SU1598015A1 - Ground leak current protection device for electric networks - Google Patents

Abstract

This invention relates to leakage current protection devices in electrical networks with insulated neutral, including thyristor converters. The aim of the invention is to improve the reliability and noise immunity of the device. In the presence of leakage resistance 15, a circuit is created for passing an operational current — an operational voltage generator, leakage resistance 15 and a load resistor 9. Through the electronic switch 8, which opens synchronously with the switching on of the first amplifier 4, through the second amplifier 10, the voltage from the resistor 9 is fed to the input the integrator 11. Due to the fact that the switch 8 and the amplifier 4 are switched synchronously, the average value of the voltage at the integrator output is positive. This voltage characterizes the leakage current and, if it is greater than the threshold value, the relay element 13 and the display unit 12 are triggered. The use of the device makes it possible to control the occurrence of leakage currents in electric networks with thyristor converters. 1 il.

Description

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This invention relates to leakage current protection devices in electrical networks with insulated neutral, including thyristor converters.

The purpose of the invention is to improve the reliability and noise immunity of the device.

The drawing is a schematic diagram of the device for protection against earth leakage currents.

The device contains a capacitive filter connection of capacitors 1 connected to the wires of an alternating voltage network, capacitors 2 connected to the poles of the rectified voltage, limiting resistors 3, first amplifier 4, driver 5 rectangular pulses, trigger 6, block 7 galvanic isolation, electronic key 8, the load resistor 9, the second amplifier 10, the integrator 11, the display unit 12 and the output relay element 13.

Capacitors 1 are connected to phases A, B, and C of the network, and capacitors 2 are connected to the output poles of the controlled rectifier 14.

Resistors 3 limit the current flowing through the coupling capacitors between the supply and the rectified voltage sources. Resistors 15 are equivalent to earth leakage resistance.

A shaper 5 rectangular pulses, a trigger 6, a block 7 of galvanic isolation and a first amplifier 4 form an operational voltage generator with a frequency of 25 Hz. The key 8 serves to connect the load resistor 9 to the integrator input through the second amplifier 10, the purpose of which is to amplify the leakage current signal, weakened by the introduction of limiting resistors 3 into the measuring circuit.

The device works as follows.

When the supply voltage and the voltage of 50 Hz are turned on at the input of the circuit, block 5 forms rectangular pulses with a frequency of 50 Hz. These pulses are fed to the counting input of trigger 6, at the output of which pulses with a frequency of 25 Hz are formed, which are rigidly connected to the network. Through a galvanically isolated block 7, these pulses are fed to the first amplifier 4, from which output through limiting resistors 3 and capacitors 1 and 2 connections overlap the network pins. In the presence of leakage resistance 15, a circuit is created for the passage of an operational current: an operational voltage generator (4,5,7,9) a leakage resistor 15 and a load resistor 9.

Through the electronic switch 8, which opens synchronously with the switching on of the first amplifier 4, through the second amplifier 10, the voltage from the resistor 9 is fed to the input of the integrator 11. In connection with the fact that the switch 8 and the operating current source are switched synchronously, the average value of the output voltage the integrator is positive when the key switching frequencies coincide 8

and amplifier 4. This voltage characterizes the leakage current to earth. If it exceeds a predetermined threshold voltage set by the output relay element 13, the latter triggers and shuts off the source of the mains voltage. In parallel, this voltage is applied to the display unit 12.

If the load resistor 9 contains signals of interference generated by the network voltage of 50 Hz or rectified voltage with a frequency multiple of the network frequency, an equal number of positive to negative half-voltages is supplied to the integrator input. As a result, the voltage on the integrator due to interference during the measurement time is zero.

Thus, the use of the proposed device makes it possible to control the occurrence of leakage currents in electric networks with thyristor converters 0 liters. In contrast to the known, the proposed device allows to increase the reliability and noise immunity of protective equipment. A device for protection against earth leakage currents in an electrical circuit can be made using known anneals. A null organ can be used as a former, for example, on the basis of an operational amplifier. A second amplifier and an integrator can also be implemented on the basis of operational amplifiers. As a trigger, you can use any trigger in the integrated design with a counting input, the electronic key can be assembled on an integral switch, for example, type K56iKT3. The first amplifier can be assembled on transistors.

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Claims (1)

Invention Formula Device for protection against leakage currents to earth in the electrical network, containing a capacitive filter connection, the first 0 capacitor terminals of which are connected to the terminals for connecting the AC and rectified voltage to the mains phases, the galvanic isolating unit and the first amplifier, the square pulse shaper, the integrator and the output relay element connected in series, an electronic switch connected by the first input to the phases the first terminal of the load resistor and with a terminal for connection to ground, the second terminal of the load resistor is connected to the common 0 by a wire to which the second inputs of the electronic key, the integrator and the first amplifier are also connected, characterized in that, in order to increase reliability and noise immunity, a trigger, a second amplifier, two limiting resistors and a display unit are added to it, and the input of the driver square impulses connected to the terminals for connection to the phases of the network, and the output - to the score515980156 The trigger input, the output of which is connected to the display unit, is connected to the input of the unit by galvanic development. The input of the second amplifier is connected to the cover and the control input by the electronic wire, the output is first amplified, key, the output of which through the second amplifying through limiting resistors is connected The cable is connected to the integrator input, at the second terminals of the capacitors.