SU905883A1 - Device for single-phase protection in three-phase electric networks with insulated neutral wire - Google Patents

Description

The device relates to electrical safety and fire protection equipment in electrical networks with insulated or compensated neutral and can be used in any industry, agriculture, transport, construction and communication using electrical systems with an isolated or compensated source neutral.

A device is known that implements the principle of artificially closing a damaged phase to the ground. The device consists of a separate block for searching the faulty phase, a block forming the command for switching on the oil switch, which closes the damaged phase to the ground, a block for disconnecting the electrical installation as a whole, etc., (1,

The disadvantages of the above device include tr, that the functional blocks for selecting the faulty phase, the formation of the switch for switching on the oil switch are not deciphered, therefore it is difficult to judge the efficiency of the circuit as a whole. The device works to shut off, which is not necessary for systems

with an isolated neutral, Under conditions of electrical installations with a voltage higher than 1000 V, even switching off the electrical installation and subsequent shorting of the damaged phase does not guarantee complete electrical safety of the person who is touching and the risk of death is reduced. The closest technical

10 entities for electrical systems with voltages up to 1000 V is a device for protection against single-phase shorting in three-phase networks with insulated neutral, consisting of

15 three maximum voltage relays, the coils of which are connected in series with a capacitor to the phase voltages of each phase with respect to ground. Make contacts

20 overvoltage relays are connected between each of the phases and ground through three pairs of closing contacts of the overvoltage relay. When a single-phase touch or the closing of one of the phases to the earth, the voltage on this phase decreases, and on the OTHERS increases, which leads to the inclusion of two relays of intact phases and short to ground

Claims (2)

) 0 damaged phase and thus. Virtually all current flows past man 2. The downsides of this device are its long response time due to the inertia of the overvoltage relay, which increases the likelihood of a person being electrocuted when the phase is touched, and the need for special overvoltage relays two pairs of make contacts. The purpose of the invention is to increase the speed of the device. The goal is achieved by the fact that the device for protection against single-phase closure in three-phase electrical networks with an insulated neutral, contains a filter block voltage zero sequence; Introduced three symmetrical thyristor, three threshold elements, and the inputs of the filter block voltage zero sequence connected to the corresponding corresponding phases of the control object, the first, second and third outputs of the filter block of the zero sequence voltage are respectively connected to the inputs of the first, second and third elements In comparison, the first outputs of which are connected to the earth bus and to the fourth output of the block F1: Ltra of the zero sequence voltage, the second outputs of the first, second and third threshold elements are connected to control electrodes of the first, second and third symmetrical thyristors, respectively the first terminals of which are connected to the corresponding phases of the control object, the second terminals of symmetric thyristors are connected to the zy-bus. Moreover, the zero voltage sequence filter block contains six resistors, with the first terminals of the first, second, and third resistors respectively connected to the first, second, and third input cells of the zero sequence voltage filter block, the second terminals of the first, second, and third resistors are connected respectively to the first, second and third output terminals of the filter unit with a zero sequence, respectively, with the first terminals of the fourth, the fifth, and the sixth resistor, respectively, the second terminals of the oryh soodineny the fourth output terminal of the filter unit zero sequence voltage inventive device shown in the drawings. The device contains symmetric thyristors 1-3, threshold elements 4-6, made on the basis of direct current amplifiers operating in the key mode, block 7 of the zero voltage post-filter filter; ti. The device works as follows. In the normal operating mode of the network, the signal taken from the outputs of the zero voltage sequence filter block is fed to the inputs of threshold elements 4-6, the output of which does not have a signal, and the control electrodes of symmetric thyristors 1-3 do not receive a signal, i.e. symmetrical thyristors are closed. When a person touches the phase or deteriorates the insulation resistance of this phase below the permissible level, the voltage between the damaged phase and the earth decreases, and on the other two phases it increases. Reducing the voltage between the damaged phase and the ground triggers the threshold element 4, the signal from which goes to the control electrode of the symmetric thyristor 1. Symmetric thyristor 1 opens and bridges the damaged phase to the ground, sucking the almost full current of the single-phase circuit (touching ). At the same time, the threshold elements 5 and 6 included in the intact phases remain in their original state, since they react only to a decrease in the voltage of the phases relative to the earth, and in the intact phases this voltage, on the contrary, increases. When planned grid disconnections and subsequent switching on under voltage at the first moment after switching on the voltage on all threshold elements 4-6 are minimal and equal to zero, therefore, with voltage applied to the network, they could give out pulses for simultaneous opening of all three symmetric thyristors, which would lead to a three-phase short circuit across the earth. To exclude the simultaneous opening of symmetrical thyristors at the moment of turning on the network under voltage, the power supply unit of the threshold device provides for a connection delay. After the malfunction of the damaged phase is eliminated or the person is released from the current-carrying part, voltage is applied to the input of the threshold element 4, and the signal on the control electrode disappears and thus the device returns to its original position. The proposed device is characterized by speed, which is the main indicator in protecting a person from electric shock, ease of manufacture and reliability. The invention 1. Device for protection against single-phase three-phase closure electrical network x with an isolated neutral, containing a zero-sequence voltage filter block, characterized in that, in order to improve the performance of the device, three symmetric thyristors and three threshold elements are inserted into it, and the inputs of the zero-sequence voltage filter block are connected to the corresponding phases of the control object , the first, second and third outputs of the filter unit of the voltage of the zero sequence are respectively connected to the inputs of the first, second and third elements of the comparison, the first the outputs of which are connected to the ground bus and to the fourth output of the zero-sequence voltage filter block, the second outputs of the first, second and third threshold elements are connected to control electrodes of the first, second and third symmetric thyristors, respectively, the first terminals of which are connected to the corresponding phases of the control object The second pins of symmetric thyristors are connected to the earth bus. 2. The device according to claim 1, characterized in that the zero voltage sequence filter unit comprises six resistors, the first terminals of the first, second and third resistors respectively being connected to the first, second, third input terminals of the zero voltage filter unit, the second terminals of the first , the second and third resistors are connected respectively to the first, second and third output terminals of the filter unit of the zero-sequence voltage and the first terminals, respectively, the fourth, S of the fifth and sixth resistors, the second terminals of which are connected to the fourth output terminal of the zero-sequence voltage filter unit. 0 Sources of information taken into account in the examination 1. Industrial Energy, 1977, No. 5, p. 37 - 38. 2. USSR author's certificate 5 per application 2700028 / 21-24, cl. G 01 R 31/02, 27.06,79.