JPH02265320A - Overvoltage protection circuit for series thyristor - Google Patents

Abstract

PURPOSE:To continue the operation of series thyristors even when a snubber resistor is overheated by providing a means opening a self-trigger circuit connecting to each thyristor to each of the thyristors when a temperature of the resistor of the snubber circuit reaches a high temperature over a prescribed value. CONSTITUTION:Temperature fuses 19, 29, 99 blown when the temperature of snubber resistors 13, 23, 93 reach a prescribed value or over are fitted to a proper position to detect the temperature of the snubber resistors. When the temperature of the snubber resistor 23 rises through the repetition of triggering a thyristor 20 due to a faulty gate circuit 21 and the gate circuit 21 is not restored, the temperature fuse 29 is blown finally. As a result, the self-trigger circuit for the thyristor 20 is opened to lose the self-trigger function. Then the thyristor 20 is destroyed and short-circuited due to the overvoltage. Since some of series thyristors are provided in general as redundant components, the operation is continued as it is without any hindrance.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention connects a plurality of thyristors in series to a high voltage circuit, and turns on and off each of these thyristors simultaneously to perform power conversion and circuit opening/closing. Related to overvoltage protection circuits for series thyristors.

[Conventional technology]

FIG. 2 is a circuit diagram showing a conventional example of a series thyristor equipped with an overvoltage protection circuit.

In particularly high-voltage power systems, a large number of thyristors connected in series are used, for example in static passive power regulators. When using series thyristors in high voltage circuits like this, protection against overvoltage is especially important.
A circuit configured as shown in FIG. 2 is often used.

In this FIG. 2, a plurality of thyristors 10.20°9
0 is connected in series to the high voltage circuit, but from the on/off command circuit 2 installed on the low potential side,
The on/off command signal is transmitted to the gate circuit 11.21.91 on the high potential side through an insulated optical fiber, so in response to this on/off command signal, the gate circuit 11.21.91 outputs a gate drive signal, and each thyristor 10, 20, 90 turns on or off in unison.

Here, voltage dividing resistors 12, 22, and 92 are connected between the anode and cathode of each thyristor, respectively, and this is for equalizing the voltage shared by each thyristor connected in series.

Also, snubber resistor 13.23.93 and snubber capacitor 1
4. The snubber circuit configured by series connection with 24.94 is
It is connected between the anode and cathode of each thyristor, and this is to relieve the application of a voltage with a large rate of change to the thyristor when the thyristor is turned off.

Furthermore, a self-ignition circuit consisting of a series resistor 15.25.95, a breakover diode (hereinafter abbreviated as BOD) 16.26°96, and a series diode 17.27.97 is connected to the anode of each thyristor.・This is connected between the gates, but this is because when a large surge voltage enters the high voltage circuit to which the series thyristor is connected due to a lightning strike or circuit breaker operation, the self-ignition circuit operates and the thyristor is activated. This is to prevent damage caused by overvoltage.

FIG. 3 is a graph showing the breakover characteristics of BOD, with the horizontal axis representing voltage and the vertical axis representing current.

As shown in FIG. 3, when a forward voltage is applied to the BOD, its value is the breakover voltage (2). This BOD has the characteristic of causing a breakover when it exceeds this value.

Therefore, when a surge voltage enters the high voltage circuit and a voltage higher than the breakover voltage VIO is applied between the anode and cathode of a thyristor, a gate current flows through the BOD that has broken over to the gate of the thyristor. flows and forcibly fires the thyristor, which prevents the thyristor from being destroyed by overvoltage.

As mentioned above, series thyristors connected to a high voltage circuit are protected from overvoltage by each thyristor being equipped with a voltage dividing resistor, a snubber circuit, and a self-ignition circuit. It is common to increase security by adding more than a predetermined number to provide redundancy.

[Problem to be solved by the invention]

As mentioned above, by providing a self-ignition circuit for each series thyristor, it is possible to protect against the intrusion of surge voltage. Furthermore, it operates even in the case of an internal failure of the series thyristors, and provides reliable protection even when overvoltage is applied to each thyristor.

However, if a specific gate circuit, for example, the gate circuit 21, fails and does not allow on-gate t2it to flow through the thyristor 20, the following problem occurs.

That is, when all the series thyristors are turned on at the same time, only the thyristor 20 is off, so the voltage between the anode and cathode of this thyristor 20 rises,
When its value reaches the breakover voltage VIO, BOD
26 breaks over and fires the thyristor 20, eliminating the overvoltage.

At this time, the snubber capacitor 24 has a breakover voltage V
,. When the thyristor 20 turns on, this charged charge becomes heat and is consumed by the snubber resistor 23. Assuming that the capacitance of the snubber capacitor 20 is C, this stored energy W is expressed by equation (1).

w-′/2c-vyo. −・−・−・・・ （
1) This energy W becomes a loss generated in the snubber resistor 23, but when the series thyristor is repeatedly turned on and off, the loss in equation (1) will occur in the snubber resistor 23 each time. , which is several times the loss generated during normal ignition operation.

Increasing the capacitance of the snubber resistor 13.23.93 to withstand this large loss would make the device larger and more expensive, so -S is a resistor with a capacity that can tolerate the loss that occurs during normal operation. I have to.

Therefore, if the above-mentioned abnormality occurs due to a failure in the gate circuit, the high voltage circuit should be cut off or the equipment should be stopped to repair the faulty part to prevent the snubber resistor from burning out. It is undesirable for such a partial failure to cause a power outage in a circuit that requires high reliability or to stop the equipment.

Therefore, an object of the present invention is to enable the series thyristor to continue operating even if the snubber resistor overheats.

[Means to solve the problem]

In order to achieve the above object, the overvoltage protection circuit of the present invention connects a snubber circuit including a resistor and a capacitor between the anode and cathode of a thyristor, and when the voltage exceeds a predetermined value, a current is generated. In a series thyristor in which a plurality of thyristors are connected in series, a self-ignition circuit for overvoltage protection is connected between the anode and the gate, and the resistance temperature of the snubber circuit is at a high temperature exceeding a predetermined value. Each of the thyristors is separately provided with means for opening the self-ignition circuit connected to the thyristor to which the high-temperature resistance belongs when

Note that circuits in which current flows when the voltage exceeds a predetermined value include, for example, a breakover diode, a Zener diode, a diac, or a thyristor/Zener diode combination in which a Zener diode is connected between the anode and gate of the thyristor. circuit can be used.

[Effect]

In this invention, if it is detected that the snubber resistor has overheated,
By disabling the circuit that self-ignites the thyristor to which the high-temperature snubber resistor belongs, the thyristor is short-circuited and destroyed due to overvoltage. In other words, this is equivalent to short-circuiting one of the many thyristors connected in series, and the remaining thyristors are used to continue operation.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In this Figure 1, multiple thyristors! 0.20°9
0 are connected in series to a high voltage circuit, and each thyristor has a gate circuit 11.21 that flows a gate current based on the command from the on/off command circuit 2.
．． 91, and between the anode and cathode of each thyristor are voltage dividing resistors 12.22, 92, snubber resistors 13.23.93, and snubber capacitors 14.92.
The connection of the snubber circuit consisting of 24.94 and 24.94 is the same as in the conventional circuit already described in FIG. Also, the self-starting circuit made up of a series connection of a series resistor 15.25.95, a BOD 16.26.96, and a series diode 17.27.97 is connected between the anode and gate of each thyristor. This circuit is the same as the conventional circuit shown in FIG.

In the present invention, the temperature fuse 19 is fused when the temperature of the snubber resistor 13, 23, 93 exceeds a predetermined value.
．． 29.99 is installed in the optimal position to detect the temperature of each snubber resistor, and this temperature fuse is inserted in series with the self-firing circuit for the thyristor to which each snubber circuit belongs. ing.

With such a circuit configuration, even if the temperature of the snubber resistor 23 rises due to repeated firing of the thyristor 20 due to breakover of the BOD 26 due to a failure of the gate circuit 21, for example, the gate circuit 21 will not be damaged. If it does not recover, the temperature fuse 29 will finally blow. As a result, the self-starting circuit for the thyristor 20 opens and loses its self-starting function. Therefore, the thyristor 20 is destroyed by the overvoltage, resulting in a short circuit. In other words, it is the same as shorting the anode and cathode of one of the many series thyristors, but since some of the series thyristors are generally redundant elements, they can continue to operate without any problems. I can do it.

Although the example circuit shown in Figure 1 uses a temperature fuse, a circuit that uses a bimetal or temperature relay to detect the temperature rise of the snubber resistor and inserts its contact in series with the self-ignition circuit is also possible. Of course, it is also possible to have a configuration. Furthermore, instead of the BOD 16°26, 96, a Zener diode, a diac, or a thyristor in which a Zener diode is connected between the anode and the gate may be used.

〔Effect of the invention〕

According to this invention, when a plurality of thyristors equipped with a snubber circuit and a self-ignition circuit are connected in series to a high voltage circuit, there is a risk that the snubber resistor will burn out due to a failure in the gate circuit, etc. Then, the self-ignition circuit is opened and the thyristor is short-circuited and destroyed due to overvoltage, thereby preventing the device from stopping due to the snubber resistor burning out. Generally, a series thyristor has several redundant elements, so short-circuit damage within the number of redundant elements is within the permissible range, and this has the effect of preventing major damage from occurring due to power outages or stoppages of important equipment. .

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing a conventional example of a series thyristor equipped with an overvoltage protection circuit, and Fig. 3 is a circuit diagram showing a conventional example of a series thyristor equipped with an overvoltage protection circuit. This is a graph that has been updated. 2...On/off command circuit, 10.20.90...
Thyristor, 11.21.91...gate circuit, 12
．． 22.92...Voltage dividing resistor, 13.23.93...
Snubber resistor, 14.24.94... Snubber capacitor, 15.25.95... Series resistance, 1626, 96.
...B OD, 17.27.97...Series diode, figure A

Claims (1)

[Claims] 1) Connect a snubber circuit including a resistor and a capacitor between the anode and cathode of the thyristor, and
In a series thyristor in which a plurality of thyristors are connected in series, a self-ignition circuit for overvoltage protection including a circuit through which current flows when the voltage exceeds a predetermined value is connected between the anode and the gate, and the resistance of the snubber circuit is Each of the thyristors is separately provided with means for opening the self-ignition circuit connected to the thyristor to which the high temperature resistance belongs when the temperature reaches a predetermined value or higher. Features a series thyristor overvoltage protection circuit.