JPH053206B2 - - Google Patents

Abstract

1. A current-interruption arrangement, preferably short-circuit currents, in three-phase networks (R, S, T), wherein the current of one phase (T) does not pass through zero initially, separate switches being controlled by a current detection device (3-8) having zero current transit detection devices (3) for the phases, characterised in that the current detection device (3-8) in each case detects that (S) of the phases (R, S) passing through zero, wherein the difference of the adjacent time intervals (C-D, D-G) defined by three consecutive zero transitions (C, D, G) is greater than in the case of the other phase (R) and the phase (S), in which the difference is greater, interrupts first.

Description

[Detailed Description of the Invention] [Technical Field to Which the Invention Pertains] This invention relates to a three-phase circuit having a waveform in which the short-circuit current of any one of the three phases does not pass through a zero point within a predetermined time period in which the short-circuit current of any one of the three phases is to be cut off. The present invention relates to a method for interrupting short-circuit current using an ordinary AC circuit breaker or a semiconductor circuit breaker for AC circuits.

[Prior art and its problems]

Conventionally, as a method for interrupting short-circuit current that does not pass through the zero point using an AC circuit breaker, there are two methods: superimposing a high-frequency oscillating current on this short-circuit current to forcibly create a zero point and interrupting the current, and another method that uses an AC circuit breaker to interrupt the short-circuit current that does not pass through the zero point. Therefore, a method is known in which the direct current component of this short circuit current is rapidly attenuated to form a waveform that passes through a zero point, and the waveform is cut off at that zero point. Of these methods,
In the former method of superimposing oscillating current, a large number of capacitors are used as sources of oscillating current, a high-voltage step-up transformer for pre-charging the capacitors, a high-voltage rectifier, a reactor, a discharge device, its control device, etc. The economic burden is extremely heavy. Furthermore, the method of creating a current zero point using arc resistance in the circuit breaker has the drawback that it cannot be applied to devices such as semiconductor circuit breakers, which have a small forward voltage drop.

Therefore, as a breaking method that can be applied to semiconductor circuit breakers with a small economic burden and a small forward voltage drop, by first cutting off the current that does not pass through the zero point and the current that does not intersect, the current that does not pass through the zero point becomes the zero point. Focusing on the fact that the current in the remaining one phase, which was passing through the zero point, does not stop passing through the zero point, there is a method of first cutting off the current that does not pass through the zero point and the current that does not intersect. It has been proposed (Japanese Patent Application No. 58-20503). However, in this method, in order to detect the first phase to be cut off, in addition to detecting whether the current of each phase passes through the zero point, it is also necessary to detect whether the currents of two phases cross each other. For this reason, for example, a three-phase current transformer is required to obtain a current waveform to be input to the detection device, so there remains a point to be improved in terms of economy.

[Purpose of the invention]

It is an object of the present invention to provide a breaking method that eliminates the above-mentioned conventional drawbacks, is more economical, and is universally applicable regardless of the magnitude of the arc resistance of the circuit breaker.

[Key points of the invention]

In this invention, among the two phase currents passing through the zero point, the current of the phase with the larger absolute value of the difference in the interval between adjacent zero points is cut off first, so that the current of the remaining two phases passes the zero point. This was done with a focus on the ability to pass through. As a result, during the predetermined period of time to be cut off, the short circuit current of one phase that does not pass through the zero point will pass through the zero point, and the phase that was passing through the zero point will not stop passing through the zero point, so the cutoff will occur. This makes it possible to universally apply AC circuit breakers regardless of the magnitude of the arc resistance of the device, and the phase to be shut off is first detected only by measuring the interval between the zero points of each phase current and comparing their magnitudes. , eliminating the need for detection across two phases, such as detecting the presence or absence of two-phase current crossings.
This is an attempt to further improve the economic efficiency of the shutoff method.

[Embodiments of the invention]

FIG. 1 shows an example of the waveform of a three-phase short-circuit current when a short-circuit current that does not pass through the zero point flows through the T phase. In the figure, the R-phase current passes through zero points at times A, B, E, F, etc., and the S-phase current passes at times C, F, etc.
It passes through the zero point at D, G, H, etc. Here, the difference between the interval between times A and B and the interval between times B and E is smaller than the difference between the interval between times C and D and the interval between D and G. In this way, when interrupting a three-phase short-circuit current, if the current of the phase with the smaller absolute value of the difference in the spacing between adjacent zero points, that is, the R phase, is interrupted at its first zero point A, the initial The S-phase current that had a zero point becomes a current without a zero point,
Both the S and T phase currents no longer pass through the zero point.
FIG. 3 shows the case where the R-phase current is first cut off at its second zero point B, similar to FIG. 2. In this case, as in FIG. 2, no zero point occurs in the S and T phase currents.

Therefore, as shown in Fig. 4, if the current in the phase with the larger absolute value of the difference in the spacing between adjacent zero points, that is, the S phase, is first interrupted at its first zero point C, the current in the remaining two phases, that is, the R and T phases, is cut off at its first zero point C. Both currents have waveforms that pass through the zero point. FIG. 5 shows the case where the S-phase current is first interrupted at its second zero point D, similar to FIG. 4. In this case, as in FIG. 4, the R and T phase currents pass through the zero point. In this way, by first interrupting the short-circuit current of the phase with the larger absolute value of the difference in the spacing between adjacent zero points, the three-phase short-circuit current that has a short-circuit current without a zero point in one of the phases can be converted into a normal alternating current. It was found that the circuit breaker or the semiconductor circuit breaker for AC circuits can be used to interrupt the operation. Therefore, by applying such a breaking method, it is possible to very economically cut off short-circuit currents without zero points, which have recently become a problem in large-capacity power generation and substations.

The above-mentioned detection of the phase to be cut off first can be performed, for example, by the following method.

FIG. 6 is a block diagram for explaining a method for detecting the phase in which the absolute value of the difference between the intervals between adjacent zero points in each phase current is maximum, and FIG. 7 shows an example of the detection means circuit. .

Current transformer 2 installed in each phase of main circuit 1 in Fig. 6
The zero point detection means 3 for the secondary current is as follows. The secondary current is rectified by the anti-parallel diode 31 of the zero point detection circuit 3 shown in FIG.
3 to generate a charging voltage V _C , and when the value near the zero point of the voltage V _R converted by the resistor 34 and the value of V _C match, the pulse transformer 35 becomes conductive and generates a voltage at the gate of the thyristor 36. occurs, and the zero point is detected by generating a pulse signal at V _P corresponding to the first zero point of the secondary current.

By repeating such an operation, each zero point of the secondary current is sequentially detected, and the difference in the spacing between zero points of the detected phases is determined using the following zero point spacing detection means.

The pulse signal _t1 corresponding to the first zero point causes the switching element 42 to conduct to the capacitor of the first integrator 4, which is composed of a resistor and a capacitor, of the zero-point interval detection circuit shown in FIG. It is charged from a voltage DC power source 41. In this case, when the switching element 42 becomes conductive, the switching element 43 becomes conductive with a time constant determined by the resistance capacitor. Next, the switching element 44 is made conductive by the pulse signal _t2 of the second zero point obtained from the zero point detection means 3 in the same manner, and the charging voltage of the first integrator 4 is discharged. Stop the operation of 4. In this case, the first integrator 4
The charging voltage of the capacitor during operation shows a voltage waveform with a maximum value V ₁ as shown in FIG.

Further, since the switching element 45 is also made conductive at the same time by the second zero point pulse signal _t2 , the capacitor constituting the second integrator 5 is charged by the constant voltage DC power supply 41. Further, when switching element 45 becomes conductive, switching element 46 becomes conductive. Next, the switching element 47 is brought into conduction by the pulse signal _t3 at the third zero point, and the operation of the second integrator 5 is stopped. In this case as well, as shown in FIG. 8, the charging voltage during operation of the second integrator 5 shows a voltage waveform having a maximum value _V2 .

The charging voltages V 1 and V ₂ charged to the respective capacitors of the first integrator ₄ and the second integrator 5 are:
As shown in Fig. 8, the longer the interval between zero points, the higher the value, so these charging voltages V ₁ and V ₂ are input to a subtracter 6 using an operational amplifier, and the difference is used to calculate the difference between adjacent zero points in that phase. interval (t ₂ −t ₁ ) and (t ₃
−t ₂ ) can be calculated. By calculating the difference in the interval between zero points in each phase and inputting it to the comparator 8 via an absolute value circuit 7 using an operational amplifier to calculate the absolute value of these values,
It is possible to detect the phase with the largest interval between zeros, that is, the phase that should be shut off first. In this case, since there is no output from the zero point detecting means 3 for a current having no zero point, the input to the comparator 8 is also 0, and the difference in interval between zero points is also assumed to be zero and is compared with other phases. Therefore, this phase will not be detected as the first phase of interruption.

After the phase to be cut off first is detected in this way, an example of a method for controlling the cutoff operation so that current is cut off first in this phase as the first cutoff phase will be described below.

FIG. 9 is a block diagram showing this control method, in which each phase of the main circuit 1 is provided with a current transformer 2 as an input device for detecting the first phase being cut off as described above. The secondary current is input to the first phase determining means 9 which detects the first phase being cut off.
This initial phase discriminating means 9 consists of 3 to 8 in FIG. 6 mentioned above. On the other hand, the output from the protective relay 10, which outputs a cut-off command based on the short-circuit current of the main circuit 1, enters an AND circuit 11, which will be described below.

As is well known, in a normal AC breaker,
There is a minimum arcing time necessary to interrupt the short-circuit current, and if a time longer than this arcing time has elapsed, the short-circuit current can be interrupted at any point where the zero point occurs. Therefore, after the first phase to be shut off, that is, the S phase, is detected at time G in FIG. 10 (an extension of the time axis in FIG. 1), this next small loop, that is, between times M and N By giving the interrupting command to the circuit breaker so that the position of the minimum arc time is on the peak value of , the S-phase short-circuit current is reliably interrupted first at time N. The position of this cutoff command can be determined using only the waveform of the AC component, regardless of the magnitude of the DC component, since the position of the minimum arc time is on the peak value of the AC component in the S-phase short circuit current. .
That is, in Fig. 10, the position P of the first peak value after the S-phase current is detected is detected using, for example, a differential circuit consisting of a resistor and a capacitor, and a cutoff command is issued after a certain period of time has elapsed from this position. In this case, the position of the minimum arc time may be placed on the peak value between the above-mentioned times M and N.

12 in FIG. 9 is the current transformer 2 of the phase to be cut off first among the current transformers 17 provided in each phase of the main circuit 1.
A phase selection means for passing only the next-side current,
An instruction as to which phase should be selected is given from the initial phase determining means 9. Further, 13 is means for detecting the position of the peak value of the current of the selected phase, that is, the peak point. The signal at this peak point of the phase that is first blocked,
The result of the AND with the three-phase cutoff command from the protective relay 10 is output from 11, and this output signal is output from 14.
When the tripping coil of the circuit breaker is reached after a predetermined time delay, the current of the phase to be interrupted first is interrupted first. If the circuit breaker is operated in three phases by one common operating device, please refer to the following 2.
When the phase current passes through the zero value, it is cut off at that zero value. If the circuit breaker is constructed such that each phase is driven to open and close independently by an operating device provided for each phase, the output from the delay means 14 that provides a time delay is delayed by about 0.5 cycles. The three-phase short-circuit current can be interrupted by leading to the delay means 15 to interrupt the other two phases after a delay of this time from the first phase to be interrupted. Note that the A contact of the auxiliary contact of the phase that was cut off first is opened with the breaking operation of the circuit breaker body, and the current in the tripping coil connected in series with this A contact is also cut off. Even if the shutdown command transmitted to the circuit breaker is for three phases, the shutdown command will not be transmitted again to the tripping coil of the phase that was shut off first.

〔Effect of the invention〕

When interrupting a three-phase short-circuit current in which the short-circuit current of any one phase does not pass through the zero point, the current of the two phases passing through the zero point, whichever has the larger absolute value of the difference in interval between adjacent zero points, By first interrupting the phase current, a zero point is naturally created in the remaining two phase currents, so it is universally applicable regardless of the magnitude of the arc voltage or the voltage drop in the circuit breaker. First, the phase to be shut off is first detected only by measuring the interval between the zero points of each phase current and comparing their magnitudes. Since it is unnecessary, for example, the current transformer required for this can be saved, and the economical efficiency of the interrupting method can be further improved.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of the waveform of a three-phase short-circuit current when the T-phase short-circuit current does not pass through the zero point, and Figure 2 shows the interval between adjacent zero points of the two phase currents that pass through the zero point. When the current of the phase with the smaller absolute value of the difference, that is, the R phase, is interrupted at its first zero point A, the current waveforms of the remaining two phases change after the interruption. Figure 3 shows the current of the R phase as well. its second zero point B
Figure 4 shows the changes in the current waveforms of the remaining two phases after the interruption when the current is interrupted for the first time. Figure 5 shows the changes in the current waveforms of the remaining two phases after the interruption when the current is first interrupted at C.
Figure 6 shows the changes in the current waveforms of the remaining two phases after the first shutdown in , and the method for detecting the phase where the absolute value of the difference in the interval between adjacent zero points in each phase current is maximum. FIG. 7 is a block diagram showing a specific example of detection in FIG. 6, and FIG.
The figure is a waveform diagram of the main part in Figure 7, and Figure 9 is a method of controlling the interrupting operation so that after the first phase to be interrupted is detected, that phase is the first phase to be interrupted and the current is interrupted first. FIG. 10 is an extension of the time axis of FIG. 1.

Claims (1)

[Claims] 1. A method for interrupting a three-phase short-circuit current in which the short-circuit current of any one of the three phases does not pass through the zero point, comprising a zero-point detection means for detecting the zero point of the short-circuit current of each phase, and a zero-point detection means for detecting the zero point of the short-circuit current of each phase. Inter-zero interval detection means for determining the absolute value of the difference in inter-zero interval between the zero point of the short-circuit current of each phase and the adjacent zero points of each subsequent phase; It consists of a comparison means for comparing the magnitude of the absolute value of the difference in the interval between two adjacent zero points in two passing phases, and the phase with the maximum difference in the interval between zero points obtained by this comparison means is A method for interrupting a three-phase short-circuit current, characterized in that the phase is the first phase to be interrupted.