JP7792865B2 - Digital protection relay and its maintenance management system - Google Patents

Description

This disclosure relates to a digital protective relay and its maintenance management system.

To ensure high reliability of protective relays, the hardware is equipped with a continuous monitoring function that detects faults through self-diagnosis. Calculations for continuous monitoring are performed during the relay calculation process gap time within the relay calculation cycle.

Specifically, as described in paragraph [0002] of Japanese Patent Application Laid-Open No. 2008-118747 (Patent Document 1), when an abnormality is confirmed according to the abnormality detection conditions defined for each monitoring item, an external alarm is output. The output external alarm is notified to a maintenance base via a remote monitoring control panel or the like. When maintenance personnel at the maintenance base receive an external alarm, they rush to the digital protective relay device where the abnormality occurred, even if it is on a holiday or at night, and they confirm the nature of the abnormality and then carry out recovery measures.

Once a fault occurs, as described above, an emergency investigation into the cause and recovery work are required, so measures are needed to prevent excessive fault detection. For this reason, some digital protective relay inspection items are set to only report an abnormality if fault symptoms continue for a certain period of time (for example, Table 2.14 in Non-Patent Document 1). The duration can be set to, for example, 10 seconds, 15 seconds, 20 seconds, 60 seconds, etc.

JP 2008-118747 A

"Protection Relay System Basic Technology System," edited by the Basic Technology Research Committee for Protection Relay Systems, Institute of Electrical Engineers of Japan Technical Report No. 641, July 1997

In the case of a transient fault where the duration of the malfunction symptoms is less than the set time and the symptoms disappear quickly, not only will no external alarm be output, but the fault will not be recorded. For this reason, conventional continuous monitoring functions are essentially for post-event maintenance and are not intended for preventative maintenance.

Patent Document 1 above proposes a preventive maintenance method in which a judgment value is set that can be used to determine that a device component has deteriorated, even if it does not meet the threshold for the abnormality detection condition, and maintenance information is notified when the component reaches the judgment value. However, once deterioration of a component occurs, the threshold for the abnormality detection condition is often exceeded, and it is not easy to set appropriate deterioration judgment conditions between normal and abnormal states.

This disclosure has been made in consideration of the above-mentioned problems, and one of its objectives is to provide a digital protective relay with a constant monitoring function that enables preventive maintenance.

In one embodiment, the digital protective relay comprises an input conversion unit, an analog input unit, and an arithmetic processing unit. The input conversion unit performs level conversion on the measured values of electrical quantities in the power system input via multiple channels. The analog input unit performs digital conversion on the measured values of electrical quantities level-converted by the input conversion unit. The arithmetic processing unit performs protective relay calculations using the digitally converted measured values of electrical quantities. The arithmetic processing unit performs continuous monitoring processing on at least the input conversion unit and the analog input unit during idle time between protective relay calculations. During the continuous monitoring processing, if an abnormality determination condition is met, in which a determination value calculated using the digitally converted measured values of electrical quantities exceeds a threshold, the arithmetic processing unit determines that the input conversion unit or the analog input unit has failed, and if the duration of the abnormality determination condition does not reach the specified time, records information indicating the degree of deterioration of the input conversion unit or the analog input unit.

According to the above embodiment, if the duration of the abnormality determination condition during continuous monitoring processing does not reach the specified time, preventive maintenance is possible by recording information indicating the degree of deterioration of the input conversion unit or analog input unit being monitored.

FIG. 1 is a block diagram showing an example of the configuration of a digital protection relay. FIG. 10 is a diagram showing examples of continuous monitoring items in a table format. 1 is a flowchart showing a continuous monitoring procedure in the digital protection relay of the first embodiment. 10A and 10B are diagrams conceptually showing an example of a change in a determination value over time and a failure determination result based on the change in a determination value; 10 is a flowchart showing a continuous monitoring procedure in the protection relay device of embodiment 2. FIG. 6 is a diagram showing an example of data stored in step S70A of FIG. 5 in the case of zero-phase monitoring. 11 is a flowchart for explaining a monitoring procedure that is periodically executed in the digital protection relay of the third embodiment. FIG. 2 is a diagram showing, in a table format, information stored in a nonvolatile memory of the arithmetic processing unit. FIG. 9 is a graph showing the information in FIG. 8.

Each embodiment will be described in detail below with reference to the drawings. Note that identical or corresponding parts will be given the same reference symbols and their descriptions will not be repeated.

Embodiment 1.
[Outline of digital protection relay]
Fig. 1 is a block diagram showing an example of the configuration of a digital protective relay. Referring to Fig. 1, the digital protective relay 100 includes an input conversion unit 10, an analog input unit 20, an arithmetic processing unit 30, an IO (Input and Output) unit 40, a bus 50, a power supply unit 51, a power supply monitoring unit 52, and a communication unit 53. The configuration and operation of each element will be briefly described below.

The input conversion unit 10 includes input converters 11 (11A, 11B) provided for each of the multiple channels. Figure 1 shows only two representative channels.

Each input converter 11 converts a voltage signal detected by a voltage transformer (VT) 2 installed on the power line 1 or a current signal detected by a current transformer (CT) 3 installed on the power line 1 into a signal level suitable for signal processing within the digital protection relay 100. For example, an auxiliary transformer (auxiliary voltage transformer, auxiliary current transformer) is used as the input converter 11.

Note that although power line 1 is configured as a three-phase AC power line (i.e., a transmission line or distribution line), it is shown as a single line in Figure 1 for ease of illustration. Therefore, a voltage transformer 2 and a current transformer 3 are actually provided for each phase, and correspondingly, three channels of input converter 11 are also provided for each phase.

The analog input unit 20 includes an analog filter 21 (21A, 21B) provided for each channel, a sample and hold circuit (S/H) 22 (22A, 22B) provided for each channel, a multiplexer (MUX) 23, an analog-to-digital converter (ADC) 24, and a reference voltage source 25.

The analog filter 21 is provided to avoid aliasing errors caused by sampling in the analog-to-digital converter 24. Ideally, the analog filter 21 may be a low-pass filter that attenuates at least half the sampling frequency, but in practice, it may be a filter that provides significant attenuation between the rated frequency of the power system and the sampling frequency.

The sample-and-hold circuit 22 samples and holds the voltage signal or current signal for each channel. The sample-and-hold circuit 22 is not necessarily provided. The multiplexer 23 sequentially selects the values held in the sample-and-hold circuit 22 for each channel. The analog-to-digital converter 24 performs AD conversion on the values selected by the multiplexer 23.

The arithmetic processing unit 30 includes a central processing unit (CPU) 31 and memory 32. The memory 32 includes ROM (Read Only Memory) and RAM (Random Access Memory) used as main memory, as well as electrically rewritable non-volatile memory used as auxiliary memory.

The calculation processing unit 30 executes relay calculation processing and also executes continuous monitoring processing during idle time in the relay calculation processing. These functions of the calculation processing unit 30 are realized by the central processing unit 31 executing programs stored in memory 32.

The IO section 40 includes multiple digital output circuits (D/O: Digital Output) 41 and multiple digital input circuits (D/I: Digital Input) 42. In Figure 1, one digital output circuit 41 and one digital input circuit 42 are shown as representative examples.

The digital output circuit 41 outputs a digital signal (i.e., a logical value having a high level and a low level) to the outside of the digital protection relay 100. For example, the digital output circuit 41 outputs a trip signal to a trip circuit 43 that opens a circuit breaker (CB) 4 installed on the power line 1. The calculation processing unit 30 can detect an open circuit in the trip circuit 43 via the bus 50 and the digital output circuit 41.

The digital input circuit 42 receives digital signals (i.e., logic values having high and low levels) from outside the digital protection relay 100. For example, the digital input circuit 42 receives contact information representing the open/closed state of the circuit breaker 4 and switch (not shown) installed on the power line 1.

The power supply unit 51 supplies power to each component of the digital protection relay 100. The power supply monitoring unit 52 monitors whether the voltage and current output from the power supply unit 51 are within specified ranges.

The communication device 53 exchanges information with a monitoring server 54 installed at the maintenance base. For example, the calculation processing unit 30 outputs the results of continuous monitoring processing to the monitoring server 54 via the communication device 53. A maintenance management system is constructed by the digital protection relay 100 and the monitoring server 54.

[Overview of continuous monitoring function]
The calculation processing unit 30 constantly monitors the entire digital protection relay 100, from the input unit to the output unit, in hardware block units. The constant monitoring calculation is performed during the relay calculation cycle, utilizing the idle time other than the relay calculation. For example, if the rated frequency of the power system is 50 Hz and the relay calculation is performed every 30 electrical degrees, the relay calculation cycle is approximately 1.67 milliseconds. Therefore, the constant monitoring cycle is also approximately 1.67 milliseconds.

Figure 2 shows an example of items that are continuously monitored in table format. The table in Figure 2 is based on, for example, Table 2.14 in Non-Patent Document 1 ("Protection Relay System Basic Technology System," Institute of Electrical Engineers Technical Report No. 641, July 1997). In the example of items that are continuously monitored shown in Figure 2, the calculation processing unit 30 determines that an abnormality has occurred if the abnormality detection conditions continue for a certain period of time.

Specifically, in negative-phase sequence monitoring, the calculation processing unit 30 takes in the three-phase voltage and three-phase current of the power system as measured values and calculates the magnitude of the negative-phase sequence voltage and current using the symmetric coordinate method as judgment values. The calculation processing unit 30 determines whether the abnormality judgment condition, in which the magnitude of the negative-phase sequence voltage and current calculated as judgment values exceeds a threshold value, continues for a certain period of time.

In zero-phase monitoring, the calculation processing unit 30 takes in the three-phase voltage and three-phase current of the power system as measured values and calculates the magnitude of the zero-phase voltage and zero-phase current using the symmetric coordinate method as judgment values. The calculation processing unit 30 determines whether the magnitude of the zero-phase voltage and zero-phase current calculated as judgment values exceeds a threshold value, which is an abnormality judgment condition, continues for a certain period of time.

To check the accuracy of the AD conversion, the calculation processing unit 30 selects the output voltage of the reference voltage source 25 using the multiplexer 23 and takes in the value AD converted by the analog-to-digital converter 24 as the measurement value. The calculation processing unit 30 calculates the error between the AD converted value of the output voltage of the reference voltage source 25 and the expected value as a judgment value. The calculation processing unit 30 determines whether the abnormality judgment condition, in which the magnitude of the AD conversion error calculated as the judgment value exceeds a threshold value, continues for a certain period of time.

When monitoring D/I inputs, the arithmetic processing unit 30 detects information about the open/closed state of the same contact (circuit breaker, switch) via different digital input circuits 42. The arithmetic processing unit 30 determines whether the abnormality determination condition, that the contact information of the detected same contact does not match, continues for a certain period of time.

When monitoring the D/O output, the arithmetic processing unit 30 detects the results of the opening and closing commands output via the digital output circuit 41 using the digital input circuit 42. The arithmetic processing unit 30 determines whether the abnormality determination condition, that is, a mismatch between the output opening and closing command and its result, continues for a certain period of time.

When monitoring the trip circuit, the calculation processing unit 30 determines whether a disconnection state (abnormality determination condition) in which a current sufficiently smaller than the minimum operating current flows through the trip coil and the current becomes high resistance and cannot be detected continues for a certain period of time.

Power supply monitoring determines whether the abnormality determination condition, in which the error between the measured output voltage of the power supply device 51 and the expected value exceeds a threshold, continues for a certain period of time.

In this way, with the continuous monitoring function described above, the calculation processing unit 30 measures electrical quantities or logical values related to the monitored object and determines whether the abnormality determination conditions based on the measured electrical quantities or logical values have continued for a certain period of time. If the abnormality determination conditions have continued for a certain period of time, the calculation processing unit 30 determines that the monitored component or unit has failed.

[Deterioration detection function]
Next, a preventive maintenance method for detecting the degree of deterioration of a monitored part or unit before it reaches a breakdown will be described.

Figure 3 is a flowchart showing the continuous monitoring procedure for the digital protective relay of embodiment 1. The continuous monitoring function is executed during idle time in the protective relay calculations at each calculation cycle of the protective relay calculations.

In step S10, the calculation processing unit 30 in FIG. 1 measures an electrical quantity (i.e., voltage or current) or logical value related to the unit being monitored and captures the measurement value. For example, in the case of negative-phase sequence monitoring and zero-phase sequence monitoring in FIG. 2, the three-phase voltage or three-phase current of the power system is captured as the measurement value, and in the case of an AD conversion accuracy check, the output voltage of the reference voltage source 25 is captured as the measurement value. In the case of D/I input monitoring and D/O output monitoring, a logical value of "1" or "0" is captured as the measurement value via the digital input circuit 42. In the case of trip circuit monitoring, the current flowing through the trip coil being monitored is captured as the measurement value, and in the case of power supply monitoring, the output voltage of the power supply unit 51 is captured as the measurement value.

In the next step S20, the calculation processing unit 30 calculates a judgment value based on the acquired measured values. For example, in the case of negative-phase sequence monitoring in FIG. 2, the magnitude of the negative-phase sequence voltage and negative-phase sequence current is calculated as the judgment value, and in the case of zero-phase sequence monitoring, the magnitude of the zero-phase sequence voltage and zero-phase sequence current is calculated as the judgment value. In the case of an A/D conversion accuracy check, the magnitude of the error between the measured value and the expected value is calculated as the judgment value. In the case of D/I input monitoring, the difference between the logical values acquired via the different first and second digital input circuits 42 is calculated as the judgment value. In the case of D/O output monitoring, the difference between the logical value output via the digital output circuit 41 and the logical value acquired via the digital input circuit 42 is calculated as the judgment value. In the case of trip circuit monitoring, the measured current value is used as the judgment value. In the case of power supply monitoring, the magnitude of the error between the measured value and the expected value is calculated as the judgment value.

In the next step S30, the calculation processing unit 30 determines whether the judgment value calculated in step S20 exceeds the threshold value, i.e., whether the abnormality judgment condition is met. If the judgment value is equal to or less than the threshold value, i.e., if the abnormality judgment condition is not met (NO in step S30), the calculation processing unit 30 ends the continuous monitoring process.

On the other hand, if the judgment value exceeds the threshold value (YES in step S30), in the next step S40, the calculation processing unit 30 determines whether the state in which the judgment value exceeds the threshold value continues for a certain period of time, i.e., whether the state in which the abnormality judgment condition is satisfied continues for a certain period of time. In the case of Figure 3, a specified time of, for example, 20 seconds is selected as the certain period of time.

If the determination value exceeds the threshold for a certain period of time (YES in step S40), in step S50, the calculation processing unit 30 determines that the monitored unit is faulty and stores fault information, such as the monitored item determined to be faulty and the date and time the fault occurred, in non-volatile memory. Furthermore, in the next step S60, the calculation processing unit 30 outputs an alarm external to the digital protection relay 100. Specifically, the calculation processing unit 30 notifies the monitoring control panel or the like of the alarm via the digital output circuit 41. Furthermore, the monitoring control panel or the like notifies the maintenance base of an abnormality alarm.

On the other hand, if the state in which the judgment value exceeds the threshold value does not continue for a certain period of time (NO in step S40), in step S70, the calculation processing unit 30 records the duration of the abnormality judgment condition in non-volatile memory as information representing the deterioration state of the monitored object, along with information such as the monitored item and date and time.

In the next step S80, the calculation processing unit 30 transmits the information stored in the non-volatile memory to the monitoring server 54 installed at the maintenance base. This completes the continuous monitoring procedure.

Figure 4 is a conceptual diagram showing an example of how the judgment value changes over time and the fault judgment result based on that change. Referring to Figure 4, let's assume that the judgment value exceeds the threshold value TH at time t1. At this point, the fault judgment result is low (L) level, and a fault has not yet been confirmed.

At time t2, the judgment value remains above the threshold value TH for a specified time (20 seconds in this case). As a result, the fault judgment result becomes high (H), confirming the fault.

On the other hand, if the judgment value returns to below the threshold value (TH) at time t3 (19 seconds have passed since time t1), before time t2 is reached, a fault is not confirmed. In this case, the calculation processing unit 30 records the duration of the state in which the judgment value exceeded the threshold value TH as information for preventive maintenance indicating the deterioration state of the monitored object.

[Effects of First Embodiment]
According to the continuous monitoring procedure described above, even if the condition for determining an abnormality is not met for the specified time and a failure is not determined, information indicating the deterioration state of the monitored object is recorded. Therefore, the progress of deterioration of a part can be identified and the degree of deterioration can be diagnosed. For example, the monitoring server 54 at the maintenance base may predict the replacement time of a part based on the accumulated records of the duration of multiple abnormalities. This prediction may be performed using artificial intelligence (AI). This enables preventive maintenance before a failure of the equipment is confirmed, preventing unexpected part replacement and enabling planned equipment upgrades.

Furthermore, compared to the aforementioned Patent Document 1 (JP 2008-118747 A), this embodiment has the advantage of not requiring the use of a criterion for determining deterioration in addition to a threshold value for determining a failure. This is because setting such a criterion is practically difficult.

In the above, the fault information or preventive maintenance information stored in the non-volatile memory is transmitted to the monitoring server 54 installed at the maintenance base, but transmitting the information is not necessarily required. For example, a maintenance technician at the maintenance base may periodically visit the location where the digital protection relay 100 is installed and retrieve the information from the non-volatile memory, or the owner of the digital protection relay 100 may periodically retrieve the information from the non-volatile memory.

Furthermore, for monitoring items that utilize electrical quantities (voltage and current) from the power system (for example, negative-phase and zero-phase monitoring in Figure 2), the measured values also include influences from the power system (flicker, equipment harmonics, voltage fluctuations, frequency fluctuations, etc.). Therefore, not only can the deterioration of digital protective relays be diagnosed, but unnecessary alarms or relay malfunctions caused by the power system can also be prevented.

Embodiment 2.
In the second embodiment, the information indicating the degree of deterioration of the monitored object that is recorded when the state in which the abnormality determination condition is satisfied does not continue for a specified time and a failure is not determined is different from that in the first embodiment. A specific description will be given below with reference to the drawings.

Figure 5 is a flowchart showing the continuous monitoring procedure in the protective relay device of embodiment 2. The continuous monitoring procedure in Figure 5 differs from the flowchart in Figure 3 in that step S70A is provided instead of step S70.

Specifically, if the state in which the abnormality determination condition is satisfied does not continue for a specified time (20 seconds in the case of Figure 5) (NO in step S40), the calculation processing unit 30 proceeds to step S70A. In step S70A, the calculation processing unit 30 records the determination value data within the specified time after the determination value exceeds the threshold (i.e., after the abnormality determination condition is satisfied) in non-volatile memory along with the monitored item and date and time. Here, since recording the determination value every continuous monitoring cycle (e.g., 1.67 milliseconds) would result in too much recorded data, the calculation processing unit 30 records the determination value data by thinning it out, for example, every second. As Figure 5 is otherwise similar to Figure 3, the same or corresponding steps are designated with the same reference numerals and descriptions will not be repeated.

Figure 6 shows an example of the data stored in step S70A of Figure 5 in the case of zero-phase monitoring. The judgment value (zero-phase current) exceeds the threshold value of 0.2 A for only the first 5 seconds of the specified 20-second time period. For the remaining 15 seconds, the judgment value does not exceed the threshold. In Figure 6, the judgment value data is recorded at 1-second intervals.

As described above, with the continuous monitoring of the protective relay device of embodiment 2, as in embodiment 1, even if the abnormality determination conditions are not met for the specified time and a failure is not determined, information indicating the deterioration state of the monitored object is recorded. Therefore, it is possible to grasp the progression of deterioration of a component and diagnose the degree of deterioration.

In particular, in the case of embodiment 1, only the duration of the state in which the judgment value exceeded the threshold was recorded, so in order to diagnose the degree of deterioration of the monitored object, it was necessary to repeatedly collect a large amount of information. On the other hand, in embodiment 2, a single piece of information includes the change in the judgment value over time within a specified period of time. Therefore, the degree of deterioration can be diagnosed based on multiple pieces of information obtained over a shorter period of time than in embodiment 1.

Note that embodiment 1 and embodiment 2 may be combined and implemented. That is, if the state in which the abnormality determination condition is satisfied does not continue for a specified time, the calculation processing unit 30 records information representing the degree of deterioration of the monitored object. Here, the information representing the degree of deterioration may be the duration of the abnormality determination condition, or multiple measurement values or multiple determination values for the monitored object obtained within a specified time after the abnormality determination condition is satisfied, or both.

Embodiment 3.
In the digital protective relay of the third embodiment, even if the judgment value does not exceed the threshold, the measured value or judgment value of the electrical quantity related to the monitored object is recorded at predetermined intervals. The monitoring procedure of the third embodiment is executed in combination with the continuous monitoring procedures of the first and second embodiments. The following is a specific description with reference to the drawings.

Figure 7 is a flowchart illustrating the monitoring procedure that is periodically performed in the digital protection relay of embodiment 3.

In step S100, the calculation processing unit 30 determines whether it is a regular measurement date for the monitored object. The measurement date is determined based on the standard lifespan of the monitored object, such as once a year.

If it is a regular measurement day for the monitored object (YES in step S100), in step S110, the calculation processing unit 30 measures an electrical quantity (i.e., voltage or current) or logical value related to the monitored object and captures the measurement value. In the next step S120, the calculation processing unit 30 calculates a judgment value based on the captured measurement value. Here, steps S110 and S120 are the same as steps S10 and S20 in Figures 3 and 5. In other words, the monitoring procedure in Figure 7 is executed in combination with the continuous monitoring procedure in Figures 3 and 5.

In the next step S130, the calculation processing unit 30 stores the measurement value or judgment value along with the monitoring item and measurement date in non-volatile memory. In the next step S140, the calculation processing unit 30 transmits the information stored in non-volatile memory to the monitoring server 54 installed at the maintenance base.

In the next step S150, the monitoring server 54 at the maintenance base outputs the changes over time in the measurement values or judgment values of the monitored objects that it periodically receives. The monitoring server 54 can identify the progression of deterioration of the parts based on the changes over time in the measurement values or judgment values, and diagnose the degree of deterioration.

Figure 8 is a table showing the information stored in the non-volatile memory of the calculation processing unit. The non-volatile memory stores the monitoring item, measurement date, and judgment value (zero-phase current).

Figure 9 is a graph showing the information in Figure 8. In this way, by periodically capturing the measured or judged values of the monitored object and displaying them as changes over time, it is possible to determine the degree of deterioration over time even if the judged value has not reached the threshold value.

The embodiments disclosed herein should be considered in all respects as illustrative and not restrictive. The scope of this application is indicated by the claims, not the above description, and all modifications within the meaning and scope of the claims are intended to be included.

Various aspects of the present disclosure are summarized below as appendices.
(Appendix 1)
an input conversion unit that converts the levels of measured values of electrical quantities of the power system input via a plurality of channels;
an analog input unit that digitally converts the measured value of the electrical quantity that has been level-converted by the input conversion unit;
a calculation processing unit that performs a protective relay calculation using the measured value of the electric quantity converted into digital data,
the calculation processing unit performs a constant monitoring process on at least the input conversion unit and the analog input unit during a time when the protection relay calculation is not performed,
The calculation processing unit determines that the input conversion unit or the analog input unit has failed if an abnormality determination condition, in which a determination value calculated using the measurement value of the digitally converted electrical quantity exceeds a threshold, continues for a specified time during the continuous monitoring process, and records information representing the degree of deterioration of the input conversion unit or the analog input unit if the duration of the abnormality determination condition does not reach the specified time.
(Appendix 2)
2. The digital protective relay according to claim 1, wherein the information representing the degree of deterioration includes a duration of the abnormality determination condition.
(Appendix 3)
3. The digital protective relay according to claim 1, wherein the information representing the degree of deterioration includes a plurality of the judgment values obtained between the satisfaction of the abnormality judgment condition and the elapse of the specified time.
(Appendix 4)
The digital protective relay according to any one of appendices 1 to 3, wherein the calculation processing unit periodically records the judgment value as information representing the degree of deterioration regardless of whether the judgment value has reached the threshold value.
(Appendix 5)
The digital protection relay according to any one of appendices 1 to 4, further comprising a communication device for transmitting information representing the degree of deterioration.
(Appendix 6)
a digital protective relay according to appendix 5;
A maintenance management system for digital protection relays, comprising: a monitoring server provided at a maintenance base and configured to receive information indicating the degree of deterioration from the digital protection relays.

1 Power line, 2 Voltage transformer, 3 Current transformer, 4 Circuit breaker, 10 Input conversion unit, 11 Input converter, 20 Analog input unit, 21 Analog filter, 22 Sample and hold circuit, 23 Multiplexer, 24 Analog-to-digital converter, 25 Reference voltage source, 30 Processing unit, 31 Central processing unit, 32 Memory, 40 Unit, 41 Digital output circuit, 42 Digital input circuit, 43 Trip circuit, 50 Bus, 51 Power supply unit, 52 Power supply monitoring unit, 53 Communication unit, 54 Monitoring server, 100 Digital protection relay.

Claims (6)

an input conversion unit that converts the levels of measured values of electrical quantities of the power system input via a plurality of channels;
an analog input unit that digitally converts the measured value of the electrical quantity that has been level-converted by the input conversion unit;
a calculation processing unit that performs a protective relay calculation using the measured value of the electric quantity converted into digital data,
the calculation processing unit performs a constant monitoring process on at least the input conversion unit and the analog input unit during a time when the protection relay calculation is not performed,
The calculation processing unit determines that the input conversion unit or the analog input unit has failed if an abnormality determination condition, in which a determination value calculated using the measurement value of the digitally converted electrical quantity exceeds a threshold, continues for a specified time during the continuous monitoring process, and records information indicating the degree of deterioration of the input conversion unit or the analog input unit as a transient failure without erasing it, for preventive maintenance purposes to determine the progression of component deterioration if the duration of the abnormality determination condition does not reach the specified time. The digital protective relay according to claim 1 , wherein the information representing the degree of deterioration is a duration of the abnormality determination condition. The digital protective relay according to claim 1 , wherein the information representing the degree of deterioration is a plurality of the judgment values obtained during the period from when the abnormality judgment condition is satisfied until when the specified time has elapsed. The digital protective relay described in claim 1, wherein the calculation processing unit periodically records the judgment value as information representing the degree of deterioration, regardless of whether the judgment value has reached the threshold value. The digital protective relay described in any one of claims 1 to 4 further comprises a communication device for transmitting information indicating the degree of deterioration. The digital protection relay according to claim 5;
A maintenance management system for digital protection relays, comprising: a monitoring server provided at a maintenance base and configured to receive information indicating the degree of deterioration from the digital protection relays.