JPS6220769B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides power system current obtained from an electric station,
A relay that modulates a carrier wave (frequency modulation, amplitude modulation, etc.) with a signal such as voltage or a composite value of these, and transmits this modulated wave to each other to determine the fault section of the power system. Regarding the method. In the differential relay system, signals (for example, current waveforms) from each electrical station are sent and received to other electrical stations,
These signals are combined to determine the operation, and there are various methods for transmitting and receiving this signal. For example, there is a frequency modulation (hereinafter referred to as FM) transmission method as a means of transmitting analog waveforms that are resistant to noise.
Figure 1 shows an example of a differential relay system using the FM transmission system. In FIG. 1, reference numeral 11 denotes a current-to-frequency converter which generates a frequency proportional to the magnitude of the instantaneous value of the current extracted by the current transformer 18 at each electric station. In other words, it is a device that frequency modulates a carrier wave according to the magnitude of current. 12 is a transmitter of the communication set, which transmits the output of the converter 11. The FM wave from the transmitting section at the other end is received by the receiving section 19 of the communication set. 13 is a microwave line,
14 is a relay determination unit that determines whether the accident section is inside or outside by introducing the own terminal signal and other terminal signals;
15 indicates a bridge or disconnector, 16 indicates a power transmission line, and 17 indicates a bus bar.

This relay method focuses on the magnitude and phase of the current flowing through the current transformers 18A and 18B of electrical stations A and B, and determines whether the fault is within the protected area or outside the protected area. If an accident occurs, a trip command is issued to the shield disconnectors 15 at both ends of the protection zone to eliminate the accident. On the other hand, if it is outside the protected area, no trip command will be issued. Note that the letters A and B in the explanatory numerals above indicate those installed in each electrical station, for example, A indicates those installed in the A electrical station, and those with the same operating functions are designated by the same numbers.

In the protective relay system configured as described above, when a failure occurs in the communication units 12 and 13 or a decrease in the electric field strength of the communication line occurs, the signal S transmitted is
For example, as shown in FIG. 2, what should be a sine wave is distorted like N. The duration of such communication failures is not constant, and according to actual measurements, most cases last less than half a cycle. Note that the specific cause of this occurrence has not been determined. If such noise enters and the demodulated wave obtained from the receiving section 19 is disturbed, the input to each relay determination section 14 may be different from the current waveform detected at electric stations A and B. Depending on the noise level and duration, the relay may malfunction. Since such malfunctions cause serious damage to the power system and further degrade service to customers, it is necessary to prevent relays from malfunctioning due to such noise. In order to prevent this malfunction, it is necessary to use a noise-resistant determination method in the relay determining section, or to detect noise intrusion into the communication line and apply that signal to the relay determining section to lock the relay operation. On the other hand, for stable operation of the power system, there are problems such as the inability to apply the above-mentioned lock more than necessary, so it is necessary to emphasize both aspects.

The specific configuration of the circuit shown in FIG. 1 will be explained with reference to FIG.

11, 12, 13, 16, 18 in Figure 3
11' is the same as the reference numerals shown in FIG. 1, so the explanation will be omitted, but 11' is a delay unit for matching a signal from the own electric station, such as an FM signal, with the transmission delay time from the other end, and a frequency-voltage converter ( (hereinafter referred to as F-V)
This part obtains a commercial frequency signal of the detected current at its own end, and its output is supplied to the relay determination section 14'. The receiving unit 19 also connects to the microwave line 13, and communicates by observing the carrier wave or demodulated wave with a demodulating unit 29S that demodulates the signal, that is, performs F-V and derives the commercial frequency signal of the other end as 2S. A first noise detection means 29 that detects that noise has entered the line and derives the output signal 2N.
N, and a second noise detection means 20N that detects noise on the communication line through another channel of the circuit 13, such as a channel dedicated to noise detection, and obtains 2N'. In addition, OR is 29N each,
This is an OR circuit that outputs when there is an output on any of the 20N, and this is used as a lock signal. FIG. 4 is a diagram explaining the operating principle of the differential relay system. That is, 2SA and 2SB are signals obtained by transmitting or delaying and demodulating the current signals of each substation, and when these signals are applied to the input of the vector sum circuit 30 and the input of the scalar sum circuit 31, first the vector sum circuit 30 The output ΣI〓 is approximately "0" when there is no fault in the power system or when there is an external fault, but when an internal fault occurs, an output signal of a magnitude corresponding to the fault is obtained. Therefore, by monitoring the presence or absence of this output ΣI,
It is possible to determine whether an electrical system accident is internal or external.

On the other hand, the output Σ|I| of the scalar summation circuit 31 is the absolute value of the current at each end for the purpose of preventing the relay from malfunctioning due to the influence of distortion of the current transformer when a large current passes through the current transformer 18. The signals are derived and added to derive the passing current of the power system, and this signal is used as a suppression signal for the output of the vector sum circuit 30. Based on this vector sum and scalar sum, it is determined whether or not the operation is possible. The judgment operation mainly uses resistors R ₁ to R ₆ and
This is done using VR and operational amplifiers 43 and 44. That is, in order to derive the absolute value of the signal of the vector sum circuit 30, the rectifier D is used to rectify the signal, and a "-" signal is obtained at its output. The operational amplifier 43 calculates addition and subtraction between this signal and the suppression signal obtained from the scalar sum circuit 31, and the operational amplifier determines whether the calculated output is larger or smaller than the voltage obtained by dividing the reference voltage VRF by the variable resistor VR. 44, and when the calculation output is large, the relay operation output is generated from 44. The capacitor C in parallel with the resistor _R3 is used to adjust the operation and recovery times. On the other hand, when noise enters the communication line, etc., the signal 2N (or 2
When N') is applied, that signal is first applied via the resistor RN so that the operational output of the operational amplifier 43 becomes a disable signal. A lock signal is applied via a polarity inverting circuit 41 to an inhibit circuit 42 for blocking the relay operation determination output 45 on the other side. Note that the presence of a circle on one of the inputs of the inhibit circuit indicates that this terminal is an inhibit terminal, which means that when the output of circuit 41 is 0, the output of the inhibit circuit is set to 0. ing. Therefore, when noise is detected and the signal 2N becomes 1, the output of the polarity inversion circuit 41 becomes 0 and the output of the inhibit circuit becomes 0. The circuit 41 is used here only to match the polarity relationship in the circuit configuration, and is not an essential problem. In the operation judgment method using this arithmetic method, although it depends on the value of the capacitor C for adjusting the operation and recovery time, in general, if a demodulated waveform like N in Fig. 2 enters and no noise is detected, the operation will not work. Therefore, it can be said that this determination method has poor noise characteristics, that is, it is a relay determination method that is vulnerable to noise intrusion.

Figure 5 shows that even though the same currents I _A and I B are passing through electric stations A and _B , the current signal at the other end is affected as shown in Figure 2, resulting in a possibility of malfunction. FIG. The figure shows an example in which the current signal at the A end is correctly reproduced as 2SA, and the B end's 2SB is affected. As a result, the output ΣI〓 of the vector sum circuit 30 appears large even though it is originally "0". Therefore, it overcomes the scalar sum, which is a suppressing force, and produces a relay output after a time determined by capacitor C.

However, on the other hand, even when there is a large operating force as in the output ΣI of the vector sum circuit in Fig. 5, if the suppressing force is increased so that the relay does not operate, there is sufficient power even when the relay should operate. It will not work. That is, the detection sensitivity decreases, which is inconvenient. In view of the above, it is an object of the present invention to provide a differential protective relay system in which the protective relay itself is unlikely to malfunction due to noise, and will not malfunction even in the event of noise that cannot be dealt with by the protective relay itself. It is an object.

Therefore, the present invention focuses on the fact that the influence of noise, etc. extends to both positive and negative waves, and that it is unlikely to appear in the form of reversing the positive and negative waves over one cycle. This is intended to prevent malfunctions by performing operation determination independently for each positive and negative half-wave and outputting an output only when the determination outputs of each wave match. In the present invention, in order to realize this, the output of the vector sum circuit is divided into positive and negative, and it is determined whether the output is operational or not.

Embodiments of the relay determination section of the present invention will be described below.

In FIG. 6, 2SA and 2SB are demodulated waves of the current waveforms of each electrical station similar to those described above, and are input signal lines for relay determination. TA and TB are transformers for calculating the vector sum of 2SA and 2SB in order to determine internal and external accidents, and the combined output is applied to both ends of resistors R ₁₁ and R ₁₂ . The connection point between the resistors R ₁₁ and R ₁₂ is grounded, so that positive and negative voltages centering on the zero point of the vector sum ΣI〓 appear at the connection points 50 and 50'. On the other hand, the suppression circuit 31 also has 2SA,
2SB signals are added and a scalar sum is derived. In this embodiment, this scalar sum Σ|I| is applied to a circuit consisting of resistors R ₁₃ to R ₁₆ and an operational amplifier 59, and a voltage obtained by dividing the reference voltage VRF by a resistor VR is also applied to this circuit. Therefore, op amp 5
As the output of 9, the suppression amount is obtained as a voltage corrected by the partial voltage value of the reference voltage. That is, the sensitivity of the relay can be controlled by adjusting the VR.

52 and 52' are comparators, and the values of the positive and negative half-waves of the vector sum as the operating force obtained at the terminals 50 and 50', and the scalar sum obtained in the operational amplifier 59 as the suppressing force, which also takes into account the sensitivity. A comparison is made with the value. Here, 52 and 52' are assumed to produce a constant output when the respective values are larger than the output of the operational amplifier 59 during the period in which positive and negative waves appear as positive values at the terminals 50 and 50', respectively. Ru.

The outputs 52SA, 52SB of the comparators 52, 52' pass through the gates 54, 54' on the condition that there is no noise detection signal 2N or 2N'. Here, the gates 54, 54', 54D have the same inhibit function as in FIG. This means that the output of 54D is set to 0. Note that the reason why the polarity of the noise detection signal 2N or 2N' is inverted by the inverting circuit 41 is for the reason of the circuit configuration and is not an essential problem. 55,55'
is a timer consisting of, for example, an integrator and a level detector cascaded, and outputs 52SA,
An output is generated when 52SB continues over 90 degrees.
Flip-flop circuits 58 and 58' input the outputs of the timers 55' and 55' to a set terminal S, and are set when they are present, producing an output at an output terminal Q.

On the other hand, 56 is a NOR circuit, and comparators 52 and 5
When there is no output 52SA or 52SB of 2', the output 56S is present, and if there is an output to either one, there is no output. 57 is a timer, which produces an output when the output 56S of the NOR circuit 56 continues, for example, 90 degrees or more. The output of timer 57 is the reset terminal of flip-flops 58, 58'.
Added to RS. The flip-flop 58 has no output at its output terminal Q when there is an input at its reset terminal.

540 is an output gate and a noise detection signal 2N
Or, on the condition that 2N' is absent, an output is produced when there are outputs from both output terminals Q of flip-flops 58, 58'.

That is, in the present invention, the operating output can only be obtained when it is confirmed that the vector sum as the operating force is equal to or greater than the predetermined suppressing force for both the positive wave and the negative wave, as shown in FIG. It is now impossible for the system to malfunction due to such noise.

Of course, if the noise signal 2N or 2N' is obtained, the flip-flops 58 and 58' will be connected to the reset terminal RN.
Needless to say, the noise signal applied to the circuit immediately resets the circuit and prevents malfunctions.

7 and 8 are waveform diagrams for the embodiment of FIG. 6, respectively, for explaining the normal operation and prevention of malfunction according to the present invention.
The horizontal axis shows time, and the vertical axis shows the waveform of each part. Each part is indicated by the same reference numerals as in FIG. 6, and 0 indicates that there is no output or 0 level, and 1 indicates that there is an output. L is the determination level of each timer.

FIG. 7 shows an example in which the phase of the signal 2SB is reversed at time t ₀ due to an internal accident, and the output of the timer 55' is obtained at time t ₁ and the timer 55' at time _{t 2 .} The output is obtained.

FIG. 8 shows a case where the phase of signal 2SB is reversed over half a cycle due to noise at time _t3 .
Therefore, if no noise is detected, time t ₄
The output of the timer 55 is obtained at time t5, but since the output of the timer 57 is obtained at time _t5 , output to the signal line 60 is prevented. Of course, it goes without saying that if a noise signal is obtained, the output of the timer 55 can be prevented.

In addition, if the influence of noise appearing in 2SB in FIG. 8 causes a phase shift, for example, if the phase is shifted by 90 degrees, the vector sum ΣI will appear positive and negative, but the comparator 52's The output is
Since it will not last more than 90 degrees, both timers 5
5,55' will not produce any output.

This means that the operating sensitivity can be determined by the relationship between the output level of the suppressing force 59 and the time setting of the timers 55 and 55'. In other words, in order to make it difficult to malfunction due to noise, if the sensitivity is lowered, there is no problem even if the timer setting is short, but if the sensitivity is increased, the timer needs to be set at about 90 degrees. become.

In this embodiment, both the timer and the flip-flop are cleared by the noise detection signal, so when the noise detection signal disappears, the determination of whether or not the operation is necessary is restarted from the beginning. No unnecessary malfunctions will be induced.

Furthermore, in the embodiment shown in FIG. 6, the reason why the vector sum circuit 30 and the scalar sum circuit 31 are indicated by X is to explain an example in which this embodiment is applied to a multi-terminal power transmission system having three or more terminals. Although not shown,
For example, if there are 3 terminals, the signal 2 for the other terminal
SC will be introduced. In that case, the vector sum circuit may be provided with a transformer TC, whose secondary winding is opened at the point X and connected therebetween, and the signal 2SC is introduced into the point X in the scalar sum circuit 31.

FIG. 9 shows another embodiment in which the output portion of FIG. 6 is modified. This embodiment converts the outputs of the timers 55, 55' into analog pulse serialization circuits 70, 7.
0', the rest is substantially the same. Since the circuits 70 and 70' make the outputs of the timers 55 and 55' continuous on the condition that there is no noise signal 2N or 2N', once there is an input, an output that continues for at least 180 degrees is produced, but the noise signal If 2N or 2N' is present, the output is immediately extinguished. Of course, when there is a noise signal 2N or 2N', the gate 5
4, 54' is blocked, and the timer 55, 5' is blocked.
Needless to say, 5' will be reinstated.

Furthermore, it goes without saying that various modifications can be made in carrying out the present invention. For example, the operating force and the restraining force may be combined, separated into positive and negative waves, and then made into a rectangular wave.

In summary, the present invention separates the vector sum signal, which is the operating force, into positive and negative waves, and obtains the operating output only when both of these waves meet the operating conditions. This makes it possible to prevent unnecessary malfunctions and almost eliminate 1
It is possible to realize a relay that can obtain operating signals in cycles. According to the present invention, the protective relay itself is unlikely to malfunction due to noise. In other words, since some types of noise superimposed on the communication line are less than half a cycle and occur only in either the positive or negative waveforms, it is determined that both the positive and negative waveforms have a predetermined width or more. This makes the protective relay itself less likely to malfunction due to noise.

However, some noises do not only have such characteristics, and some noises cannot be dealt with by determining that both positive and negative waveforms have a predetermined width or more.
It is necessary to provide a separate noise detection means and use its output to block the protective relay output.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the concept of a transport protection relay device, Fig. 2 is a diagram to explain changes in waveform due to the influence of noise, and Fig. 3 is a diagram showing the concept of the conveyance protection relay device. Figure 4 is a diagram explaining the operation of a differential relay, and Figure 5 is a diagram showing the operation of a differential relay.
6 is a diagram illustrating an embodiment of the present invention, FIGS. 7 and 8 are waveform diagrams illustrating the operation of the embodiment of the present invention, and FIG. 9 is a diagram illustrating the malfunction of the relay shown in FIG. FIG. 7 is a diagram showing another embodiment of the invention. Explanation of symbols, 11...Current-frequency converter, 1
2... Transmission unit, 13... Microwave line, 14...
... Relay determination section, 19 ... Receiving section, 30 ... Vector sum circuit, 31 ... Scalar sum circuit, 52 ...
Comparison circuit, 54...gate, 55...timer,
58...flipflop, 540...gate.

Claims (1)

[Scope of Claims] 1. A first means for inputting the amount of alternating current at the own end of the power transmission line, a second means for inputting the amount of alternating current at the opposite end of the power transmission line, and a carrier wave with the amount of alternating current input by the second means. a third means for modulating the signal, a fourth means for transmitting the signal modulated by the third means to the own end, and an alternating current amount input by receiving and demodulating the signal transmitted by the fourth means. a sixth means for deriving the vector sum of the output of the first means and the output of the fifth means;
a seventh means for deriving a scalar sum of the output of the first means and the output of the fifth means; an output of the sixth means using the scalar sum which is the output of the seventh means as a reference value; an eighth means for deriving a rectangular wave output for each positive wave and negative wave of the vector sum, the width of the rectangular wave output for each positive wave and negative wave of the vector sum obtained by the eighth means are both a predetermined width; and a ninth means for outputting when the above is satisfied. 2. In the differential current protection relay system according to claim 1, tenth means detects noise included in the signal transmitted by the fourth means and stops the operation of the ninth means. A differential current protection relay system characterized by: