JP2001327064A - Monitoring device for protective relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective-relay monitoring device for surely detecting failures, even in a filter circuit. SOLUTION: A first monitoring signal at a cut-off frequency fa or a nearby frequency f1≈fa related to the characteristics of a low-cut high-pass filter included in an integrator 19, and a second monitoring signal at a cut-off frequency fb or nearby frequency f2≈fb related to the high-cut low-pass characteristics of an analog filter 5, are entered into a monitoring winding 18 of an input transformer 15. The factors for the frequencies f1 and f2 are extracted by a digital processing unit 12, and the digital processing unit 12 generates an apparatus abnormality signal, when a change of amplitude is exceeds a prescribed range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection relay monitoring device for monitoring abnormalities of a digital protection relay device itself, and more particularly to a digital protection relay monitoring device using an air-core type input transformer.

[0002]

2. Description of the Related Art FIG. 5 shows a digital protection relay monitoring apparatus described in, for example, Japanese Patent Publication No. 3-79931. In the figure, 1 is a transmission line, 2 is a primary current transformer provided in the transmission line 1, 3 is an input transformer with a core that further converts the output current of the primary current transformer 2, 4 is an input transformer 3
Of the input transformer 3 to convert the output of the
A load resistor connected between the next winding terminals, 5 is an analog filter for removing low frequency or high frequency components of the output signal of the input transformer 3, 6 is an output from the analog filter 5 at an arbitrary fixed period, A sample-and-hold for holding for a predetermined time, 7 a monitor signal generator for generating a monitor signal, 8 an amplifier for amplifying the output of the monitor signal generator 7,
9 is a monitoring winding for inputting a monitoring signal from the amplifier 8, 10 is a multiplexer for switching the signal held by the sample hold 6, and 11 is a multiplexer 10
An A / D converter for quantizing a signal from the A / D converter 12 is a digital processing unit for digitally processing an output signal of the A / D converter 11.

FIG. 5 shows three-phase components (a, b,
c) and a zero-phase component (o), and shows the current measurement system corresponding to the zero-phase component (o). Since each phase has the same configuration, the illustration of the b and c phases is omitted here, and only the a phase and the zero phase o It is shown and indicated by the suffix of the code. The voltage measurement system is omitted.

[0004] The digital processing unit 12 creates a protection relay signal that is output in response to a change in the current and voltage signals to be detected and a device abnormality signal that is output in response to a change in the monitoring signal. The operation as a protection relay will be described. The current signal of the transmission line 1 detected by the primary current transformer 2 is input to the analog filter 5 via the input transformer 3. In digital protection relays, comprehensive filter characteristics required from various relay characteristics are realized by a combination of digital processing and analog processing. The main purpose of the analog filter 5 is to remove a harmonic component having a frequency equal to or higher than a return frequency for preventing generation of a return signal, which is a problem during A / D conversion. The output signal of the analog filter 5 is sampled simultaneously for all input channels by the sample and hold 6 and is converted to a digital value by the A / D converter 11. In this way, the input signal of the power system to be detected is processed, a relay operation is performed, and a necessary protection relay signal is output.

Next, the operation of the digital protection relay monitoring apparatus for performing the above signal processing will be described. A secondary output of the primary current transformer 2 based on the system current I flowing through the transmission line 1 and a monitoring signal flowing through the monitoring winding 9 are input to the input transformer 3 having a core. Thus, the monitoring signal is constantly superimposed on the system current signal. The current supplied to the monitoring winding 9 is obtained by amplifying the output signal of the monitoring signal generator 7 by the amplifier 8, and the monitoring winding 9 maintains a constant frequency and current value. As described above, the monitoring signal is converted into a digital value via the input transformer 3, the analog filter 5, the sample and hold 6, the multiplexer 10, and the A / D converter 11. The digital data from the A / D converter 11 is sampled and A / D-converted at a convenient cycle, generally at intervals of 30 electrical degrees of the system frequency in the above-described relay algorithm.
These digital data are subjected to an extraction process of a monitoring signal component by a digital processing unit 12, and the magnitude of the extracted monitoring signal is checked, so that the A / D converter 1 is input from the input transformer 3.
1 is detected, and an "alarm signal" is output from the digital processing unit 12 as shown in FIG.

Next, the frequency of the monitor signal is changed to the system frequency of 4
A method of extracting a monitoring signal component will be described by taking, as an example, a case where the setting is doubled. That is, the frequency characteristic of the digital filter for extracting the monitoring signal is expressed by equation (1). G = 2 | cos (nπ / 2) | (1) G: output multiple with respect to input n: multiple of filter input frequency with respect to system frequency In equation (1), system frequency (n = 1), monitor signal frequency (n)
= 4) is obtained as follows: System frequency... (N = 1) G = 2 | cos (π / 2) | = 0 (2) Monitoring signal frequency... (N = 4) G = 2 | cos (4π) / 2) | = 2 (3) As shown in FIG. 6, the signal of the system frequency is removed and the signal of the monitor signal frequency is doubled and extracted. FIG.
Shows the frequency characteristic of the equation (1). Since the size of the monitoring signal is known, the digital processing unit 12
By comparing with a preset threshold value, a circuit failure from the input transformer 3 to the A / D converter 11 can be detected.

In order to perform the function as a protection relay, it is necessary to remove a monitoring signal component. As an example, as described above, the frequency of the monitoring signal is
The case where the number is doubled will be described as an example. In order to remove the frequency component of the monitor signal, digital filter processing shown by the equation (4) is performed. G = 2 | cos (nπ / 4) | (4) G: output multiple for input n: multiple of filter input frequency for system frequency In equation (4), system frequency (n = 1), monitor signal frequency (n)
= 4) is obtained as follows: System frequency... (N = 1) G = 2 | cos (π / 4) | = √2 (5) Monitoring signal frequency... (N = 4) G = 2 | cos ( 4π / 2) | = 0 (6), and the signal component of the system frequency is extracted as shown in FIG. FIG. 7 shows the frequency characteristic of equation (4).

[0008]

The conventional protection relay monitoring device is configured as described above, and is effective when applied to a device using an iron core type input transformer. It is not effective when applied to a device using a type in which an air-core type is combined with an integrator for integrating the output of its secondary winding. That is,
In the case of the above combination, a low (low frequency) cut circuit is usually added to the integrator so that the integrator does not integrate the low frequency signal and saturate. There is a drawback that failure detection of the range cut circuit becomes impossible. Further, in the conventional monitoring method, depending on the type of the monitoring signal, a failure of the analog filter itself may not be detected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a protection relay monitoring device capable of reliably detecting a failure in a filter circuit portion.

[0010]

A protection relay monitoring device according to the present invention includes a monitoring signal generator for generating a monitoring signal, a primary winding to which a signal to be detected is input, and a monitoring winding to which the monitoring signal is input. An air-core type input transformer having a wire and a secondary winding magnetically coupled to both windings, an integrator having low-cut filter characteristics and integrating a signal from the secondary winding, a high-cut filter An analog filter having characteristics and adjusting a frequency characteristic of a signal from the integrator, an A / D converter for converting a signal from the analog filter into a digital signal, and processing a signal from the A / D converter Thus, a protection relay monitor having a digital processing unit for creating a protection relay signal output in response to a change in the detection target signal and an equipment abnormality signal output in response to a change in the monitoring signal. An apparatus, in which the frequency of the monitoring signal generated by the monitor signal generator is set to the frequency of the cutoff frequency or near the filter characteristics.

A monitoring signal generator of the protection relay monitoring device according to the present invention generates first and second monitoring signals, and the frequency of the first monitoring signal is a cutoff of a filter characteristic of the integrator. The frequency is set to a frequency or a frequency near the frequency, and the frequency of the second monitoring signal is set to a cutoff frequency of a filter characteristic of the analog filter or a frequency near the cutoff frequency.

Further, in the protection relay monitoring device according to the present invention, both the first and second monitoring signals are input to the monitoring winding of the input transformer.

In the protection relay monitoring apparatus according to the present invention, the first monitoring signal is input to a monitoring winding of an input transformer, and the second monitoring signal is directly input to an analog filter. .

Further, in the protection relay monitoring apparatus according to the present invention, the filter characteristic of the analog filter is a band-pass characteristic having a cutoff frequency on a high frequency side and a low frequency side, and Is higher than the cutoff frequency of the filter characteristic of the integrator, the monitor signal generator performs the third monitor of the lower cutoff frequency of the analog filter or a frequency near the lower cutoff frequency in addition to the first and second monitor signals. Signal and the first
The monitoring of the monitoring signal is performed based on the signal derived from the integrator and A / D converted without passing through the analog filter.

The digital processing section of the protection relay monitoring device according to the present invention outputs a device abnormality signal when a change in the amplitude of the detected monitoring signal exceeds a predetermined set range.

Further, the digital processing section of the protection relay monitoring device according to the present invention outputs a device abnormality signal when a change in the phase of the detected monitoring signal exceeds a predetermined set range.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a configuration diagram showing a protection relay monitoring device according to Embodiment 1 of the present invention. FIG. 1 shows only the current detection system, and the three-phase components (a, b, c) and the zero-phase component (o) have the same configuration. Only the a phase shown is shown. In FIG. 1, reference numeral 1 denotes a transmission line in which a system current I to be detected flows, 2 denotes a primary current transformer provided in the transmission line 1, and 15 denotes an air-core type input transformer, and a secondary output of the primary current transformer 2. Primary winding 1 to which is input
6, a secondary winding 17 for taking out an output to an integrator 19 described later, and a monitoring winding 18 to which a monitoring signal also described later is input.

Reference numeral 19 denotes a secondary winding 17 of the input transformer 15.
This is an integrator that integrates and outputs the signal from the inverter, and has a low-cut filter characteristic by setting constants of each resistor and capacitor to predetermined values, as described later.
Reference numeral 5 denotes an analog filter having a high-cut filter characteristic for removing harmonic components equal to or higher than the return frequency, as in the prior art, and reference numeral 6 denotes a sample hold for holding the output from the analog filter 5 at a constant period for a fixed time.

Reference numeral 20 denotes a monitor signal generator, which includes a reference signal generator 21 for generating a monitor signal, and an amplifier 22 for amplifying the monitor signal from the reference signal generator 21. Here, the monitoring signal generator 20 outputs two monitoring signals of frequencies f1 and f2, as described later. 10 is a multiplexer for switching the signal held by the sample hold 6, 11 is an A / D converter for quantizing the signal from the multiplexer 10, and 12 is a digital signal processing of the output signal of the A / D converter 11. A digital processing unit that creates a protection relay signal that is output in response to a change in the current detection signal and a device abnormality (alarm) signal that is output in response to a change in the monitoring signal.

FIG. 2 shows the frequency characteristics of the components shown in FIG. 1. FIG. 2A shows the frequency characteristics of the input transformer 15, and the frequency and the gain are proportional to each other. FIG.
(B) is a frequency characteristic of the integrator 19, wherein the frequency and the gain are in an inversely proportional relationship, and further, the gain in the low frequency range below the frequency fa is suppressed so as not to integrate the low frequency input. That is, in the integrator 19 of FIG. 1, the gain Gh of the high band is obtained by the equation (7). Gh = ωC1 / R1 (7) Further, the low-band gain Gl is obtained by Expression (8). Gl = Zr / R1 (8) Here, Zr = R2 {1+ [R3 / (R4 + (1 / ωC2))]} (9) Accordingly, the total gain Gt is obtained by the equation (10). The characteristics are shown in FIG. Gt = Gh · Gl (10)

FIG. 2C shows the frequency characteristics when the input transformer 15 and the integrator 19 are combined. The frequency characteristics are low-cut and high-pass filter characteristics having a cut-off frequency fa. FIG. 2D shows the frequency characteristics of the analog filter 5, which are high-cut and low-pass filter characteristics having a cutoff frequency fb. FIG. 2E shows a total frequency characteristic when the input transformer 15, the integrator 19, and the analog filter 5 are connected in series, and has a low-frequency cutoff frequency fa and a high-frequency cutoff frequency fb. ing.

Next, the operation of the original protection relay will be described. The secondary output signal of the system current I to be detected passes through the primary current transformer 2 and is input to the primary winding 16 of the input transformer 15. A differential signal is obtained from the secondary winding 17 magnetically coupled to the primary winding 16, and this is integrated by an integrator 19 to be output as a current signal. This signal is further filtered by the analog filter 5 to remove high-frequency components higher than the return frequency.
This is sampled by the sample and hold 6, quantized by the A / D converter 11 via the multiplexer 10, and then relayed by the digital processing unit 12 to output a necessary protection relay signal.

Next, a description will be given of the operation of monitoring the failure of the device with built-in device, which is the subject of the present invention. In the protection relay monitoring device according to the first embodiment, the monitoring signal generator 20 generates a monitoring signal having two types of frequencies f1 and f2 having the following relationship. f1 ≒ fa… (11) f2 ≒ fb… (12)

Here, as described with reference to FIG. 2, fa is the cutoff frequency fa of the low cut filter characteristic of the integrator 19, and the frequency f1 of the first monitor signal is the frequency f1.
Set to a value equal to or near a. Further, fb is the cutoff frequency fb of the high cut filter characteristic of the analog filter 5, and the frequency f2 of the second monitor signal is set to a value equal to or near this frequency fb.

The monitoring signals of the frequencies f1 and f2 are input to the monitoring winding 18, and thereafter, are constantly superimposed on the current signal to be originally detected by the relay, so that the input transformer 15, the integrator 19,
The signal passes through an analog filter 5, a sample hold 6, a multiplexer 10, and an A / D converter 11 to reach a digital processing unit 12, where necessary digital processing is performed. That is, in the digital processing unit 12, the frequency f
1, the signal component of f2 is extracted, and the failure of the internal device is monitored from the change in the level.

Here, the observed waveform abnormalities when a failure occurs in a component in the analog circuit from the input transformer 15 to the analog filter 5 are listed as follows. Failure of input transformer 15 (1) Disconnection of primary winding 16: System frequency signal cannot be observed. (2) Disconnection of the monitoring winding 18: The monitoring signals f1 and f2 cannot be observed. (3) Disconnection of secondary winding 17: system frequency, monitor signal f
1, f2 cannot be observed. Failure of the integrator 19 (3) Disconnection of the resistor R1: system frequency signal, monitor signal f1,
f2 cannot be observed. (4) Disconnection of the capacitor C1: The monitoring signals f1 and f2 components rise to the power supply voltage. The system frequency signal and the monitoring signals f1 and f2 become unobservable. (5) Disconnection of resistor R2 or R3: DC component rises to power supply voltage. (6) Disconnection of capacitor C2: System frequency signal and monitoring signals f1 and f2 cannot be observed. (7) Disconnection of resistor R4: The monitor signal f1 component rises to the power supply voltage. There is no change in the monitoring signal f2 component. The failure of the analog filter 5 is determined by the digital protection relay f
Detection is possible by observing the two components.

As a specific example of setting the frequency, the frequency f1 of the monitoring signal is set to, for example, 1 Hz, and the frequency f2 is set to, for example, 480 Hz for a system frequency of 50 Hz or 60 Hz. Therefore, the digital processing unit 1
In step 2, the S / W processing in the CPU extracts a component of a system frequency of 50 Hz or 60 Hz and a sub-harmonic component and a harmonic component of a predetermined range as necessary, and operates as an original protection relay. At the same time, a frequency component of f1 = 1 Hz and f2 = 480 Hz is extracted, and when one or both of the extracted signals exceeds a predetermined set range, this is detected and a monitoring operation of outputting a device abnormality (alarm) signal is performed. Do.

As a change observation target when judging the occurrence of a failure from the extracted change in the monitoring signal, an amplitude change of the monitoring signal may be observed. Since the phase also changes, the phase of the monitoring signal may be detected, and this may be used as an observation target to determine the failure. The same applies to the following embodiments.

Embodiment 2 FIG. 3 is a configuration diagram showing a protection relay monitoring device according to Embodiment 2 of the present invention.
Hereinafter, a description will be given focusing on portions different from the first embodiment. In the second embodiment, a band-pass filter 23 is used as an analog filter instead of the high-pass filter in the first embodiment. This is adopted from the originally required specification of the protection relay operating characteristics. In this case, the bandpass filter 23 has a cutoff frequency fc on the low frequency side in addition to the cutoff frequency fb on the high frequency side. The frequency fc is, for example, about 10 Hz, and fa <fc <fb.
Is established.

As described above, in the protection relay monitoring device according to the second embodiment, the monitoring signal generator 20 generates monitoring signals having three types of frequencies f1, f2, and f3 having the following relationship. f1 ≒ fa ... (13) f2 ≒ fb ... (14) f3 ≒ fc ... (15) In this case, the monitoring signal f1
Since cannot pass through the band-pass filter 23, the f1 component is input from the integrator 19 directly to the digital processing unit 12 via the sample hold 6-1 as shown in FIG.

Accordingly, the digital processing section 12 extracts the f1, f2, and f3 components of the monitor signal by S / W processing of the CPU, and integrates the change of the monitor signal f1 with the input transformer 15 based on the change of the extracted monitor signal f1. The failure of the device 19, the failure of the component forming the high-pass characteristic of the band-pass filter 23 from the change of the monitoring signal f2, and the failure of the component forming the low-pass side of the band-pass filter 23 from the change of the monitoring signal f3. Failures of the components to be formed can be reliably detected.

Embodiment 3 FIG. FIG. 4 is a configuration diagram showing a protection relay monitoring device according to Embodiment 3 of the present invention.
Hereinafter, a description will be given focusing on portions different from the above embodiment. In the third embodiment, the monitor signal of the frequency f1 generated by the reference signal generator 21 of the monitor signal
1 is input to the monitoring winding 18 of the input transformer 15.
On the other hand, the monitoring signal of the frequency f2 is directly input to the analog filter 5 from the amplifier 22-2. Analog filter 5
Has the same low-cut and high-pass filter characteristics of the same cutoff frequency fb as in the first embodiment.

In the digital processing unit 12, the first embodiment
As in the case of (1), the components of the monitoring signals f1 and f2 are extracted, the presence or absence of a failure in the input transformer 15 and the integrator 19 is determined from the change in the extracted monitoring signal f1, and the change of the analog filter 5 is determined from the change in the monitoring signal f2. Determine whether there is a failure. In this case, in particular, since the monitoring signal f2 is directly input to the analog filter 5 to be monitored, there is an advantage that the failure occurrence site can be determined with higher accuracy.

In the above-described embodiment, the cutoff frequency of each filter characteristic or a frequency near the cutoff frequency is used.
The configuration is such that monitoring signals of various types or three types of frequencies are simultaneously generated to perform fault monitoring of each unit. However, depending on the configuration of the analog circuit, a configuration in which monitoring signals of more types of frequencies are generated and fault monitoring is performed. Needless to say, attention may be paid to the filter characteristic of one part, and one type of monitoring signal having a cutoff frequency of the filter characteristic or a frequency in the vicinity thereof is generated to perform failure monitoring of the part. You may.

[0035]

As described above, the protection relay monitoring apparatus according to the present invention comprises a monitoring signal generator for generating a monitoring signal, a primary winding to which a detection target signal is input, and a monitoring to which the monitoring signal is input. An air-core type input transformer having a winding and a secondary winding magnetically coupled to both windings; an integrator having low-cut filter characteristics for integrating a signal from the secondary winding; An analog filter having a filter characteristic for adjusting a frequency characteristic of a signal from the integrator, an A / D converter for converting a signal from the analog filter into a digital signal, and processing a signal from the A / D converter By doing so, a protection relay monitor having a digital processing unit that creates a protection relay signal that is output in response to a change in the detection target signal and an equipment abnormality signal that is output in response to a change in the monitoring signal is provided. An apparatus, since the frequency of the monitoring signal generated by the monitor signal generator is set to the frequency of the cutoff frequency or near the filter characteristics,
It is possible to reliably determine whether a failure has occurred in a portion forming the filter characteristic.

The monitoring signal generator of the protection relay monitoring device according to the present invention generates first and second monitoring signals, and the frequency of the first monitoring signal is a cutoff of a filter characteristic of the integrator. Since the frequency of the second monitoring signal is set to a frequency close to the cutoff frequency of the filter characteristic of the analog filter or a frequency close to the cutoff frequency,
It is possible to reliably determine whether or not a failure has occurred in the integrator and the analog filter.

In the protection relay monitoring device according to the present invention, both the first and second monitoring signals are input to the monitoring winding of the input transformer, so that the circuit configuration of the monitoring device is simplified. Becomes

In the protection relay monitoring device according to the present invention, the first monitoring signal is input to the monitoring winding of the input transformer, and the second monitoring signal is directly input to the analog filter. The failure site can be determined with higher accuracy by the monitoring signal.

Further, in the protection relay monitoring apparatus according to the present invention, the filter characteristic of the analog filter is a band-pass characteristic having a cutoff frequency on the high frequency side and a low frequency side, and the cutoff frequency on the low frequency side is reduced. Is higher than the cutoff frequency of the filter characteristic of the integrator, the monitor signal generator performs the third monitor of the lower cutoff frequency of the analog filter or a frequency near the lower cutoff frequency in addition to the first and second monitor signals. Signal and the first
Is monitored based on the signal derived from the integrator and A / D-converted without passing through the analog filter, so that the input transformer and the integrator are not only failed, but also the high-frequency range of the analog filter is monitored. It is possible to reliably detect all failures of components forming the side characteristic and the low-frequency side characteristic.

Further, the digital processing section of the protection relay monitoring device according to the present invention outputs a device abnormality signal when the detected change in the amplitude of the monitoring signal exceeds a predetermined set range. Is surely done.

Also, the digital processing section of the protection relay monitoring apparatus according to the present invention outputs a device abnormality signal when the detected change in the phase of the monitoring signal exceeds a predetermined set range. Is surely done.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a protection relay monitoring device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating frequency characteristics of the analog circuit portion of FIG.

FIG. 3 is a configuration diagram illustrating a protection relay monitoring device according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram illustrating a protection relay monitoring device according to a third embodiment of the present invention.

FIG. 5 is a configuration diagram showing a conventional protection relay monitoring device.

FIG. 6 is a diagram illustrating frequency characteristics of the digital filter of FIG.

FIG. 7 is a diagram illustrating frequency characteristics of the digital filter of FIG. 5;

[Explanation of symbols]

5 analog filter, 11 A / D converter, 12 digital processing unit, 15 input transformer, 16 primary winding, 17 secondary winding, 18 monitoring winding, 19 integrator,
20, 24 monitoring signal generator, 23 bandpass filter.

Continuing from the front page (72) Nozomi Suzuki, 2-3-2 Marunouchi, Chiyoda-ku, Tokyo, Japan Mitsubishi Electric Corporation (72) Inventor Tokumasa Kusan 2-3-2, Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Co., Ltd. F term in the company (reference) 2G036 AA27 BA07 BB09 BB12 CA06 CA08 5G042 BB03 BB06 BB07 BB12 GG02 GG08

Claims (7)

[Claims] A monitoring signal generator for generating a monitoring signal; a primary winding to which a detection target signal is input; a monitoring winding to which the monitoring signal is input; An air-core type input transformer having a secondary winding; an integrator having a low-cut filter characteristic for integrating a signal from the secondary winding; and a frequency characteristic of a signal from the integrator having a high-cut filter characteristic. An analog filter to be adjusted, an A / D converter for converting a signal from the analog filter into a digital signal, and a signal from the A / D converter is processed to output the signal in accordance with a change in the detection target signal. What is claimed is: 1. A protection relay monitoring device, comprising: a digital signal processing unit for generating a protection relay signal and a device abnormality signal to be output in response to a change in the monitoring signal, wherein the monitoring signal generated by the monitoring signal generator is provided. Protection relay monitor the frequency of the is characterized in that setting the frequency of the cutoff frequency or near the filter characteristics. 2. A monitor signal generator generates first and second monitor signals. The frequency of the first monitor signal is set to a cutoff frequency of a filter characteristic of the integrator or a frequency near the cutoff frequency. 2. The protection relay monitoring device according to claim 1, wherein the frequency of the second monitoring signal is set to a cutoff frequency of a filter characteristic of the analog filter or a frequency near the cutoff frequency. 3. The protection relay monitoring device according to claim 2, wherein both the first and second monitoring signals are input to a monitoring winding of an input transformer. 4. The protection relay monitoring device according to claim 2, wherein the first monitoring signal is input to a monitoring winding of an input transformer, and the second monitoring signal is directly input to an analog filter. . 5. The filter characteristic of an analog filter is a band-pass characteristic having a cutoff frequency on a high frequency side and a low frequency side, wherein the low cutoff frequency is lower than a cutoff frequency of a filter characteristic of an integrator. If it is high, the monitor signal generator generates a third monitor signal having a frequency at or near the lower cutoff frequency of the analog filter in addition to the first and second monitor signals, and the first monitor signal. 3. The protection relay monitoring device according to claim 2, wherein the signal is monitored based on a signal derived from the integrator and A / D converted without passing through the analog filter. 6. The protection according to claim 1, wherein the digital processing unit outputs an equipment abnormality signal when a change in the amplitude of the detected monitoring signal exceeds a predetermined setting range. Relay monitoring device. 7. The protection according to claim 1, wherein the digital processing unit outputs a device abnormality signal when a change in the phase of the detected monitoring signal exceeds a predetermined setting range. Relay monitoring device.