JPS58255B2 - capacitor switchgear - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capacitor switching device using semiconductor switching elements.

FIG. 1 shows a conventional capacitor switchgear, in which 1 is connected to a three-phase power system 2 via a switch 3.
In the phase transformer, the primary winding 4 is connected in a delta configuration, and the secondary winding 5 is connected in a star configuration.

A capacitor 6 is connected to the U phase of the secondary winding 5 of the three-phase transformer 1.
A thyristor switch circuit 9 composed of an antiparallel circuit of a diode 7 and a thyristor 8 is connected in series.

Similarly, a capacitor 10 and a thyristor switch circuit 13 composed of an anti-parallel circuit of a diode 11 and a thyristor 12 are connected in series to the V phase of the secondary winding 5 of the three-phase transformer 11. A capacitor 14 and a thyristor switch circuit 17 constituted by an anti-parallel circuit of a diode 15 and a thyristor 16 are connected in series to the W phase of the secondary winding 5 .

Thyristor switch circuit 9, 13.17 capacitor 6
．． The terminals opposite 10° 14 are connected in common, and this common connection point 18 is connected to the neutral point 19 of the secondary winding 5 of the transformer 1.

When turning on the capacitors 6.10.14, first close the switch 3 to start the device, and then turn on the capacitors 6.1 for each phase.
Cyrisk switch circuit 9,13 connected to 0.14
．． Thyristor 8,
12.16 is ignited to prevent inrush current when the capacitor is turned on.

However, in this type of conventional capacitor switchgear, when the switch 3 is closed at startup, the charge on the capacitor 6, 10, 14 is zero before startup, so
Thyristor switch circuit 9゜13.17 thyristor 8
, 12, 16 are non-conductive, a large inrush current may be generated in each thyristor switch 9 depending on the closing phase of the switch 3.
, 13°17 through the diode 7.11.15.

For this reason, a diode 7.11 may be used in some cases.

However, there are disadvantages in that the diodes 7, 11, 15 and capacitors 6, 10, 14 may be destroyed or their lifespans may be shortened.

In addition, conventional capacitor switching devices do not have a function to limit the short-circuit current when a capacitor malfunctions and short-circuits, so this short-circuit current can damage the case of the short-circuited capacitor or destroy the thyristor and diode. There was a risk that this would occur.

Therefore, among these problems, a device as shown in FIG. 2 has been proposed as a solution to the problem of rush current at startup.

That is, in the capacitor switching device shown in FIG. 2, the switch 20 is opened at the time of startup, and the inrush current flowing through the switch 3 is limited by the current limiting resistor 21, so that a steady state is reached. At this point, the switch 20 is closed and the current limiting resistor 21 is short-circuited.

However, in such a capacitor switching device, two switches are required for each phase, which poses an economical problem.

Further, there were other drawbacks such as no solution to overcurrent caused by short circuit of the capacitor.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a capacitor switching device that has an extremely simple configuration and eliminates all the drawbacks of the conventional devices as described above.

An embodiment of the present invention shown in FIG. 3 will be described in detail below.

In FIG. 3, numerals 1 to 19 are the same as those of the conventional capacitor switching device shown in FIG. 1, so explanations thereof will be omitted.

22 is a current limiting resistor connected between the common connection point 18 and the neutral point 19 of the secondary winding 5 of the transformer 1.

This invention is configured as described above, and when the switch 3 is closed at the time of startup, at this point, the thyristor switch circuit 9,
Since each thyristor 8, 12, 16 of 13.17 is all non-conducting, all inrush current to capacitor 6, 10, 14 is transferred to diode 7, 11, 15 and current limiting resistor 22.
and is current limited by this current limiting resistor 22.

Therefore, the current after being limited by the resistance value of the current limiting resistor 22 flows through the capacitor 6.10.14 and the diode 7.11.
．． By selecting a value that does not cause any problem, the problem of rush current at startup can be solved.

Moreover, this inrush current becomes zero once the charging of each capacitor 6, 10° 14 through the diodes 7, 11, 15 is completed, so the current flows through the current limiting resistor 22 for a very short time. , the current rating of the current limiting resistor 22 may be small.

Thyristor 8, 12.16 is fired and capacitor 6.1
0.14, the thyristor switch circuits 9, 13, 17 of each phase are
When the voltage across the thyristors 8, 12, .
16 is fired.

That is, the three-phase capacitors 6, 10, and 14 are not turned on at the same time, but are turned on sequentially for each phase with a 120° shift.

Therefore, it takes 2 hours until all three phase capacitors are turned on.
During the /3 cycle period, the currents in each phase are not balanced, and current flows through the current limiting resistor 22.

However, this period is very short. When all three-phase capacitors 6, 10, and 14 are connected, current flows between the neutral points 18 and 19, that is, the current limiting resistor 22, because the currents of each phase cancel each other out and become zero. do not have.

Therefore, the current rating for this period is not required.

Next, the operation when the capacitor is shorted will be explained.

For example, if the u-phase capacitor 6 is short-circuited, the short-circuit current will be: u-phase secondary winding 5 - shorted capacitor 6 - thyristor switch circuit 9 - neutral point 18 - current limiting resistor 22 - neutral point 19 -Because it flows through the closed circuit of the secondary winding 5,
This short-circuit current is limited by the current-limiting resistor 22, and destruction of the capacitor 6 and the thyrisk switch circuit 9 in the closed circuit through which the short-circuit current flows is prevented.

In the above description, a resistor is used as the current limiting element, but the present invention is not limited to this, and it goes without saying that the same effect can be achieved by using other current limiting elements, such as a reactor.

As described above, the capacitor switching device of the present invention has an extremely simple configuration that protects the capacitor and the semiconductor rectifier circuit connected in series with the capacitor from inrush current at startup and short-circuit current when the capacitor is short-circuited. It has the effect of being able to.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams of a conventional capacitor switching device, and FIG. 3 is a circuit diagram of a capacitor switching device according to an embodiment of the present invention. In the figure, 1 is a three-phase transformer, 3 is a switch, 4 is a primary winding, and 5 is a three-phase transformer.
is the secondary winding, 6, 10.14 is the capacitor, 9, 13.
17 is a thyrisk switch circuit, and 18 and 19 are neutral points. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. The above-mentioned 2. A capacitor switching circuit connected in a star shape to the next winding, and a current-limiting element connected between the neutral point of this star-shaped capacitor switching circuit and the neutral point of the secondary winding of the transformer. A capacitor switchgear comprising: 2. The capacitor switching device according to claim 1, wherein the semiconductor switch circuit is comprised of an anti-parallel circuit of a diode and a silice.