JPH04411B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a protection circuit for a semiconductor switch used in a tap changer of a transformer.

[Conventional technology]

Fig. 1 shows a conventional example of a protection circuit provided in a semiconductor switch of a tap changer.
and generates a circuit voltage Vp. Further, a potential difference of the tap-to-tap voltage Vs occurs between the switching taps 1A and 1B (the circuit voltage Vp is sufficiently higher than the tap-to-tap voltage Vs). 2A and 2B are the switching elements of the tap changer (for switching the voltage between taps Vs)
It is an anti-parallel thyristor switch, which is connected to switching taps 1A and 1B, and the thyristor
SCR1 and SCR2 are connected in antiparallel. 3A,
3B is a voltage suppressing element (surge arrester) with a limiting voltage Va, and each anti-parallel thyristor switch 2
A and 2B are connected in parallel, and the overvoltage applied between the anode and cathode of the anti-parallel thyristor switches 2A and 2B is suppressed to below the limit voltage Va to prevent overvoltage breakdown. Naturally, the limiting voltage
Va needs to be higher than the tap-to-tap voltage Vs,
Anti-parallel thyristor switches 2A and 2B are limited voltage
It is necessary to have a withstand voltage capability higher than Va. (However, until the withstand voltage capability of anti-parallel thyristor switches 2A and 2B is made higher than the circuit voltage Vp,
It is economically and dimensionally disadvantageous. ) 4A and 4B are current interrupting elements (protection fuses) for protecting the anti-parallel thyristor switches 2A and 2B, and are connected in series to the load 5 side of the anti-parallel thyristor switches 2A and 2B, respectively. As described above,
The limit voltage Va is set higher than the tap-to-tap voltage Vs, but on the other hand, the circuit voltage Vp is set higher than the tap-to-tap voltage Vs.
Set as low as possible. The degree to which it can be lowered is determined by the withstand capacity of the voltage limiting element and the required application time of the circuit voltage Vp (in normal conditions, only the tap-to-tap voltage Vs is applied, so there is no problem; (also relates to circuit protection and disconnection in the event of a circuit break).

In this configuration, it is assumed that the anti-parallel thyristor switch 2A is now turned on and the switching tap 1A is selected (fired). That is, the circuit voltage Vp
A current approximately determined by the load 5 is applied. At this time, as a matter of course, the anti-parallel thyristor switch 2B is off. If the anti-parallel thyristor switch 2B is erroneously fired in this state, a short circuit will occur between the switching taps 1A and 1B, and the voltage between the taps Vs
The short-circuit overcurrent (more precisely, the vector sum with the current flowing through the load 5) determined by the switching tap 1A - anti-parallel thyristor switch 2A - current interrupting element 4A - current interrupting element 4B - anti-parallel thyristor switch 2B - The current flows through the switching tap 1B, and the current interrupting elements 4A and 4B are blown out. Thus, the above short circuit current is interrupted, but after this current interruption,
Between the terminals of the fused current interrupting elements 4A and 4B (gap formed after the protective fuse is blown)
In between, a voltage of approximately the same magnitude as the circuit voltage Vp (>Va>Vs) is applied as a recovery voltage (because until then, current had been flowing to the load 5, but the circuit became open due to the interruption, and the aforementioned melted Approximately the circuit voltage across the space gap of the fuse that will be formed later.
This is because Vp occurs).

Therefore, in the conventional protection circuit described above, the dielectric strength between the terminals of the protective fuses 4A and 4B is determined by the circuit voltage Vp.
The insulation distance must be greater than or equal to the circuit voltage.
Vp, the current interrupting element has the disadvantage that its rated voltage is equivalent to the above-mentioned circuit voltage, making it large and expensive.

[Summary of the invention]

This invention was made to eliminate the above-mentioned conventional drawbacks, and by connecting a voltage suppressing element in parallel to a series circuit of a semiconductor switch and a current interrupting element, the voltage of the current interrupting element can be reduced. The purpose of the present invention is to provide a protection circuit for semiconductor switches that can significantly reduce the rating, reduce size, and reduce costs.

[Embodiment of the Invention] FIG. 2 is a circuit diagram showing an embodiment of the present invention, in which a voltage suppressing element 3A is connected in parallel to a series circuit of an anti-parallel thyristor switch 2A and a protection fuse 4A, This differs from the one shown in FIG. 1 in that the voltage suppressing element 3B is connected in parallel to the series circuit of the anti-parallel thyristor switch 2B and the protective fuse 4B.

In this configuration, as described above, if the anti-parallel thyristor switch 2B is erroneously fired while the anti-parallel thyristor switch 2A is firing, a short circuit occurs between the switching taps 1A and 1B, and the voltage between the taps increases.
Short-circuit overcurrent of magnitude determined by Vs (more precisely,
The vector sum of the current flowing through the load 5) flows through the switching tap 1A - anti-parallel thyristor switch 2A - current interrupting element 4A - current interrupting element 4B - anti-parallel thyristor switch 2B - switching tap 1B,
Current interrupting elements 4A and 4B are fused.

When the short-circuit overcurrent is interrupted, a circuit voltage Vp begins to appear between the terminals of the current interrupting elements 4A and 4B, but when the level of this voltage reaches approximately the limiting voltage Va of the voltage suppressing elements 3A and 3B, Since these voltage suppressing elements 3A and 3B operate, the voltage applied between the terminals of the current interrupting element 4A is such that the voltage drop across the anti-parallel thyristor switch 2A is the limiting voltage Va.
Since it is very small compared to , if you ignore it, it will be suppressed to the size of the limit voltage Va. Current interrupting element 4
The same applies to B. Therefore, the rated voltage of the current interrupting elements 4A and 4B (the voltage that must withstand the recovery voltage generated between the terminals immediately after interrupting the circuit) is not the circuit voltage Vp, but clears the limiting voltage Va, which is much lower than this. This is a good thing (as mentioned above, the limit voltage Va is set lower than the circuit voltage Vp).

Overvoltage protection for the anti-parallel thyristor switches 2A, 2B is performed by the voltage suppressing elements 3A, 3B in the same manner as in the past, since the voltage drop across the current interrupting elements 4A, 4B is 0.

Although the above description has been made of the case of a semiconductor switch incorporated in a tap changer, the present invention can be applied to a semiconductor switch that is a component of a power control circuit or a device to obtain similar effects.

Further, the semiconductor switch is not limited to an anti-parallel thyristor switch.

〔Effect of the invention〕

As explained above, this invention has a structure in which a voltage suppressing element is provided in parallel to a series circuit of a semiconductor switch and its current interrupting element, so that the voltage rating of the current interrupting element is set to the limiting voltage of the voltage suppressing element. Since it can be reduced to a level of

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional example of a protection circuit provided in a semiconductor switch of a tap changer, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the figure, 1...Tap switching transformer, 1A,
1B...Switching tap, 2A, 2B...Anti-parallel thyristor switch, 3A, 3B...Voltage suppression element,
4A, 4B...Protection fuses that are current interrupting elements. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A semiconductor switch equipped with a current interrupting element for overcurrent protection of a semiconductor switch inserted between each switching tap of a tap changer and a load, and a voltage suppression element for overvoltage protection of the semiconductor switch. A protection circuit for a semiconductor switch, characterized in that the current interrupting element is connected in series with the semiconductor switch, and the voltage suppressing element is connected in parallel with the series circuit.