SU775814A1 - Device for protection of ac power supply source - Google Patents

Description

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This invention relates to the field of power supply protection.

A protection and switching device is known that contains an executive unit made on two counter-5 series-connected thyristors shunted by counter diodes, and the cathodes of the thyristors are combined. The disadvantage of it is low reliability when protecting sources. ten

The closest in technical means and the achieved result is a device for protection of an alternating current power source, j containing a current sensor, made in the form of a shunt, in parallel to which through the first resistor are connected the counter-parallel connected LEDs of the first optocoupler, the photodistor 20 of which the resistor is connected to the DC source and the protection executive. A disadvantage of this device is low reliability. 25

In order to increase the reliability, the protection device is equipped with a transformer, the primary winding of which is connected to the alternating current source, and the secondary winding through the phototrisis

the tori of the second optocoupler is connected between the control electrodes of the thyristors

Figure 1 shows the protection device; in fig. 2 shows an embodiment with a transformer without removing the middle point of the secondary winding.

The source contains a series-connected load 1, an overload sensor 2 and two oppositely connected thyristors 3,4. In parallel, the thyristors and counter-diodes 5,6 included, with the anodes of the diodes 5,6 and the cathodes of thyristors 3,4 interconnected. An optocoupler 7 is connected through a resistor to the thyristor control electrode circuits with photo thyristors 8.9.

Claims (1)

If the secondary winding of the transformer 10 is made with a midpoint, the phototransistors 8, 9 of the optocoupler 7 are connected in series with the half windings, and the middle point is connected to the cathodes of the thyristors (figure 1). If the winding is made without an average output, the photothyristors 8.9 of the optocoupler 7 are connected in series with the winding and counter-parallel to each other, and the thyristor control junctions are shunted by the on-opposite diodes (Fig. 2). The primary winding of the transformer 10 is connected to an alternating voltage source. The LED 11 of the optocoupler 7 is connected via limiting resistors 12, 13 to a constant voltage source. Optocoupler 14 shunts resistor 12 and diode 11 of optocoupler 7 with its optical diode 15, LEDs 16 g 17 of optocoupler 14 are connected anti-parallel and through a limiting resistor are connected in parallel with an overload sensor 2 In normal operation. In the absence of overloads and short circuits in the load, the voltage removed from sensor 2 in each half period is not enough to turn on the LEDs 16, 17 of the optocoupler 14. The photo thyristor of this optocoupler is not turned on. When the voltage Uy is turned on, the LED 11 of the optocoupler 7 and the thyristors 8.9 turn on, which perform the function tion diodes in a half-wave rectification circuit. Depending on the sign of the input voltage, it supplies control to one of the thyristors 3 or 4 and the load current passes through the elements 3.6 or 4.5. In emergency operation mode, when the load resistance becomes less than the allowable value, the radiation energy of any of the LEDs 16 or 17 (depending on the polarity of the input voltage) of the optocoupler 14 becomes sufficient to turn on the photo thyristor 15. This photo thyristor shunts the circuit from the resistor 12 and the LED 11. The current through the LED decreases and it turns off. Upon the arrival of the reverse half-wave voltage to the photo thyristors 8.9, they are turned off, and consequently, the thyristors 3 and 4, disconnecting the load from the AC network. The invention The device for protection of an AC power source, containing a current sensor made in the form of a shunt, in parallel with which connected first LEDs of the first optocoupler are connected through the first resistor, the photothyristor of which is connected to a constant voltage source through the second resistor, and the protection executive , made in the form of two opposite-connected thyristors, which are identified by counter-connected diodes, the thyristor cathodes being combined, and in their chains equalizing electrodes include photothyristors of the second optocoupler, whose LED through the third resistor is connected in parallel with the photothyristor of the first optocoupler, characterized in that, in order to increase reliability, it is equipped with a transformer, the primary winding of which is connected to the AC source, and the secondary through the photothyristors of the second optocoupler is connected between thyristor control electrodes.