JPH0140591B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reactive power supply device that is connected to a power transmission and distribution system (hereinafter referred to as the power system) and supplies reactive power, and in particular aims to improve the stability of its operation. It is something to do.

FIG. 1 is a one-line diagram showing an example of a conventional reactive power supply device. In the figure, 1 is a transmission and distribution line of the power system, 2 is a means for supplying phase-advancing reactive power, that is, a means for consuming lagging-phase reactive power, and this means 2 includes a reactor 21 and a thyristor 22 connected in antiparallel to each other. It is composed of a series body consisting of. 3 is a capacitor that supplies slow-phase reactive power, that is, consumes advanced-phase reactive power; 4 is a control device that controls the firing of the thyristor 22; and 40 is a DC voltage that corresponds to the amplitude value of the voltage from the AC voltage of the power transmission and distribution line. The conversion circuit 45 for converting into a signal is an ignition signal generation circuit. 5 is a signal line that transmits a voltage signal of the power system.

Next, the operation will be explained. The control device 4 applies an ignition signal to the thyristor 22 in synchronization with the voltage waveform of the power system.

FIG. 2 shows the waveform of the voltage V of the power system (that is, the voltage waveform applied across the series body of the reactor 21 and the thyristor 22) and the waveform of the current i _L flowing through the reactor 21. When the timing of the ignition signal is changed, the time τ during which the current is flowing changes, and the waveform of the current also changes, so it is possible to change the amount of lagging reactive power consumed from the power system.
On the other hand, since the capacitor 3 supplies lagging reactive power, the difference in lagging reactive power is supplied to or consumed by the grid.

When the conduction angle of the thyristor 22 is widened to increase the amount of slow phase reactive power consumed, the voltage value of the power system decreases, and when the conduction angle is decreased, the voltage value increases.
Using this effect, the AC voltage of the power system is input to the conversion circuit 40 via the signal line 5, and a DC signal corresponding to the voltage amplitude value is output. This signal is input to the ignition signal generation circuit 45, and the ignition signal is controlled according to the magnitude of the DC signal, thereby maintaining the voltage of the power transmission and distribution line at a constant reference value.

Conventional reactive power supply equipment that operates in this manner has the disadvantage that if an accident such as a short circuit or ground fault occurs in the power system, the voltage of the power system will drop significantly during the accident. attempts to maintain the voltage of the power grid at a constant value by supplying a large amount of slow-phase reactive power to the grid.

When the fault is removed and the grid recovers in this state, the voltage of the power grid increases and the lagging reactive power is no longer needed. However, since the reactive power supply device cannot respond instantaneously, the transient period until the control device 4 confirms that the voltage has increased and reduces the delayed phase reactive power supplied to the power grid is delayed. This results in a state in which reactive power continues to be supplied, and as a result, the voltage of the power system increases abnormally compared to a case where there is no reactive power supply device.

In addition, when the power system is multi-phase, for example, when there are three phases, if an unbalanced accident such as a single-line ground fault occurs,
As shown in Fig. 3 (in Fig. 3, the voltage when the C phase is grounded is shown as a vector), the average voltage decreases, so in order to maintain the voltage, the control device 4 Generates an ignition signal to raise the
Therefore, there was a problem in that the voltage of the healthy phase increased at the same time as the failed phase.

The present invention was made in order to eliminate the drawbacks of the conventional device as described above. In normal times, like the conventional device, the voltage signal at a predetermined position in the power system (hereinafter referred to as system voltage) is used as an input signal to the control device. In contrast, when a grid fault occurs, the input signal to the control device is fixed at the value of the grid voltage immediately before the fault without using the grid voltage, and during the fault, that value is maintained and After removal, by configuring the equipment to use the grid voltage again, abnormal responses of the reactive power supply equipment during an accident can be prevented, and the system will be stable during and after the accident and will not have a negative impact on the power system. The purpose is to provide equipment.

An embodiment of the present invention will be described below.
FIG. 4 is a circuit diagram showing an example of a reactive power supply device according to the present invention. In Fig. 4, 1 is a power system, 2 is means for supplying phase-advanced reactive power, and 2
1, 23, 25 are reactors, 22, 24, 26
are thyristors connected in antiparallel, thyristors 22a, 22b, 24a, 24b, 26, respectively.
It consists of a and 26b. 3 is a capacitor that supplies delayed phase reactive power. 4 is thyristor 22
a, 22b, 24a, 24b, 26a, and 26b; 41 is a diode bridge rectifier that rectifies the AC voltage of the system and converts it into a DC signal corresponding to the voltage amplitude value; 42; 43 is a resistor, and 43 is a capacitor, which constitutes a smoothing filter for removing ripples contained in the signal rectified by the rectifier 41. 44 is a sample hold circuit, 45 is an ignition signal generation circuit, 46
is a signal changeover switch, and 47 is an accident signal line. 5 is a signal line that transmits a system voltage signal, and includes a diode bridge rectifier 41 and an ignition signal generation circuit 45.
is supplying signals to. This embodiment is an example of a three-phase circuit commonly used in power systems.

The operation of the device configured in this way will be explained below. First, under normal conditions, the switch 46 is set to the opposite position from that shown in FIG.
A DC system voltage signal smoothed by a resistor 42 and a capacitor 43 is directly input to an ignition signal generating circuit 45. The ignition signal generating circuit 45 changes the timing of the ignition signal in accordance with this voltage signal to perform control to keep the system voltage constant as in the conventional example. This timing is determined by using the system voltage signal input via the signal line 5 as a reference signal for synchronization.

Next, a case where an accident occurs in the power system will be explained. When an accident occurs, the accident signal line 47 becomes an accident indication voltage. As a result, the sample-and-hold circuit 44 enters Holtz mode, and its output maintains the value immediately before the accident. At the same time,
Since the signal changeover switch 46 is set to the position shown in FIG. 4, a voltage signal equal to that before the accident is input to the ignition signal generation circuit 45 by the sample hold circuit 44. The reactive power supply maintains the same operating state as before the accident. After that, when the fault is removed, the fault signal line 47 returns to the normal voltage and the changeover switch is set to the opposite state as shown in FIG. 4, so the resistor 4
2. The system voltage signal smoothed by the capacitor 43 is directly input to the ignition signal generation circuit 45 to restore normal operation.

In order to explain the characteristics of such an operation in more detail, changes in the grid voltage and reactive power supplied by the reactive power supply device (denoting slow phase reactive power as positive) at the time of an accident will be illustrated and explained.

FIG. 5 shows changes in system voltage (amplitude value) Vs, ignition signal generation circuit input voltage Vc, and reactive power Qs supplied by the reactive power supply device during an accident when a conventional reactive power supply device is used. In the figure, before the accident, the system voltage Vs was maintained at the set value, but when an accident occurs at time F, the voltage of Vs decreases, and the voltage of Vc also decreases. As a result, the ignition signal generation circuit 45 operates to change the operating point of the reactive power supply device and increase the amount of delayed phase reactive power supplied to the transmission and distribution lines so that the system voltage Vs returns to the set value. The grid voltage Vs rises again.

However, if the accident ends in this state, the reactive power required to maintain the grid voltage Vs at the set value may be almost the same as before the accident, but the reactive power supply equipment will be delayed by the same amount as during the accident. Since phase reactive power is being supplied, the power system will have an excess of delayed phase reactive power, and the system voltage Vs will rise significantly above the set value, which may damage other equipment connected to the power system. It was hot.

In contrast, according to the present invention, as shown in FIG. 6, the voltage of the power system can be maintained without generating abnormally high voltage. In the figure, when the accident starts at time F, the system voltage Vs decreases, but at the fourth
Since the sample and hold circuit 44 shown in the figure operates, the ignition signal generation circuit input voltage Vc is maintained at the state before the accident. Therefore, the reactive power supplied by the reactive power supply device is equal to that before the accident. During the accident, the system voltage Vs remained low, but there is no risk of destroying other equipment and there is no problem. Furthermore, even in the event of an unbalanced accident, the voltage of the healthy phase will not rise abnormally.

When the accident ends, the reactive power required to maintain the grid voltage Vs at the set value can be almost the same as before the accident, so the difference between the reactive power and the reactive power supplied by the reactive power supply device is small. , the grid voltage Vs will not jump. From this state, the input voltage of the ignition signal generation circuit is switched again from the output of the sample-and-hold circuit 44 to the grid voltage smoothed by the filter, so that the voltage of the power grid returns to the reference value without large fluctuations.

As described above, according to the present invention, a changeover switch is provided that switches to the output side of the voltage derivation circuit when the power system is healthy, and to the output side of the holding circuit when a failure occurs in the power system. Since the firing angle of the control switching device is controlled according to the value of the output of the voltage derivation circuit or the value of the output from the holding circuit given through the switching circuit, short-circuit accidents, ground faults, etc. When an accident occurs, the changeover switch switches from the output side of the voltage derivation circuit to the output side of the holding circuit, and the value output from the voltage derivation circuit immediately before the accident occurs is transferred to the ignition signal generation circuit via the holding circuit. It will be output to . Therefore, even if the power grid voltage drops, the changeover switch will change, so the voltage signal given to the ignition signal generation circuit will be maintained at the voltage signal it had just before the accident, and a situation where a capacitor with an equivalently large capacity would continue to be applied may occur. Therefore, there is no jump in the power system voltage at the time of recovery from an accident. Furthermore, since there is no problem even if there is a slight delay in signal detection, the present invention can be sufficiently applied to cases where a protective relay is used to examine an accident in detail before outputting an accident signal. In addition, 1 shown here
Needless to say, the same effect can be obtained not only in the case of a line-to-ground fault but also in other accidents by using a circuit that can maintain the voltage of the signal before the accident. In place of the two thyristors connected in anti-parallel in the above embodiment, a bidirectional thyristor may be used, or two transistors connected in anti-parallel may be used. In short, any control switching device that can control the current flow angle in both directions may be used.

[Brief explanation of drawings]

Figure 1 is a configuration diagram showing an example of a conventional reactive power supply device, and Figure 2 is a voltage waveform V applied to a series body of a reactor and an anti-parallel thyristor of the reactive power supply device and a current waveform i _L flowing through the reactor. Figure 3 shows the waveform diagram at the time of an unbalanced accident (C phase 1 wire ground fault)
4 is a diagram showing the configuration of an embodiment of the reactive power supply device according to the present invention, and FIG. 5 is a vector diagram showing the system voltage of the conventional reactive power supply device in the event of an accident. FIG. 6 is a waveform diagram of each part corresponding to FIG. 5 when the reactive power supply device according to the present invention is used. In the figure, 1 is a power system transmission and distribution line, 2 is a phase-advanced reactive power supply means, 21 is a reactor, 22 is an anti-parallel thyristor, 3 is a capacitor, 4 is a control device, 40 is a voltage signal AC/DC converter, 45 is an ignition signal generation circuit, 5 is a voltage signal line, 22a, 22
b, 24a, 24b, 26a, 26b are thyristors, 24, 26 are anti-parallel thyristors, 23, 25
4 is a reactor, 41 is a diode bridge rectifier, 42 is a resistor, 43 is a capacitor, 44 is a sample hold circuit, 45 is an ignition signal generation circuit, 4
6 is a signal changeover switch, and 47 is an accident signal line. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A reactor that supplies reactive power to an electric power system, a control switching device that controls the flow angle of current flowing through the reactor, and a voltage derivation that generates an output according to the magnitude of the voltage of the electric power system. The output from the circuit and the voltage derivation circuit is taken in and held, and the held output is updated at predetermined intervals, and when an accident occurs in the power system, the updating operation is stopped and the accident occurs. a holding circuit that maintains the held value immediately before the occurrence of the voltage derivation circuit; a first signal transmission system that uses the output of the voltage derivation circuit as a signal for controlling the flow angle; and a first signal transmission system that uses the output of the holding circuit as a signal for controlling the flow angle. a second signal transmission system to be used, and a changeover switch that selects the first signal transmission system when the power system is healthy and selects the second signal transmission system when an accident occurs in the power system. and a firing signal generation circuit that controls the firing angle of the control switching device based on the signal from the signal transmission system selected by the changeover switch. 2. The reactive power supply device according to claim 1, wherein the holding circuit includes a sample and hold circuit. 3. The reactive power supply device according to claim 1, wherein the control switching device includes thyristors connected in antiparallel to each other. 4. The reactive power supply device according to claim 1, wherein the reactor and the control switching device are connected between a power system and a neutral point or the ground.