time based on the accumulated data and the newly calculated excitation inrush current and the second harmonic content rate. The monitoring device 20 outside the digital protection relay 1 acquires and displays the data accumulated in the storage unit 16 and the change over time including the future predicted value calculated by the threshold learning unit 15, so that the user of the digital protection relay 1 can confirm the visualized data and directly input the change of the threshold value to the digital protection relay 1.

[0054] In addition, the digital protection relay monitoring system 100 according to the present embodiment provides the user with data of the excitation inrush current and the second harmonic content rate accumulated in the digital protection relay 1 and their future predicted values ​​in a visualized manner, and can monitor not only the digital protection relay 1 but also the degradation state of the equipment such as the transformer 3 connected to the digital protection relay. Furthermore, the maintenance of the equipment can be reasonably planned based on the degradation state of the equipment.

[0055] The present disclosure describes various exemplary embodiments and examples, but various features, forms, and functions described in one or more embodiments are not limited to application in specific embodiments and can be applied to the embodiments alone or in various combinations.

[0056] Therefore, it is considered that numerous modifications not shown in the examples are also included in the technical scope disclosed in the present specification, for example, including the case where at least one component is modified, added or omitted, and the case where at least one component is extracted and combined with components of other embodiments.

[0057] Description of symbols

[0058] 1: digital protection relay, 2: circuit breaker, 3: transformer, 4: main converter, 5a, 5b: fuseless circuit breaker, 11: current measuring unit, 12: A / D conversion unit, 13: operation processing unit, 14: control unit, 15: threshold learning unit, 16: storage unit, 17: communication unit, 20: monitoring device, 100: digital protection relay monitoring system, 101: processor, 102: storage device.

Claims

1. A digital protection relay, which inputs an alternating current flowing through a transformer and performs a disconnection action of a circuit breaker connected to the transformer when an overcurrent is detected, characterized in that: include: an A / D conversion unit, the A / D conversion unit sampling the input alternating current at a certain time interval; an operation processing unit that performs frequency analysis based on the digital value sampled by the A / D conversion unit; a control unit that, when a ratio of the second harmonic extracted by the arithmetic processing unit contained in the excitation inrush current is equal to or greater than a predetermined threshold, blocks a disconnection operation of the circuit breaker; a threshold learning unit that updates the threshold value according to the ratio of the second harmonic extracted by the calculation processing unit contained in the excitation surge current every time the circuit breaker is turned on and the transformer is connected; as well as a storage unit that stores the excitation inrush current and the ratio of the second harmonic contained in the excitation inrush current used for threshold value updating in the threshold value learning unit together with the time when the excitation inrush current and the second harmonic are calculated, The threshold learning unit calculates the temporal changes of the excitation impulse current and the ratio of the second harmonic contained in the excitation impulse current including future predicted values ​​based on the excitation impulse current and the ratio of the second harmonic contained in the excitation impulse current stored in the storage unit, and the excitation impulse current newly input when the circuit breaker is turned on and the transformer is connected and the ratio of the second harmonic contained in the excitation impulse current extracted by the calculation processing unit.

2. The digital protection relay according to claim 1, characterized in that: In the threshold learning unit, a simple moving average method is used to calculate changes over time in the excitation inrush current including a future predicted value and in the ratio of the second harmonic included in the excitation inrush current.

3. The digital protection relay according to claim 1 or 2, characterized in that: The threshold learning unit calculates and updates the temporal changes of the excitation inrush current and the proportion of the second harmonic contained in the excitation inrush current including future predicted values ​​based on the excitation inrush current newly input each time the circuit breaker is turned on and the transformer is connected and the proportion of the second harmonic contained in the excitation inrush current extracted by the calculation processing unit.

4. A digital protection relay monitoring system, characterized in that: include: The digital protection relay according to any one of claims 1 to 3; as well as a monitoring device connected to the digital protection relay, The monitoring device displays changes over time in the excitation inrush current including a future predicted value calculated by the threshold learning unit of the digital protective relay and in the ratio of the second harmonic included in the excitation inrush current.

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