SU1742927A1 - Device for protection against one phase short-circuit to ground in a c network - Google Patents

Abstract

Use: networks with isolated, compensated neutral and neutral, grounded through a high impedance resistor. SUMMARY OF THE INVENTION: To improve the reliability and selectivity of protection, a higher harmonic current channel was inserted into the device, containing 14 higher harmonics filter, rectifier 15, summing amplifier 16, threshold organ, time delay unit 18, and introducing a channel that takes into account higher harmonics of its own capacitive current at each connection, having a filter of 19 high harmonics and a voltage converter 20. 1 hp f-ly, 3 ill.

Description

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The invention relates to electrical engineering, in particular, to the protection of electrical networks, and is intended for operation in electrical networks with an insulated, compensated neutral and neutral grounded through a high impedance resistor.

A device for signaling single-phase earth faults of the type USZ-ZM is known.

The drawbacks of the device are the instability of the output signal with a stable single-phase short circuit to ground (033) and the difficulty of identifying information during arc short circuits to the ground.

Closest to the present invention, there is a device for protection against single-phase ground fault in an electrical AC network, comprising a series-connected first voltage transmitter, a threshold element, a time delay unit, a prohibition element and an actuator connected in series with a zero-sequence voltage transformer. to the transformer then zero sequence the first key, the filter of the main frequency, the second voltage converter, summing amplifier, second threshold unit, relay amplifier, control unit and indicator, output of relay amplifier is connected to the second input of the inhibit element, connected in series to the control output generator, multiplier and second key connected to the input of the fundamental frequency filter, element NOT connected between the control inputs of the generator and the first key, the unit correction unit connected between the second output of the first voltage converter and the second input of the second threshold The second input of the multiplier is connected to the mains voltage, the control input of the second switch is connected to the control input of the generator, the second input of the adder is connected to the input of the set correction unit.

The disadvantages of this protection device are the lack of blocking of the current channel during arc faults to ground and unsuitability

for operation in compensated networks.

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The purpose of the invention is to increase reliability and selectivity by blocking the current channel during transients during ground faults.

Essential features of the invention include serially connected first harmonic filter, a third rectifier, a second summing amplifier, a third threshold organ, and a second time block, which are connected in series a second harmonic filter, and a voltage converter connected to the device.

The time delay blocks are designed to delay the change in their output signals (to offset from

transients) and can be performed, for example, on logic (digital) microcircuit pulse counters of the type K5b1 IE 5. Each time block contains two series-connected pulse counters and a square pulse generator, the output of which is connected to the counting inputs of both marked counters. Each pulse counter of the time delay block has 3 inputs. The main entrance is: installation (the second input is the counting and the third blocking).

When a logical unit is applied to the R input, the counter is set to the null left state (its logical zero is output) and does not respond to the counting pulses. When a logical zero is applied to the R input, the counter calculates the input counting pulses and, with a certain number of them, a logical unit appears at its output, which, acting on the blocking input, prevents the input pulses from counting. The counter remains in this state until a logical unit arrives at its R input. The element of the ban can oyt made in the form of a logical element I.

The summing amplifier is covered by bone feedback and provides for the selection of constant component signals from incoming signals at its inputs, i.e. the output of the summing amplifier is determined by the constant components of its input signals. The fourth rectifier is designed to take into account its own capacitive current (main harmonic)

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protected attachment. The second filter of higher harmonics is also intended to take into account the intrinsic capacitive current of the higher harmonics of the protected connection.

Signals of different signs arrive at different inputs of the summing amplifier. Therefore, at 033 on the other connection, the signal at the output of the summing amplifier will be close to zero. At 033, at the protected attachment, the signal on the main input of the first summing amplifier will be significantly larger than on the second input (when the compensation is detuned), and then the output signal of the summing amplifier will be positive and exceed the setpoint of the second threshold organ, or at the resonant compensation setting (or close to it) the input signals of the first sum of the amplifier can be close in magnitude, and therefore the output signal of this amplifier will also be close to zero. When the neutral voltage varies, the input signals of the summing amplifier also vary in proportion.

The voltage converter is designed to rectify the input voltage and convert it to a DC voltage, i.e. allocation of a constant component proportional to the input signal.

The presence of the second harmonic filter and the voltage converter connected in series allows the output of the latter signal (DC voltage) to be proportional to the current of the higher harmonic parts of the protected connection and proportional to the changing level of the higher harmonics of the ground fault current.

FIG. 1 shows the functional set of 45

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3, the extracting unit k, the prohibition element 5, the relay amplifier 6 and the actuator .7. The secondary winding of the zero-sequence transformer 8 is connected in series with amplifier 9, second rectifier 10, first summing amplifier 11, second threshold organ 12 and logic element OR 13, the output of which is connected to the second input of prohibition element 5.

The secondary winding of the zero-sequence transformer 8 is also connected in series with the first filter I high harmonics, the fourth rectifier 15, the second summing amplifier 16, the third threshold element 17, the second time-delay unit 18, the output of the latter connected to the second input of the OR 13 logic element.

A second filter 19 of higher harmonics and a voltage converter 20 are connected to the input of the first rectifier 2, the output of which is connected to the second input of the third threshold organ 17. A third rectifier 21 is connected between the input of the first rectifier 2 and the second input of summing amplifier 11.

Block k or 18 of the time delay (Fig. 2) contains serially connected first 22 and second 23 pulse counters. The generator output 5 2k rectangular pulses is connected to the counting inputs of the counters 22 and 23 pulses. The output of each pulse counter is connected to its blocking input.

A 2k generator. Pulse-angle pulses for blocks k and 18 time delays are advisable to use one. An amplifier 9 in the current channel of the protection device is installed for convenience

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on the device circuit of protection against single-phase earth faults; 2 is a functional block timing scheme; FIG. 3 is a voltage chart for earth fault on the protected connection; a - with detuning compensation; S - npvt resonant tuning compensation.

A transformer 1 of the zero-sequence voltage is connected to the electrical network (Fig. 1). It is connected in series with the first rectifier 2, the threshold body

amplification of a signal proportional to the current 1O. In the normal network mode, the zero sequence voltage Uo is low and the output signals of the first 3, second 12 and third 17 threshold organs, first b and second 18 time delay blocks, logical element OR 13, prohibition element 5 and relay amplifier 6 is zero. The output signals of the first counters 22 pulses of blocks k and 18 time delays are equal to a logical one.

Let 033 occurred on the protected connection and there was a mismatch of compensation on the network. Then, rectified by the second rectifier 10 of the voltage supplied to the first input of summing amplifier 11, will exceed in absolute value the voltage coming from the third rectifier 21 to the second input of this summing amplifier. The output signal of the latter through the second threshold organ 12, the logical element OR 13 is the prohibition element 5, the relay amplifier 6 is fed to the executive body 7, which is triggered and gives a signal to disable the damaged connection

With a resonance or close to it compensation setting, the signal at the output of summing amplifier 11 is equal to zero, since the residual current contains a small component of the fundamental frequency and usually a significant level of higher r harmonics. In this case, the filter 1 isolates the higher harmonic voltage, and the rectifier 15 rectifies this voltage. The latter is compared with the voltage UJTQ supplied by the voltage converter 20. This voltage is determined by the intrinsic capacitive current of the higher harmonics of the protected connection. Therefore, the voltage and positive impulses appear at the output of the threshold organ 17. They set the counter 22 pulses of the second time delay 18 unit to the zero state and the second counter 23 pulses start counting the time delay ut After this, the voltage at the output of the counter 23 pulses (block 18) is equal to the logical unit and the signal through blocks 13, 5 and 6 enters the executive body 7, which disables the damaged connection. With a time delay Ut.ut4, the counter 22 of the second block 18 time delay sets the counter 23 to zero state.

At 033 outside the protection zone (at the other end), the own capacitive current flows through the current transformer 8. The components of the fundamental frequency and higher harmonics are insignificant and therefore the voltage on the main (the first input of summing amplifier 11 is close in magnitude to the voltage arriving at its second input. Therefore,

the output of this amplifier is 11 voltage

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close to zero. The voltage (level of higher harmonics) at the main input of summing amplifier 16 is approximately

equal to the voltage at the output of the converter 20 (at the second input of the amplifier 16). Therefore, at the output of the amplifier 17, the signal is approximately zero and less than the set voltage, i.e. at the second input of the threshold organ 17. The output signal of the threshold organ 17 is zero. Therefore, the executive body 7 does not work.

When the offset is compensated in the remaining current, the fundamental harmonic becomes significant. In this case, the output channel of the first 14 high harmonic filter may contain the main frequency and it is not always possible to obtain information on 033 through this channel of the higher harmonics. In this case, information on 033 is transmitted through the main harmonic current channel (blocks 9-12). In the case of resonant tuning of compensation, information about 033 comes only through the current channel of higher harmonics (blocks H-18).

Introduction to the protection device of two current channels that react to the main harmonic and higher harmonics of the earth fault current, as well as the introduction of a lock into the last channel, can significantly increase the device selectivity during arc faults to earth and ensure it

5 application in networks with insulated, grounded through a high-resistance resistor and a compensated neutral.

The effectiveness of blocking the current channel at 033 is explained by the fact that, for arc faults to ground, blocking only by the neutral voltage does not always exclude the false actions of the protection device.

Claims (2)

1. Device for protection against single-phase ground fault in an AC mains supply containing series-connected first rectifier connected to a transformer, zero sequence voltage, threshold organ, time delay block, prohibition element, 5 relay amplifier and executive element connected to the output zero sequence current transformer connected in series 0 0 0 917 the amplifier, the second rectifier, the first summing amplifier and the second threshold organ, the third rectifier, the input of which is connected to the output of the transformer of the zero-sequence voltage, and the output to the second input of the first summing amplifier, increase the reliability and selectivity by blocking the current channel during transient processes and taking into account the higher harmonics of the own capacitive current of the protected connection, in it sequentially connected connected to the secondary winding Ke of the current transformer of the zero sequence of the protected connection, the first filter of higher harmonics, the fourth rectifier, the second summing amplifier, the third threshold organ, the second block soak ki time and logical element OR, serially connected second harmonic filter and voltage converter connected between the input of the first rectifier and the second input of the second summing amplifier, the output of the second threshold element connected to the second input of the logical element OR, the output of which is connected to the second input element of the ban. 2. The device according to claim 2, wherein the time delay block comprises two pulse counters connected in series, as well as a generator of right angle pulses, the output of which is connected to the counting inputs of said pulse counters, the output of each pulse counter being connected to its blocking input. Fie.2 a) Vj 1PGPG FIG. 3 f)