JPH0417450B2 - - Google Patents

Description

[Detailed description of the invention]

In a three-phase circuit in which independent single-phase loads are connected between each phase, the present invention detects the line current of each three phases, identifies which phase the load is, and opens and closes reactive power generators such as capacitors for each phase. The present invention relates to a reactive power control device that performs reactive power control. Figure 1 shows a circuit diagram of a conventional reactive power control device, where 11, 12, and 13 are three-phase RSTs.
It is a single-phase load connected between each phase of Conventionally, in general, each load 11, 12, 1
3, a current transformer (hereinafter referred to as CT) 21a,
22a and 23a detect the load current, and thereby operate the semiconductor switches 41, 42, 43 via the control units 31, 32, 33, and open/close the capacitors 51, 52, 53 connected between each phase to disable them. Electric power was controlled. However, in the case of a factory where many loads with relatively small capacity and low power factor, such as welding machines, are distributed over a wide area, it is necessary to connect a CT to each load and wire each one separately. This required a great deal of effort and effort for each operation confirmation test. The present invention is characterized in that when such a large number of single-phase loads are distributed, the current of each phase is detected on the sending side of a three-phase feeder to control a reactive power generating device such as a capacitor. The present invention aims to provide a reactive power control device that does the following. The main structure of the embodiment of the present invention will be explained with reference to FIG. 11, 12, 13 are single-phase loads connected to each phase, 21b, 22b, 23b are line current detection CTs for each phase, and 61, 62, 63 are for instruments for timing pulses of each phase. Transformer (hereinafter
PT), and 31, 32, and 33 are
This is a control device that performs calculations based on the secondary outputs of CT and PT. 51, 52, 53 are capacitors connected between each phase, and these are semiconductor switches 41, 42, 43 controlled by control devices 31, 32, 33.
It is opened and closed by 3 and 4 show the configuration inside the control device, 71R, 71S, 71T are detection circuits for determining the presence or absence of each line current, 80R, 80S, 80
T is an inverter circuit, 90R, 90S, and 90T are AND circuits, 95R, 95S, and 95T are current or reactive power detection circuits, and 96R, 96S, and 96T are switching circuits controlled by the above 90R, 90S, and 90T. . To explain the operating principle using FIG. 3, for example, R
-The current of the S-phase connected load is the R-phase and S-phase CT21b,
22b, the detection circuits 71R and 71S become H signals, and the detection circuit 71T becomes an L signal. At this time, only the signal of the detection circuit 71T is inverted from the H signal by the inverter circuit, and the AND circuit 90
When three signals are input to R, a logical product is established, and the output becomes L. The load is identified as an R-S phase load, and a signal is given to the reactive power generator to control each phase. In addition, for the R-S phase connected load at this time,
Regarding the operation of the other phase, the detection circuits 71R and 71S are H, and the detection circuit 71T is L, but the inverter circuit 80S
As a result, the signal of the detection circuit 71R becomes L, the input of the AND circuit 90S becomes L, H, L, and the output of the AND circuit 90S remains H, identifying that the load is not of this phase. The logic of identification based on each phase current is shown in the table below.

[Table] Next, in FIG. 4, it is assumed that the current or reactive power value is detected by the circuit described above, and the input amount of the reactive power generator can be varied to perform appropriate control. According to the present invention, when a large number of single-phase loads are installed in a distributed manner, the capacitor can be controlled by detecting the connected phase of the load by simply detecting the voltage and current at the feeder outlet. ,
There is no need to provide equipment for measuring individual load currents, which has the advantage of simplifying the equipment and making it easier to rearrange and modify the loads. Although the configuration in which the capacitor is opened and closed is shown in the above embodiment, a method may also be used in which the phase advance capacitor and the shunt reactor are connected in parallel and the shunt reactor is controlled in phase or opened and closed. If two phases of loads are not energized at the same time, the load current can be detected by the phase current, so it is sufficient to use a single phase as the input power supply, but in reality, due to wiring reasons and In order to equalize the usage rate of each phase of power supply equipment (three-phase equipment) by leveling the load, even single-phase loads that are rarely energized at the same time are installed distributed among each phase of a three-phase circuit. ing. When installing this type of reactive power compensator to control reactive power, wiring may be changed to combine single-phase loads into one phase, but changing the wiring is not easy in reality, so three-phase circuits Reactive power is controlled using a reactive power compensator based on this method. As described above, the reactive power control device of the present invention can simplify the measuring equipment, can be manufactured at low cost, and can be easily changed, and is extremely useful industrially.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional reactive power control device, and FIGS. 2, 3, and 4 are circuit diagrams of an embodiment of the reactive power control device of the present invention. 11, 12, 13: Single phase load, 21b, 22
b, 23b: Current transformer for detecting line current, 3
1, 32, 33: control unit, 41, 42, 43: semiconductor switch, 51, 52, 53: capacitor,
61, 62, 63: Instrument transformer, 71R, 71
S, 71T: detection circuit, 80R, 80S, 80
T: Inverter circuit, 90R, 90S, 90T:
AND circuit, 95R, 95S, 95T: Current or reactive power detection circuit, 96R, 96S, 96T:
switching circuit.

Claims (1)

[Scope of Claims] 1. In a three-phase circuit in which a single-phase load with low usage rate and negligible simultaneous operation is connected between each phase, a detection circuit for each line current and only one phase of its output is passed through an inverter circuit. After that, the connected phase of the single-phase load that is being operated is identified by an AND circuit that ANDs the three signals with the output of the other two phases, and the reactive power generator connected between each phase is connected between each phase. A reactive power control device characterized by controlling each phase in synchronization with the operation of a connected single-phase load. 2. The invalidity according to claim 1, characterized in that a three-phase circuit is provided with a detection circuit for a current value or a reactive power value, and the input amount of a reactive power generator connected to each phase is variably controlled for each phase. Power control device.