JPH0130366B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a short-term power outage prevention device that prevents a short-term power outage in the event of a successful reclosing ground fault.

Conventionally, the method shown in FIG. 1, for example, has been generally used to protect against ground faults in ungrounded three-phase three-wire power distribution lines. In Figure 1, 1 is a three-phase AC power supply, 2 is a three-phase distribution line connected to this three-phase AC power supply 1, 3 is a voltage transformer for detecting zero-phase voltage, and 4 is a voltage transformer for detecting zero-phase voltage. ground fault relay,
5 is a switch, 6 is the ground capacitance of the three-phase distribution line 2, and 7 is a gap-shaped ground fault point assumed to be in the three-phase distribution line 2.

Next, the operation will be explained. In the configuration shown in FIG. 1, the vector diagram of the three-phase AC when the switch 5 is in the closed state is as shown in FIG.
e _a , e _b , e _c are the power supply voltages of the three-phase AC power supply 1,
If the power supply voltage peak value is E and the a phase is taken as a reference, it can be expressed as follows.

e _a = Esinωt e _b = Esin (ωt-2/3π) e _c Esin (ωt-4/3π) There is no ground fault on the line, and the ground capacitance of the line is 6
When all phases are balanced at C ₀ , no zero-phase voltage is generated, and the above power supply voltages e _a , e _b , and e _c are applied to the three-phase distribution line 2 as balanced three-phase voltages.

Here, for example, as shown in FIG. 1, when the a-phase gap-shaped ground fault point 7 discharges and causes a ground fault with a resistance value R _g , the following zero-sequence voltage V ₀ is generated.

V ₀ =−V ₀・sin(ωt−θ) However, Considering this condition using the vector diagram in Figure 2, the ground voltage at the neutral point moves from point O to O' due to the zero-sequence voltage V ₀ generated by the ground fault, and the ground voltage of each phase after the ground fault moves from point O to O'. The voltage to ground is expressed as V _a , V _b , and V _c . In this case, when the ground capacitance 6 and ground fault resistance of the line change, point O' moves on the circle diagram 8.

Generally, in order to protect against ground faults on power distribution lines, a method is adopted in which the switch 5 is opened by a signal from the ground fault relay 4, which is activated when the zero-sequence voltage exceeds a certain set level. After a short circuit accident, the switch 5 is opened after a certain set operating time, for example, about 20 cycles, and the line is placed in a voltage-free state. This operation time limit is intended to prevent unnecessary operations due to instantaneous ground faults.

On the other hand, ground faults in power distribution lines rarely occur permanently, and in most cases, power can be transmitted without any problems in the re-closing power transmission operation in which the switch 5 is automatically closed several seconds to several minutes after a power outage. occupy This is because the ground fault point exhibits gap-like characteristics, and the short-term power outage causes insulation recovery of the discharged gap.

However, with conventional ground fault protection, due to a reclosing fault that is not a permanent ground fault,
This often resulted in short-term power outages lasting from several seconds to several minutes, and because these power outages could not be predicted in advance, they often caused great damage to customers. In addition, once a successful reclosing accident occurs, it means that there is some kind of defect in the track, and since such successful reclosing accidents occur frequently after that, and it is extremely difficult to locate the accident point, it is a social issue. This sometimes became a big problem.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above.In the event of a ground fault accident, the ground fault phase is detected and the ground fault phase is grounded for a short time using a grounding switch. The purpose is to provide a device that can prevent power outages. An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows an embodiment in which a short-time power outage prevention device 9 according to the present invention is installed on a three-phase distribution line 2 in the system shown in FIG. 10 is several meters when a ground fault occurs
11a, 11b, 11c are switches connected in a star shape to each of the three phases to ground only the grounded fault phase at high speed; 12 are switches 11a, 11b, 11c based on the signal from the ground fault phase detection device 10.
The cable 13 that sends the signal to operate the switch is a non-linear resistor, such as a zinc oxide element, which has voltage-current characteristics as shown in FIG. 4, and is connected between the neutral point of the switch 11 and ground. Ru. Reference numeral 14 denotes a ground release switch connected in parallel to this, which opens approximately 10 cycles at commercial frequency after operation of either switch 11b or 11c. Here, switches 11a, 11b, 11c and 14 are reset at an appropriate time after operation.

Next, the operation will be explained. In Figure 3,
If there is no ground fault at the ground fault point 7, the ground fault phase detection device 10 will not operate and the switches 11a, 11b,
11c remains open, so the situation is exactly the same as in the case without the short-term power outage prevention device 9 according to the present invention.
Power is transmitted without affecting the lines.

On the other hand, in this state, gap-shaped ground fault point 7
The temporal operating conditions when a successful reclosing ground fault occurs will be explained with reference to FIG.

In FIG. 5, v _a is the a-phase ground voltage waveform where the ground fault point is thought to be, and it is assumed that the ground fault occurs at time t ₀ when the voltage waveform suddenly decreases as shown in the figure. When a ground fault occurs, a zero-sequence voltage v ₀ occurs as shown in the vector diagram in Figure 2,
The three-phase balance of the ground voltage is disrupted. The ground fault phase detection device 10 vector-synthesizes these voltages and identifies the ground fault phase in a short period of several milliseconds, but as shown in the example in Fig. 2, the ground fault resistance value R _g is small. In the case of a fault under this condition, the voltage to ground v _a of the fault phase is significantly smaller than the others, so the ground fault phase can be determined without relying on vector synthesis means. After determining the ground fault phase,
The switch 11a for the fault phase of the grounding switch is closed at time _t1 to ground the fault phase. When the faulty phase is grounded, the ground voltage v _a of the a phase becomes completely zero.

In the above method, once the fault phase is grounded, the ground fault current flowing through the gap-shaped ground fault point 7 disappears, and the energy injected into the ground fault point 7 disappears, so that it remains in a conductive state. Gap insulation recovery begins. This is shown in FIG. In FIG. 6, the horizontal axis shows time, the vertical axis shows insulation recovery voltage, and the shaded area between the solid lines shows variations. Further, the origin corresponds to the point at which the current is interrupted at the gap-shaped ground fault point 7, and the broken line B indicates the discharge voltage immediately before the ground fault fault. Although it depends on the characteristics of the fault point, as shown in Figure 6, if the no-voltage state continues for approximately 100ms, the insulation at the successful reclosing fault point will recover, and in some cases the voltage will be higher than the discharge starting voltage B. There is. Therefore, by grounding the faulty phase for a short time, it is possible to restore the line to its original normal state.

Next, at time _t2 in FIG. 5, the switch 14 is opened. When the switch 14 is opened, the non-linear resistor 13 is automatically connected to the fault phase. The characteristics of this nonlinear resistor 13 are shown in FIG. 4, and depending on the line-to-ground capacity 6, for a current I _r of about 10 μA to 100 A, the limiting voltage V _r is about the peak value E of the three-phase power supply voltage. choose. If you select like this, switch 1
4 can be prevented from occurring after the circuit is opened, a voltage higher than the peak value E of the line voltage will not be applied, and re-discharge at the fault point caused by the abnormal voltage can be prevented.

This point is a unique effect of this invention, so
I will explain in more detail.

Here, if we consider the case where there is no nonlinear resistor 13, the current flowing through the switch 14 is a current that has advanced by approximately π/2 [rad], as can be understood from the zero-sequence current, and when the switch 14 is opened, , the peak voltage V ₀ of the zero-sequence voltage V ₀ described above remains on the line as a DC voltage component. Therefore, after time _t2 , the ground voltage becomes a DC voltage in which the original AC component becomes a pulsating component, and at its maximum, an abnormal voltage that is exactly twice as high as the original normal voltage is applied. It has been known that this phenomenon causes intermittent arcing ground faults caused in three-phase ungrounded distribution lines. This relationship is the fifth
In the figure, it is v′ _a shown by a dashed-dotted line.

However, as in this invention, the switch 1
4 is opened and the non-linear resistor 13 is connected to the fault phase. As shown by the solid line after time _t2 in FIG. 5, the operation of the non-linear resistor 13 causes the abnormal voltage to become Due to the relationship, the voltage to ground is suppressed to the original peak value E. Therefore, it is possible to prevent the fault point from being redischarged and grounded due to the abnormal voltage generated when the switch 14 is opened.

In this case, if the switches 11a, 11b, 11c, and 14 are returned to the reset state at time _t3 before the substation relay operates, the nonlinear resistor 1
The current flowing through 3 can prevent the substation relay from operating. Moreover, in this case, the switch 11a,
Of course, the circuits 11b and 11c become open first.

In the above explanation, the gap-shaped ground fault point 7 of one phase was described, but although the probability of occurrence of such an accident is low, the gap-shaped ground fault points 7 are 7a and 7b as shown in Fig. 7. There are two locations, and a ground fault may occur with a slight time difference. In this case, by inserting an impedance element Z such as a resistor, capacitance, inductance, or non-linear resistance in series with the switch 11, the short-circuit current flowing through the line can be limited to a small value in the event of a two-point ground fault. . In this case as well, the short-term power outage prevention function of the short-term power outage prevention device 9 in the event of a ground fault at one location remains unchanged.

As described above, according to the present invention, in an ungrounded three-phase three-wire power distribution line, by grounding the ground fault phase for a short time in the event of a ground fault, it is possible to recover the insulation caused by a gap-shaped ground fault, and at the same time By using a circuit that connects a non-linear resistor to the faulty phase during the short-term grounding, we have prevented the occurrence of abnormal voltage in the distribution line after the grounding has been released, thereby preventing a short-term power outage caused by a successful re-closing accident. can be definitely eliminated. Additionally, this has the advantage that damage to customers due to power outages can be kept to a minimum, only in the event of a permanent accident.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a conventional ground fault protection method for power distribution lines, Fig. 2 is a diagram showing voltage vectors at the time of a ground fault, and Fig. 3 is an embodiment of a short-term power outage prevention device according to the present invention. A diagram showing the configuration when applied to a power system, FIG. 4 is a diagram showing the voltage-current characteristics of a nonlinear resistor, and FIG. 5 is a diagram showing the operating time of the short-time power outage prevention device shown in FIG. 3. Figure 6 is a diagram showing the insulation recovery characteristics of a gap-shaped ground fault with successful reclosing.
The figure is a connection diagram showing another embodiment of the short-time power outage prevention device of the present invention. In the diagram, 1 is a three-phase AC power supply, 2 is a three-phase distribution line, and 3
is an instrument transformer, 4 is a ground fault relay, 5 is a switch,
6 is the ground capacitance, 7 is the ground fault point, 9 is the short-term power outage prevention device, 10 is the ground fault phase detection device, 11,1
4 is a switch, 12 is a cable, 13 is a nonlinear resistor, and Z is an impedance element. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A ground fault phase detection device for detecting a ground fault phase of an ungrounded three-phase three-wire power distribution line, a grounding switch connected to each of the three phases in a star shape, and the star-shaped connection. It consists of a non-linear resistor connected between the neutral point and the ground, and a grounding release switch connected in parallel to this non-linear resistor. The faulty phase is grounded by the grounding switch, and after a predetermined time, the grounding release switch is opened to connect the non-linear resistor to the faulty phase, and before the substation ground fault relay operates, the grounding switch is grounded. A short-time power outage prevention device characterized by having a configuration that resets a switch and a ground release switch. 2. The short-time power outage prevention device according to claim 1, wherein each phase of the grounding switch is provided with an impedance element connected in series. 3. The voltage-current characteristic of the non-linear resistor is set to a current range of 10 μA to 100 A when the voltage is at the peak value of the three-to-earth voltage. Short-term power outage prevention device.