JP2003348746A - Digital protective relay - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a digital protective relay that resets a monitoring timer in a monitoring circuit, when it detects a monitored defect signal generated through a cause other than an analog input circuit, so that unwanted monitored defect signals are not output from the monitoring circuit. <P>SOLUTION: A DC voltage monitoring signal, generated by a monitoring signal generator 5, is overlapped over electrical variables input from a system 2. The composited signal undergoes A/D conversion by an analog input circuit 7 into a digital signal 8, from which a monitoring digital signal 10 and an input electrical variable digital signal 11 are discriminated by a pulse shape discriminating circuit 9. The monitoring digital signal 10 is monitored by a monitoring circuit 12 to monitor abnormalities in the analog input circuit 7, and the polarity of the monitoring digital signal 10 is monitored by a monitoring control circuit 14; when inversion of the polarity is detected, the monitored defect signal 13 is not output by the monitoring circuit 12. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sampling type digital protection relay for inputting an electric quantity of an electric power system through an analog input circuit and protecting the electric power system using the same, and more particularly to detecting a failure of the analog input circuit. The present invention relates to a digital protection relay provided with a monitoring device for performing the operation.

[0002]

2. Description of the Related Art There are various types of conventional protection relays for protecting a power system, but recently, there are many so-called digital protection relays for protecting a power system using a digital processing unit such as a microcomputer. Has been adopted. This digital type protection relay converts an electric quantity input from a system to an analog input circuit at a predetermined sampling frequency, and then takes the digital signal into an arithmetic processing unit to perform arithmetic processing necessary for power system protection. I do. Since this type of technique is already known, a detailed description thereof will be omitted here.

[0003] Such a digital protection relay has conventionally been provided with a monitoring circuit for detecting the presence or absence of a defect in an analog input circuit as disclosed in Japanese Patent Application Laid-Open No. 02-285920. This monitoring circuit superimposes a DC monitoring signal on a digital signal obtained by A / D conversion of an electric quantity input to an analog input circuit, and further detects a change in the monitoring signal, thereby obtaining an analog input signal. Is detected. FIG. 5 is a flowchart showing a monitoring control flow of a conventional digital protection relay.

Next, a monitoring control flow of the digital protection relay will be described with reference to FIG. Step S1
Then, the effective value of the digital signal of the monitoring signal is calculated and obtained. In step S2, it is determined whether the calculated effective value is within a predetermined range, and if it is within the predetermined range, the monitoring timer is reset in step S3. If it is not within the predetermined range, the monitoring timer is added in step S4. After step S3 or step S4 ends, step S5
Then, it is determined whether or not the monitoring timer has exceeded a predetermined time. If not, the process is terminated. If so, the monitoring failure is determined and a monitoring failure signal is output in step S6. And finish. In this way, a fault in the analog input has been detected.

[0005]

However, in the above-described conventional monitoring circuit, when the frequency of the electric quantity input to the analog input circuit fluctuates, the fluctuation of this frequency is discriminated by a waveform discrimination circuit described later. In some cases, the protection signal may be affected, and the protection system may be unnecessarily locked by determining that the analog input circuit is defective even though the analog input circuit has no defect. For this reason, there was a possibility that the operation rate of the protection relay would decrease.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and when a monitoring failure signal generated by a factor other than the analog input circuit is detected, the monitoring timer of the monitoring circuit is reset and the monitoring circuit is reset. It is an object of the present invention to obtain a digital protection relay in which an unnecessary monitoring failure signal is not output from the digital protection relay.

[0007]

SUMMARY OF THE INVENTION In a digital protection relay according to the present invention, a digital protection relay for performing A / D conversion of an electric quantity having a fundamental frequency inputted from a power system and performing protection operation processing of the power system. In relays,
A monitoring signal generator for generating a monitoring signal of a predetermined DC voltage, a superimposing circuit for superimposing a monitoring signal generated by the monitoring signal generator on an electric quantity input from a power system, and a superimposing circuit Input circuit for A / D-converting the superimposed composite signal at a predetermined sampling frequency, and discriminates a monitoring signal component and an electric quantity component from a digital signal formed by A / D conversion by the analog input circuit. A monitoring circuit for monitoring the abnormality of the analog input circuit based on whether the monitoring signal component distinguished by the distinguishing circuit is within the monitoring level range,
A monitoring circuit that outputs a monitoring failure signal when an abnormality is detected, and a monitoring control circuit that monitors the polarity of the monitoring signal component, and when the monitoring control circuit detects a reversal of the polarity of the monitoring signal component. , So that the monitoring failure signal is not output by the monitoring circuit.

The monitoring of the polarity of the monitoring signal component by the monitoring control circuit is performed in synchronization with the sampling frequency.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a digital protection relay according to Embodiment 1 of the present invention. In FIG. 1, 1 is a digital protection relay, 2 is a system, 3 is an instrument current transformer provided in the system 2, 4 is an instrument transformer 4 provided in the system 2,
The amount of current and voltage having a fundamental frequency is input to the digital protection relay 1 via an instrument current transformer 3 and an instrument transformer 4 provided in the system 2. 5 is a monitoring signal generator for generating a monitoring signal of a predetermined DC voltage,
Reference numeral 6 denotes a superimposing circuit for superimposing a monitoring signal of a predetermined DC voltage generated by the monitoring signal generator 5 on an input electric quantity from the system 2, and 7 denotes an analog to which a composite signal superimposed by the superimposing circuit 6 is input. An input circuit 8 is a digital signal converted by an analog input signal 7, 9 is a digital signal 8, which is input to a digital signal 10 (monitoring signal component) of a monitoring signal and an input from the system 2. A waveform discriminating circuit (discriminating circuit) for discriminating the digital signal 11 (electric component) from the electric quantity, and a monitoring signal digital signal 10 discriminated by the waveform discriminating circuit 9 is input to the waveform discriminating circuit 12. Is detected, the monitoring failure signal 13 is detected.
A monitoring circuit for outputting a signal to an alarm circuit;
The digital signal 10 of the monitoring signal discriminated by the above is input, a predetermined DC voltage generated by the monitoring signal generator 5 is measured, and when the DC voltage is out of an allowable range for a predetermined time, a lock signal is generated. Monitoring control circuit to output,
Reference numeral 15 denotes a relay operation circuit to which the input electric quantity digital signal 11 discriminated by the waveform discrimination circuit 9 is input.
1 performs an arithmetic process necessary for system protection, inputs the protection output to a logic circuit 16 including an inhibit circuit, and inputs a signal output from the monitoring circuit 12 to a negative input terminal of the logic circuit 16 for monitoring. When a failure signal is output, the protection output signal to the trip circuit is locked. 5 to 7, 9, 12, 14, 15, and 16 constitute the digital relay 1. The monitoring circuit 12
The monitoring control circuit 14 is configured by software. Here, the analog input circuit 7 includes an analog filter (FIL) for removing noise included in the input electric quantity of the system 2;
It comprises a multiplexer (MPX) for sampling an input electric quantity at a predetermined sampling frequency and an A / D converter (A / D) for digitally converting a signal sampled by the multiplexer.

FIG. 2 is a flow chart showing a control circuit control flow of the digital protection relay according to the first embodiment of the present invention. Next, the operation of the monitoring circuit of the analog input circuit in the digital protection relay configured as described above will be described. In the digital relay 1, when the amount of electric current and voltage of the system 2 is input to the superposition circuit 6, the superposition circuit 6 converts the amount of input electric power from the system into a predetermined amount generated from the monitoring signal generator 5. A DC voltage monitoring signal is superimposed and input to an analog input circuit 7 including an analog filter, a multiplexer, and an A / D converter. The analog input circuit 7 converts the quantity of electricity on which the monitoring signal is superimposed into a digital signal 8 at a predetermined sampling frequency and supplies the digital signal 8 to the waveform discriminating circuit 9. The waveform discriminating circuit 9 converts the digital signal 8 input from the analog input circuit 7 into the digital signal 1 of the monitoring signal.
0 and a digital signal 11 of the input electric quantity from the system 2. The digital signal 10 of the monitoring signal discriminated by the waveform discriminating circuit 9 is supplied to a monitoring circuit 12.

Conventionally, as shown in FIG. 5, the monitoring circuit 12 determines the effective value of the digital signal 10 of the monitoring signal (step S1), and determines whether the effective value is within a predetermined monitoring level range (step S1). Step S2) The presence or absence of a defect in the analog input circuit 7 is determined. If it is determined that there is no defect, the monitoring failure signal 13 is not output. If it is determined that there is a failure, the monitoring failure signal 13 is output ( Step S6).
In this case, even if there is no failure in the analog input circuit 7 of FIG. 5, if the frequency of the system 2 fluctuates, the effective value obtained above fluctuates and falls outside the monitoring level range for a predetermined time. May output the monitoring failure signal 13.

In the first embodiment, as shown in FIG. 2, the effective value of the digital signal 10 of the monitoring signal is determined by using the fact that the polarity of the effective value changes as the frequency changes. Is not within the predetermined range, at step S11, the polarity of the effective value of the monitor control circuit 13 is checked at certain time intervals.
Now, the monitoring timer is reset. Therefore, even if the effective value of the digital signal of the monitoring signal fluctuates due to the fluctuation of the system frequency, the monitoring failure signal is not output from the monitoring circuit 12.

As described above, according to the first embodiment, the monitoring control circuit 14 is added to reset the monitoring circuit 12 so as not to exceed a predetermined time. Of the monitoring circuit 12 due to unnecessary frequency detection due to the frequency fluctuation of the above can be prevented.

Second Embodiment Hereinafter, a second embodiment of the present invention will be described. The block diagram of Embodiment 2 is as follows.
The description is omitted because it is the same as FIG. 1 of the first embodiment. FIG. 3 is a flowchart showing a control circuit control flow of the digital protection relay according to Embodiment 2 of the present invention. FIG. 4 is a diagram showing an execution cycle of the digital protection relay according to the second embodiment of the present invention.

In the second embodiment, step S11 in FIG. 2 of the first embodiment is changed to step S12 in FIG. 3, and the polarity of the effective value of the digital signal 10 of the monitoring signal in the monitoring circuit control flow is changed. In the check, by synchronizing the execution cycle with the sampling frequency and making it shorter than the rated frequency, it is possible to further increase the reliability. That is, as shown in FIG. 4, the calculation is performed every shorter than the rated frequency, for example, every 210 °, the polarity of the effective value of the digital signal 10 of the monitoring signal is checked, and when the polarity changes, the monitoring timer is reset.

As described above, according to the second embodiment, an output due to unnecessary defect detection can be further prevented as compared with the first embodiment.

[0017]

Since the present invention is configured as described above, it has the following effects. In a digital protection relay for performing A / D conversion of an electric quantity having a fundamental frequency input from a power system and performing protection operation processing of the power system, a monitoring signal generator for generating a monitoring signal of a predetermined DC voltage; A superimposing circuit for superimposing the monitoring signal generated by the monitoring signal generator on the electric quantity input from the power system, and performing A / D conversion of the composite signal superimposed by the superimposing circuit at a predetermined sampling frequency. An analog input circuit; a discrimination circuit for discriminating a monitoring signal component and an electric quantity component from a digital signal formed by A / D conversion by the analog input circuit; and a monitoring signal component discriminated by the discrimination circuit. Monitors the analog input circuit for abnormalities depending on whether it is within the level range, and outputs a monitoring failure signal when abnormalities are detected. A monitoring circuit that monitors the polarity of the monitoring signal component, and prevents a monitoring failure signal from being output by the monitoring circuit when the monitoring control circuit detects the inversion of the polarity of the monitoring signal component. Therefore, it is possible to prevent unnecessary output of a monitoring failure signal of the monitoring circuit due to frequency fluctuation of the power system.

Since the monitoring control circuit monitors the polarity of the monitoring signal component in synchronization with the sampling frequency, it is possible to more reliably prevent the monitoring circuit from outputting an unnecessary monitoring failure signal. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a digital protection relay according to Embodiment 1 of the present invention.

FIG. 2 is a flowchart showing a control circuit control flow of the digital protection relay according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing a control circuit control flow of a digital protection relay according to Embodiment 2 of the present invention.

FIG. 4 is a diagram showing an execution cycle of a digital protection relay according to a second embodiment of the present invention.

FIG. 5 is a flowchart showing a monitoring control flow of a conventional digital protection relay.

[Explanation of symbols]

1 digital relay, 2 systems, 3 current transformer for instrument, 4 transformer for instrument, 5 signal generator for monitoring, 6
Superimposition circuit, 7 analog input circuit, 8 digital signal, 9 waveform discrimination circuit, 10 monitoring signal digital signal, 11 input electric quantity digital signal, 12 monitoring circuit, 13 monitoring failure signal, 14 monitoring control circuit, 15
Relay operation circuit, 16 logic circuits.

Claims (2)

[Claims] A digital protection relay for performing A / D conversion of an electric quantity having a fundamental frequency inputted from an electric power system and performing protection operation processing of the electric power system generates a signal for monitoring a predetermined DC voltage. A monitoring signal generator, a superimposing circuit for superimposing a monitoring signal generated by the monitoring signal generator on an electric quantity input from the power system, and a composite signal superimposed by the superimposing circuit at a predetermined sampling frequency. An analog input circuit for A / D conversion, a discrimination circuit for discriminating the monitoring signal component and the electric quantity component from a digital signal formed by A / D conversion by the analog input circuit, and a monitoring device discriminated by the discrimination circuit. When the abnormality of the analog input circuit is monitored based on whether the signal component is within the monitoring level range and the abnormality is detected. A monitoring circuit that outputs a monitoring failure signal, and a monitoring control circuit that monitors the polarity of the monitoring signal component. When the monitoring control circuit detects an inversion of the polarity of the monitoring signal component, the monitoring circuit detects the polarity of the monitoring signal component. A digital protection relay characterized in that a monitoring failure signal is not output. 2. The digital protection relay according to claim 1, wherein the monitoring of the polarity of the monitoring signal component by the monitoring control circuit is performed in synchronization with the sampling frequency.