JPS5835015B2 - Malfunction prevention method for frequency modulation protection relay device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing malfunction of a frequency modulation protective relay device, and particularly relates to frequency modulation noise that has been discovered by the present inventors to harm the protective operation of the protective relay device. related to taking measures against

A frequency modulation protective relay (hereinafter simply referred to as FM'J relay) is already well known and is generally constructed as shown in FIG.

In the figure, La, Lb, and Lc are power transmission lines for each phase, and each phase current IAa, IAb, IAc, IB
a, IBb, and IBc are current transformers CTAatCTAbtCTA ct CTB installed at each electric station A and H.
The signals are taken into the protective relay devices RYA and RYB of each electric station A and B via a t CTB b t CTB c, respectively.

RYA and RYB are respectively a first modulator MA1°MBI and a second demodulator DA2. It consists of DB2, relay determination sections EA and EB.

First, in MA 1 and MA 2, each phase current of 50 or 60 (Elz) as shown in Figure 2 a is
For example, if the center frequency is 1.8Kt (z and its ±IKH)
z-range frequency domain signal (FIG. 2b).

This is so-called frequency modulation, and a 1.8 KHz signal is given when the phase current is at zero value.

18 +1 (KHz) for the maximum positive value and the maximum negative value that can be predicted.

A frequency signal of 1,8-1 (KHz) is given.

The signal after modulation is shown in Figure 2, and as is clear by comparing it with the phase current in Figure 2A, it is clear that the more positive input values required, the denser the period, and the thicker the negative input values. It is considered to be a frequency signal with a sparse period.

MAl. Three outputs of MHI, MAl 1 , MA
I 2゜MAI 3. MBI 1, MBI 2. M.B.
All l3 are frequency modulated signals in the range of 18±1 (KHz).

The outputs of these MAI and MBI are sent to the other end electrical station via the signal transmission device SF.

This SF is the second modulation unit MA2. It consists of MB2, first demodulator DAI, and DB1.

Signal transmission in this SF may be carried out by either a so-called frequency division multiplexing method or a time division multiplexing method, and the second modulation unit MA2. MB2 uses multiple human inputs including frequency modulation signals for phase currents (other inputs include voice signals from telephones, etc., signals for monitoring and controlling electrical stations, etc.).

) are collectively transmitted as one carrier wave to the other end, and the first demodulator DAI.

DBI reproduces the original frequency modulated signal from the carrier wave.

The transmission system of this signal transmission device SF is already well known, but if we describe an example of the frequency division multiplexing system, its general operation can be expressed as shown in FIG. 2C.

First, with the frequency modulation signal MA11 in the range of 18±1(K)-h) corresponding to the a-phase current, 1.4 (KHz
) modulates the modulated wave with the center frequency.

Similarly, with MAl2 of 18±1 (KHz), 18
The modulated wave whose center frequency is (KHz) is modulated.

Furthermore, with MAl3 of 1.8 ± 1 (KHz) 22 (
The modulated wave whose center frequency is kHz) is modulated.

Then, the modulated wave having a center frequency of 66(Kl(z)) is further modulated with a signal in the range of 12 to 24(fG(z)) to obtain a signal MD.

This MDl is composed of three frequency modulated signals MAI 1 , MA
I 2 and MAl 3 are combined into one signal, and this process is generally called grouping.

In addition, using the same method, other than phase current 1.8±
1 (K, Hz) frequency modulated signal MA21
, MA22, and MA23 are also grooved and made into one signal of MD2.

These MD12MD2 modulate higher-order modulated waves,
Finally, it is transmitted as one carrier wave.

Second demodulator DA2. The DB2 reproduces the current waveform of each phase at the other end by frequency demodulation (an operation opposite to frequency modulation).

As a result, the relay determination unit EA compares the currents of the mutually corresponding phases of each electric station, and detects an internal fault in the power transmission line based on the concept of the well-known current differential protection method.

In other words, in the case of this FMIJ relay, the polarity of the current transformer etc. is taken into consideration so that the difference current between both ends becomes zero with respect to an external fault current or normal load current, and a difference current appears only in the case of an internal fault.

When an internal accident is detected, a breaker (not shown) of each electric station is opened.

This FMIJ relay has already been put into practical use, and as described above, in principle it should not generate a differential current with respect to the passing current in the event of an external fault.

However, in actual operation, we experienced that a difference current was generated despite the passing current.

And this is the first modulation section MA1. M) Comparing the frequency modulated signal of 31 and the frequency modulated signal input to the second demodulators DBI and DA1 at each instant, there is a discrepancy. The inventors' investigation revealed that there is a cause.

This phenomenon is equivalent to noise being superimposed on the first modulation reduction force, and affects the magnitude and frequency of the frequency modulation signal.
This is why it is called frequency modulation noise (hereinafter simply referred to as FM noise).

It is known from experience that this FM noise tends to occur when the frequency is close to the center frequency, that is, when the current input is near zero, and the frequency deviation can reach as much as 50 (Hz).

When converting this frequency deviation into a current value, it is ±5%
This means that if we consider something like a protective relay, which operates when the difference in current between both ends is ±5% or more, it will malfunction.

Of course, even in the case of a differential type protective relay, a suppressing force is applied to prevent unnecessary malfunctions, but when the current is small, the suppressing force is also small, so this is a perfect way to prevent malfunctions. I can't hope for that.

Of course, the cause of this FM noise has been investigated, but ultimately the root cause remains unknown, and only two or three factors that have been found to have a causal relationship with FM noise have been addressed.

An example of a countermeasure is to stabilize the oscillator power supply that provides the reference frequency of the modulated wave when frequency division multiplexing transmission is used, and to prevent sudden changes in the number of poles when starting and stopping float charging in the battery power supply. By doing so, it was possible to suppress the generation of FM noise.

As described above, from the perspective of removing the cause, the cause is unknown, and even when the cause is identified, it is not necessarily easy to take complete measures.

Therefore, in the end, the generated FM noise is detected and the FM,
Although there is no choice but to take measures to prevent IJ tray malfunction, there is a problem that FM noise cannot be detected.

For example, it has been known to detect noise by capturing frequencies outside the used frequency band, but in most cases, the FM noise that is the subject of the present invention is within the used frequency band (as mentioned above, near the center frequency). Easy to occur, 50 (Hz)
It is of a certain degree.

), it cannot be distinguished by monitoring the received frequency modulated signal itself.

As described in detail above, since the cause of FM noise cannot be removed, the present invention aims to detect FM noise and take measures to prevent malfunction of the FMIJ relay.

In the present invention, a pilot signal of a constant frequency (for example, the center frequency of modulation in the first modulation section) is used together with the frequency modulation signal of each phase current.

) are also given to the signal transmission device and sent and received as a carrier wave all at once.

Therefore, both signals should be placed under the same environment, and FM
It is also affected by noise, and FM noise can be detected by monitoring the received pilot signal of a certain frequency or its frequency demodulation signal.

FIG. 3 shows an embodiment of the present invention.

In this figure, the same reference numerals as in FIG. 1 indicate the same thing or the same animal, and the differences from FIG. 1 will be mainly explained.

First, regarding the signal sending side, the protective relay device RY receives the pilot signal MA14. Also outputs MB14.

This signal is obtained by frequency modulating a constant value given by the power source E, and is modulated together with other frequency modulated signals as shown in FIG. 2 and sent out as a carrier wave all at once.

F is the pilot signal MA obtained via the signal transmission device SF
14° MBl4 monitoring circuit, which determines whether the frequency of its receiving input is a predetermined frequency corresponding to a constant value determined by the power source E, or whether the frequency demodulated signal is the above-mentioned constant value. Monitor whether or not.

When it is determined that FM noise has occurred, relay determination units EA and EB prevent the application of a breaker disconnection signal.

Incidentally, in the present invention, the pilot signals MAI 4 , M
It is preferable that the BI 4 frequency-modulates an input close to zero (therefore, its output is 18 (KHz)), and in this case, experience shows that FM noise is most likely to be mixed in.

To explain a specific example of this monitoring/trip prevention,
In FIG. 4, each input signal MBI 1 , MBl 2 , MBl 3 is first input to the second demodulator DA2.

Demodulate MBl4, then MBI 1, MBI 2
.

MBl3 demodulated signals I B a', I B b' t
I B c' is guided to relay determination section EA.

In the relay determination unit EA, the differential calculation is performed on frequency demodulated signals I B a' and I B b' that include the influence of FM noise.

In this case, since the calculation result includes the possibility of malfunction, the circuit breaker is prevented from tripping by opening the contact Sw.

G is an auxiliary relay which inputs the demodulated signal Ip and opens the contact Sw when it is not a predetermined signal.

In the present invention, the constant value for the pilot signal is set to approximately zero, but by setting this to an appropriate level, disconnection of the communication line can be detected.

In other words, the loss of the pilot signal that is constantly being received is equivalent to the reception frequency becoming lower.

As described above, according to the present invention, F
M IJ tray malfunction can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a conventional FMIJ tray, FIG. 2 is a diagram specifically showing the state of modulation during signal transmission, and FIG. 3 is a schematic configuration diagram of an embodiment of the present invention. Figure 4 is a detailed diagram of the main part. MA, MB...Modulation section, DA, DB...
... Demodulator, RY... Protective relay device, EA.
...Relay determination unit, SF...Signal transmission device.

Claims (1)

[Claims] 1 Contains a first frequency modulation signal obtained by modulating a modulated wave of a predetermined frequency with a B-end electrical station current and a second frequency modulation signal obtained by modulating a modulated wave of a predetermined frequency with a pilot signal. A transmitter that multiplex modulates a plurality of frequency modulated signals and outputs a carrier wave, a receiver that receives the carrier wave and demodulates it to restore the plurality of frequency modulated signals, and is installed at an A-end electrical station of a power transmission line, a first demodulating means for demodulating a first frequency modulated signal obtained from the receiver; and an error occurring during signal transmission from the demodulated signal while demodulating a second frequency modulated signal obtained from the receiver. a second demodulating means for deriving only the signal; a relay determining section for adding the output of the first demodulating means and the A-end current of the power transmission line and giving a breaker pull-out signal according to the output after power calculation; , a protection relay device having signal blocking means for blocking a bow disconnection signal of a circuit breaker in a relay determination section when an error signal is obtained from the second demodulation means. A method to prevent malfunction of electrical equipment.