JPS6129216B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a multi-terminal differential protection relay device in which a protected system attempts differential protection by transmitting each terminal current to all other terminals, especially in power transmission protection, etc. The present invention relates to an abnormality detection device.

In recent years, due to the need to increase power demand, ultra-high voltage power transmission lines are often made into three-terminal systems. Comparative carrier protection relay systems have limits to their protection capabilities.

For this reason, attention is being paid to the application of a current differential transfer protection system that provides reliable protection under any system conditions.

As is well known, when applying the current differential method to protection of power transmission lines where the terminals are separated from each other, it is necessary to transmit the current from each terminal to all other terminals, and it is necessary to transmit the current from each terminal to all the other terminals. It depends on the means of

Therefore, current differential means a circuit that converts current into voltage, a modulation circuit that modulates voltage to make it suitable for transmission, a transmission line, and a circuit that receives the transmitted waveform and converts it to the original waveform. A large number of extremely complex circuits are inserted in the middle, such as a demodulation circuit for reproduction and a differential protection circuit for differential protection from the demodulated waveform, so even if a problem occurs in any part of these circuits, It is not possible to reproduce faithful waveforms, and since the transmission line is generally exposed to the air, it is susceptible to disturbances such as noise, so there is a possibility of erroneous judgments when implementing differential protection. comes out.

In order to prevent misjudgments due to the above causes and realize a highly reliable multi-terminal differential protection relay device, the present invention provides a combination of the current vector sum of each phase sent from the terminal and demodulated, and the Detect abnormal phenomena including the transmission line by sending the zero-phase current from the same as for each phase, demodulating it to create a zero-phase current vector, and comparing it with the sum of the current vectors of each phase. This is what we propose.

For convenience of explanation, both the conventional abnormality detection method and the embodiment of the abnormality detection method according to the present invention are two-terminal power transmission lines, and the transmission method uses frequency modulation (hereinafter referred to as FM modulation) to prevent noise from entering the transmission path. Let's explain the case.

Figure 1 shows one phase in order to explain the circuit configuration principle of differential protection using the FM scheme applied to two-terminal power transmission line protection at ends A and B. is a circuit breaker (hereinafter referred to as CB), 2,
12 is a CT; 3 and 13 are IV converters that convert the CT secondary current into voltage to make it easier to process; 4 and 14
V-F converters 5 and 15, which convert the instantaneous value of voltage into a frequency for transmission, are transmitting sections, and transmit FM-modulated signals to other terminals;
Reference numeral 16 designates a receiving section for receiving signals from other terminals, and reference numerals 7 and 17 designate FV converters that convert the magnitude of the reception frequency into an instantaneous value of voltage. 8 and 18 are differential protection circuits that perform differential protection by inputting the voltage values of the IV converters 3 and 13 and the voltage values of the FV converters 7 and 17; Based on the judgment of the circuit, it is output when a system fault occurs between terminals A and B, and outputs CB1 and CB1 respectively.
1 to stop power transmission.

Figures 2 and 3 are explanatory diagrams of the operation of the device shown in Figure 1. Figure 2 explains the principle of differential protection against an external accident X in the system, and Figure 3 explains the principle of differential protection against an internal accident Y. .

In FIG. 1, if an external fault occurs at point X, the fault currents flowing through CTs 1 and 11 have opposite polarities and become penetrating currents.

Figure 2a shows this current, with terminal A and terminal B
They are out of phase at the ends. b is the IV converter 3,
13, and this output is obtained from the FM-modulated output VF converters 4 and 14 as shown in c. That is, when the waveform is large, the frequency is controlled to be high, and when the waveform is small, the frequency is controlled to be low.

These FM modulated waves are mutually received as shown in d and demodulated by F-V converters 7 and 17 to return to voltage as shown in e. f and g indicate the internal states of the differential protection circuits 8 and 18;
The sum of g forms the operating force, and the subtraction of b and e forms the restraining force.

Therefore, in FIG. 2, the operating force is zero at both the A terminal and the B terminal, and only the suppressing force exists, so that no output is output from the differential protection circuit. Therefore, CB will not be opened.

FIG. 3 is an explanatory diagram when an internal fault occurs at point Y in FIG. 1, and the fault current at end B clearly goes in the opposite direction to the fault at point X. Therefore, in Fig. 3, compared to Fig. 2, a, b, c at the B end, d at the A end,
Since e is in the opposite phase, the operating force of the differential protection circuit is outputted by adding b and e and becomes f, and the suppressing force is reduced by subtracting b and e, as shown in g.

Therefore, in Figure 3, only the operating force exists at both ends A and B, and the suppressing force is zero, so an output is output from the differential protection circuit and CB1 and 11 at both ends are opened. .

Although FIG. 1 illustrates the principle configuration using a single line diagram, when the system is differentially protected, the currents at both ends are compared for each phase, so the configuration is as shown in FIG. 4. This figure 4 shows the conventional configuration of a differential protection relay, and shows the case where current is transmitted from the A terminal to the B terminal, and the same applies when transmitting current from the B terminal to the A terminal. be.

First, at the A terminal, 2a to 2c are CT to increase the secondary current by 3.
A voltage is obtained by passing it through the IV converters shown as a to 3c, and FM modulation is performed by the VF converter shown as 4a to 4c.
The outputs of these phases are transmitted to the B end by transmitters 5a to 5c.

At the B end, this transmission is received by the receivers 16a to 16c, demodulated by the F-V converters 17a to 17c, and used as one input of the differential protection circuits 18a to 18c. Differential protection is performed using the other input voltages Va, Vb, and Vc.

If the system fault is internal, the output signal of this differential protection circuit will be routed through the inhibit circuit 22 to the B terminal.
The signal is sent to the CB (not shown), and the CB is released.

If noise were to enter the transmission path now, the signal would be erroneously transmitted at the B end, causing all or part of the -V converters 17a to 17c to output incorrectly, and the differential protection circuits 18a to All or part of 18c may issue an error or a disconnection signal, which poses a problem both when the system is healthy and when an external accident occurs.

Therefore, as a countermeasure, it is common practice to detect the intrusion of noise and lock the interruption.

If an oscillator 20 with a constant frequency F _o is installed at the A end and the transmitter S _o transmits to the B end, the receiver 16n at the B end receives the constant frequency. F this
- If the voltage is converted to voltage by the V converter 17n, a constant voltage of V _o can be obtained. If noise N ₂ enters the transmission path, the receiving frequency will no longer be constant, and the output of the F-V converter 17n will be V ₂ The output can be detected by the detector 21. Therefore, by locking the signals of the differential protection circuits 18a to 18c with the inhibit circuit 22 when the output of the detector 21 is output, CB errors and disconnections can be prevented.

Figure 5 is for explaining the situation when noise enters a constant frequency F _o , where A is the frequency -
This shows the voltage conversion characteristics, and when F _o, the voltage of V _o is obtained, but when it becomes F ₂ , it becomes V ₂ , and when it becomes F 1, it becomes _{V 1 .} B is a time chart, and d is a constant frequency (period t), when noise N ₂ enters and the period becomes dense, and when the noise is opposite in magnitude.
This shows the case where N ₁ enters and the period becomes coarse, and the F-V converter outputs as shown in e. This is detected at the detector level (LD ₂ or LD ₁ ),
An output h can be obtained.

Therefore, the above-mentioned inhibit circuit was limited by the signal shown in h.

In this way, the conventional noise detection method installs a noise detection phase separately from each phase, sends a signal with a constant frequency on the transmission path, demodulates this on the receiving side to obtain a constant voltage, When noise invades, it is detected by using changes in the demodulated voltage.

In such conventional methods, the transmission paths for each phase and the noise detection phase are separate, so noise enters only the transmission path of each phase, for example, the A phase, and is transmitted to the B phase, C phase, and the noise detection phase. Noise detection is impossible without intrusion,
There was a possibility of making a mistake or making a mistake.

In addition to the noise that invades the transmission path, the I-V converters 3a to 3c, V-F converters 4a to 4c, transmitters 5a5e, and receivers 16a to 16a of each phase shown in FIG.
16c and any of the F-V converters 17a to 17e becomes abnormal, the principle of differential protection no longer holds true, and there is a possibility of an error or disconnection.

This invention was made in view of these circumstances, and in addition to each phase current, zero-phase current is also transmitted,
By calculating the sum on the receiving side, if there is no noise intrusion or circuit abnormality, the sum is always zero, and if noise intrusion or circuit abnormality occurs, the sum is not zero. This paper proposes a method for detecting

Examples of the present invention will be described below.

That is, in FIG. 6, an IV converter 30 is installed in the CT second-order zero-phase current circuit at the A terminal, and its output voltage is input to a V-F converter 40 for FM modulation. The transmitter 50 transmits the signal to the B end.

At the B end, the receiver 160 receives this and sends it to the F-
The V converter 170 demodulates it into a voltage.

These IV converters for zero-phase current transmission V-
The F converter, transmitter, receiver, and F-V converter are the same for each phase. The voltage demodulated by the FV converter 170 is sent to the sign inverter 23 and its polarity is reversed.

On the other hand, the voltage of each phase obtained by demodulating each phase current is provided to the differential protection circuits 18a to 18c of each phase, and at the same time, is provided as an input to the summation circuit 24. The sum of this and the output of the sign inverter 23 is obtained and sent to the detector 21. If the sum exceeds the set value, a signal is sent to the inhibit circuit 22, and from the differential protection circuits 18a to 18c, Locks the break signal to the B end CB (not shown). Although not shown, a completely similar circuit configuration is provided from the B end to the A end.

Now, at the A terminal, each phase current is Ia, Ib, Ic, and zero phase current is
If 3I ₀ , the relationship 3I ₀ = Ia + Ib + Ic will always hold whether the system is normal or there is a system fault, so this is transmitted to the B terminal and the voltage obtained by demodulating is Ia → V′a, Ib→V′b, Ic→V′c, 3I ₀ →
If 3V′ ₀ , then the relationship 3V′ ₀ =V′a+V′b+V′c always holds true.

The output obtained by applying 3V' ₀ to the sign inverter 23 is -3V' ₀ , so the input of the summation circuit 24 is Σ=Va'+Vb'+Vc'-3I ₀ ', and if there is no noise intrusion, the circuit If is normal, Σ
=0.

If noise enters any of the four transmission paths or the circuit becomes abnormal, Σ≠0, an output is output from the summation circuit 24, and can be detected by the detector 21.

FIG. 7 is a time chart explaining the operating state of the present invention. (A) is when the system is normal and there is no noise intrusion and the circuit is normal, (B) and (C) are when there is only one line in the system. When a ground fault occurs, (b) shows a case where there is no noise intrusion and the circuit is normal, and (c) shows a case where noise intrudes only into the a phase but the circuit is abnormal.

The waveform shown in (e) of (a) is the demodulated waveform, Va′, Vb′,
Vc′, 3V ₀ ′ and the system is normal, so 3V ₀ ′=0
It is.

(j) shows the output Σ of the summation circuit, which becomes zero, and therefore the output of the detector shown in (k) also becomes zero.

(b) is a one-wire ground fault, and the a-phase waveform Va′ is a zero-phase waveform.
Since it is the same as 3V ₀ ′ and Σ=Va′−3V ₀ ′=0, both (j) and (k) are zero.

(C) shows the case where the dotted line portion of Va' is not demodulated due to noise entering the a phase of the single-wire ground fault or the circuit becoming abnormal; in this case, Σ=Va'-
3V ₀ '≠0, and as shown in (j), the output appears by the amount of the error and exceeds the detection level LD, (k)
The output shown is obtained. By inputting this output to the inhibit circuit and blocking the failure signal from the differential circuit, it is possible to lock out errors and disconnections in the event of an external fault.

In addition, in the above embodiment, as shown in FIG.
Zero-phase IV converter 3 to obtain zero-phase current component
0, but if the occurrence of abnormalities in the IV converters 3a to 3c of each phase can be ignored,
It is also possible to omit the zero-phase IV converter 30 and provide an adder circuit 31 for synthesizing the output voltages of the IV converters 3a to 3c of each phase, as shown in FIG. It is obvious that the output of this adder circuit 31 is proportional to the zero-phase current component. In this case, it is naturally impossible to detect an abnormality in the IV converters 3a to 3c of each phase, but the VF converters 4a to 4c and the transmitter 5 connected after that cannot be detected.
It is possible to detect abnormalities in the transmitters a to 5c, receivers 16a to 16c, and FV converters 17a to 17c, as well as noise entering the transmission path.

In the event of an internal accident, this lock becomes a failure lock, slowing down the failure time, and this is the same in the conventional system.

In the above embodiment, it was explained that the sign of 3V ₀ ' is inverted and the sum of the demodulated waves of each phase current is calculated. (take the difference). Further, in the above embodiments, a two-terminal system was described, but three or more terminals may be used.

In the above embodiment, there are a total of four transmission lines, one for each phase current and one for the zero-phase current.
I explained that the current is transmitted simultaneously in parallel, but
Even if the method shown in Fig. 8 uses digital transmission using PCM etc., the transmission path is one line, and each phase current and zero-phase current are transmitted temporally divided.
It may be a method of temporally storing frames and comparing the sum component of each phase current with the zero-sequence current component.

As mentioned above, the abnormality detection device for the differential protection relay device according to the present invention utilizes the principle that the sum of the phase currents and the zero-sequence current are always equal regardless of the system status, so that abnormalities can be detected. This has the effect of ensuring reliable detection even when it occurs only in a specific phase.

Furthermore, since the zero-phase current is transmitted using exactly the same circuit system as the transmission of each phase current, variations due to changes in circuit constants, etc. are the same for each phase and are canceled out, resulting in little variation in detection sensitivity.

[Brief explanation of the drawing]

Figure 1 is a circuit configuration diagram of differential protection for a two-terminal power transmission line, Figures 2 and 3 are diagrams explaining its operation, and Figure 4 is a circuit configuration showing the noise detection method of a conventional differential protection relay. Figure 5 is a diagram explaining the conventional noise detection method, Figures 6 and 9 are circuit configuration diagrams showing the noise detection method of the differential protection relay according to the present invention, and Figure 7 is the noise detection method according to the present invention. Figure 8, which is a diagram explaining the method, is a diagram showing a transmission form in which the transmission line is one line, and in the diagram, 1, 11, 1a to 1c are circuit breakers,
2, 12, 2a ~ 2c are CT, 3, 13, 3a ~
3c, 30 are IV converters, 4, 14, 4a-4
c, 40 are V-F converters, 5, 15, 5a-5
c, 50, 5n are transmitters, 6, 16, 16a-1
6c, 160, 16n are receivers, 7, 17, 17
a to 17c, 170, 17n are F-V converters,
8, 18, 18a to 18c are differential protection circuits, 9 is a protected transmission line, 20 is an oscillator, 21 is a detector, 2
2 is an inhibit circuit, 23 is a sign inversion circuit, 2
4, the summation circuit 31 is an addition circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In an abnormality detection device for a differential protection relay device that transmits the current of each phase of one terminal of the protected system to all other terminals and provides differential protection for each phase, the current of each phase of the terminal is detected. A signal transmission path that transmits the zero-sequence current of the terminal is provided in the signal transmission path that transmits the current, and after transmission through this signal transmission path, the sum of each phase of the demodulated phase current and the zero-sequence current are calculated. 1. An abnormality detection device for a differential protective relay device, characterized in that an abnormality in the differential protective relay device is detected by determining the presence or absence of a difference between the two.