JPS5917602B2 - Automatic detection method for electric current protection detector - Google Patents

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to an automatic checking method for differential current carrying protective relays.

A frequency modulated differential current carrier protective relay method is available for multi-terminal protection of ultra-high voltage systems.

This system converts the current value at each terminal within the protection section into a frequency modulated signal, which is then transmitted and received using a microwave link to reproduce the current at each end. Based on Kirchhoff's first law, it determines that there is no internal accident if the sum of the current vectors Σi=o, and that there is an internal accident if it is Σi\0. A major feature of this system is its excellent ability to select between internal and external accidents, even in the event of an internal accident accompanied by leakage.

Since this method is for ultra-high voltage applications, high speed operation is of course required, but since most of it is made up of semiconductors, which require high precision in modulation, demodulation, waveform conversion, signal delay, etc., automatic inspection is essential to ensure high reliability.

The points to note when carrying out automatic inspection with this relay system are:
Since the modulation and demodulation characteristics play such an important role in determining the relay characteristics, consideration must be given to being able to carry out comprehensive inspections that include this part.

Generally, in automatic inspection of a differential force type, it is sufficient to reverse or set the current vector of either the own end or the opposite end to zero.

However, even if the signal at the other end is inverted, since the signal at the other end is a frequency modulated signal, in order to inspect the demodulator as well, it is necessary to prepare a modulator dedicated to inspection for vector inversion, perform frequency modulation with a specified inspection current that is 180° out of phase with the current at the own end, and switch this modulator output with the signal at the other end during inspection and apply it to the demodulator.

When inverting the local signal, it is best to invert the local CT secondary current in order to perform a wide-area inspection.

On the other hand, the former requires the addition of a switching circuit and a modulator for inspection purposes, which poses problems in terms of reliability and economy.

In the latter case, the inverted signal is also sent to the other end as a frequency modulated signal, which is equivalent to an internal fault at the other end, causing a trip command to be issued.

This method has the disadvantage that a lock signal must be sent to the other end in advance using a dedicated information transmission route, and that the lock must be released after the inspection to proceed with the inspection.

It may be possible to perform the self-terminal current reversal immediately before the differential judgment section, but this cannot be adopted because it would not be a wide-area inspection.

An object of the present invention is to provide a method for easily and reliably performing automatic checking of a differential current carrying protective relay including a demodulator, without the drawbacks of the prior art described above, and capable of performing the same independently at each end.

In the present invention, if the area conversion pulse train generated during the demodulation process of the frequency modulated signal is inverted, the phase of the demodulated waveform will also be 18.
By adding a simple inversion command section to the demodulation circuit section of the self-end or the other end, the external command for automatic inspection can be used.
A major feature of this system is that it allows internal accident simulation without causing any inconvenience to the other end by reversing the signal.

The present invention will be specifically described below based on one embodiment.

FIG. 1 is a block diagram of one end of a frequency modulated relay embodying the automatic checking method of the present invention, and for simplicity of explanation only one phase of the relay is shown.

The instantaneous value of the system current from the current transformer CT is input to a known current-voltage converter 1, a known voltage-frequency converter 2 for converting the voltage into a frequency, and a known buffer amplifier 3 for making the output of the current-voltage converter 1 a predetermined magnitude and preventing load fluctuations from affecting other parts.
, a known resistance attenuator group 4 for adjusting the transmission and reception levels
It is connected to a microwave carrier terminal device (abbreviated as carrier terminal in Figure 1) 6 via a group of communication transformers 5 for impedance matching with the communication device and for insulation, and a frequency modulated signal proportional to the amplitude of the input current is transmitted to the other two terminals of the three-terminal system via output cables 7 and 8.

The frequency modulated signal from the other end is sent through cables 9 and 1.
0 through the corresponding isolation transformer 5 and resistance attenuator 4,
The signal is input to a relay determination unit 14 via a known delay circuit 11 and frequency-voltage converters 12 and 13 which demodulate the frequency-modulated signal back to the original voltage signal.

The frequency modulated signal from one end enters the relay determination unit 14 via a known delay circuit 15 which compensates for the transmission delay from the other two terminals, and a frequency-to-voltage converter 16 having the same characteristics as 12 and 13 which demodulates the delayed frequency modulated signal from the own end.

In 14, a vector operation is performed based on the demodulated signal of each terminal to obtain the operating force required for relay operation, and a scalar sum operation is performed to obtain the suppressing force. If the operating force overcomes the suppressing force, it is determined that an internal accident has occurred and a trip command is issued.

The delay compensation units 11 and 15 set the compensation value in accordance with M7 at the terminal with the largest transmission delay.

Reference numeral 17 denotes a control command terminal for inverting the waveform of the local frequency-to-voltage converter 16 during automatic inspection.

The frequency-to-voltage converters 12, 13 and 16 for each terminal are shown in detail in FIG.

Reference numeral 18 denotes a known Schmitt circuit, 19 denotes a known monostable multivibration break, and 20 denotes a known low-pass filter.

The frequency modulated signal shown in FIG. 2-1 is fed to the Schmitt circuit 18.
As a result, the signal is ON when the signal is at or above the L level and OFF when the signal is below the LLL level, resulting in a rectangular wave as shown in 11.

In the monostable multivibrator 19, the rising and falling edges of this rectangular wave are triggered, and a pulse train of a constant width is generated as shown in FIG.

Reference numeral 20 denotes a gate circuit which is adapted to input either an inverted or non-inverted output to a low-pass filter 21 in response to an external command 17 .

To briefly explain this filter, it can be thought of as a kind of integrator circuit that discharges at the mark portion of a pulse input and charges at the space portion.

Therefore, when a time-series pulse signal in which the ratio of mark portions to space portions changes as shown in FIG. 2 111 is applied, the output repeats charging and discharging in the short term and increases or decreases in the long term.

Figure 2, part 1 shows only this long-term component.
By using a filter that also removes short-term components,
It is clear that the original current signal can be reproduced.

It is already known that voltage to frequency converters work in this manner.

Here, assuming that the charging time constant and discharging time constant of low-pass filter 21 are equal, if the proportion of the time occupied by spaces is greater, the output of filter 21 increases, and if the proportion of the time occupied by marks is greater, the output of filter 21 decreases.

Therefore, when an external command 17 for inspection is given and the output of the monostable multivibrator 19 is inverted, the ratio of the mark portion to the space portion is inverted, and the filter output obtained at this time is the inversion of the original filter output.

This can also be understood from the fact that while the filter output for a non-inverted pulse train tends to increase, the filter output for an inverted pulse train tends to decrease.

In this way, a simulated internal fault signal is obtained.

FIG. 3 shows the gate control unit 20 in detail.

In the figure, 46 and 47 are AND gates, 48 and 52 are impulses, and 49 is an OR gate. A terminal 50 is connected to the output of the monostable multivibrator 19 (hereinafter referred to as A).

), and a check command signal to terminal 17 (hereinafter referred to as B).

If the output of each part is logically expressed in Boolean algebra using input signals A and B, the output of 48 is 100, the output of 52 is X, the output of 41 is A-B, the output of 46 is A·B1, and the output of 51 is A-B+A-B.

The normal inspection command signal B is set to 0'', so that the final output is A, and the input to terminal 50 becomes the output of terminal 51 as it is.

At the time of inspection, the signal B becomes "1", and an inverted output A of the input A is obtained at the terminal 51.

Since this embodiment is as described above, no special additional circuit such as an inspection power supply is required.

By simply adding a simple gate circuit to the local frequency voltage converter, it is possible to perform automatic inspection of a wide range, including the modulation/demodulation section, without affecting the remote terminal.

In this embodiment, the case where inversion is performed by the frequency-voltage converter at the own end has been described, but it goes without saying that the same results can be obtained by inverting the frequency-voltage converters 12 and 13 at the other end.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the concept of an embodiment of the present invention.
The figure shows an example of a frequency-to-voltage converter of the present invention and a block diagram and waveform diagram showing its operation, and FIG. 3 shows an example of a gate circuit that can be used in the present invention. 18... Schmitt circuit, 19... Monostable multi-vibration break, 20... Gate circuit, 21... Low-pass filter, 10...
Monostable multi output terminal, 11...Low-pass filter input terminal.

Claims (1)

[Claims] 1. A differential current carrier protective relay that frequency-modulates the current signals at each end and transmits them mutually via a transmission line to determine whether protection is required, and in order to demodulate the frequency-modulated signal from each end, the system comprises a first means for converting the frequency-modulated signal into a rectangular wave, a second means for giving a pulse of a constant width at the rising or falling point of the rectangular wave of said means, and a low-pass filter for extracting a signal corresponding to the ratio of the mark portion and the space portion of the pulse train of said means, and during automatic inspection of the differential current carrier protective relay, the phase of the pulse train of the output of the second means is inverted to invert the phase of the demodulated waveform of the low-pass filter output, thereby simulating an internal accident.