SU1427463A1 - Arrangement for protection against fault to earth in network with insulated neutral - Google Patents

Abstract

This invention relates to electrical engineering and is intended to protect against earth faults in networks with insulated neutral. The aim of the invention is to increase the sensitivity of the protection. When an earth fault occurs, the input of the amplifier - limiter 1 receives a voltage of 3Up, which is converted at its output into rectangular pulses fed to the input of the former 2 to receive pulses at the moments of changing the sign of voltage 3 Ue and serving to control the gated comparators 4 and 5 , the information inputs of which receive a signal 31e, fed through a low-pass filter. At the outputs of gated comparators, shutdown pulses will be generated in case of internal damage. 3 silt, (L

Description

four

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with

The invention relates to electrical engineering and is intended to protect against earth faults in networks with insulated neutral.

The aim of the invention is to increase the sensitivity of the protection

Fig, 1 shows a functional diagram of the device; FIGS. 2 and 3 are signal plots explaining the operation of the skeme.

 The device contains an amplifier-processor, a driver 2, a low-pass filter 13, gated comparators 4 and 5, a response body 6, a zero-sequence current sensor 7, a zero-sequence voltage sensor 8.

Limit amplifier input 1. is connected to the output of the zero-sequence voltage sensor 8, and the output is connected to the input of the imager 2, the output of which is connected to the gate inputs of the comparators 4 and 5, the input of the low-pass filter 3 is connected to the output of the zero-sequence current sensor 7, and the output is connected to the information inputs of the comparators 4 and 5, the input of the reacting authority 6 is connected to the outputs of the comparators 4 and 5,

Fig. 2 shows plots 9-13 in Fig. 3, and plots 14-18 of signals illustrating the operation of the protection device in an intermittent arc circuit. In FIGS. 2 and 3, the following notation is adopted: 3Uo, 31o — voltage and current of the zero-sequence sensors; and - the output voltage of the amplifier-limiter; U (f is the output voltage of the driver 2; V is the output voltage of the low-pass filter 3; UK is the output voltages of the first and second 1cmparators, respectively.

The operation of the device with a metal circuit to earth.

Protection works as follows. When a ground fault occurs, the input of the amplifier-limiter 1 receives a voltage of 3Uo, which is converted at its output into direct impulses with steep fronts - UKO. The voltage enters the input of the imager 2, at the output of which short pulses U "p at the moments of changing the sign of the voltage ZI,

five

It can be seen from FIG. 2 that free zero-sequence currents occur at the time of the closure, due to the metering of capacitances of the intact phases, the maximum possible frequency of which is 3 kHz, therefore it is advisable to ensure reliable operation of the first half of the free current wavelength gating pulses U with a duration equal to the minimum possible half-period of free current

 , t, e, the parameters of the imager should ensure the formation of gating pulses Uep with a duration equal to tnp 4 2 / sbts 0.15-16 s. A zero-sequence current is fed to the input of the low-frequency filter 3. Filter 3 must have a cut-off frequency of 3 kHz to suppress the high-frequency harmonics of the discharge of the capacitance of phase damage. The voltage and rnc from the output of the low-pass filter 3 goes to the information inputs of comparators 4 and 5, the short pulses go to the gate inputs of which. The first gate of the comparator 4 generates a logical signal U at the output as follows:

1 if ifnch O and Ucp Uftoe; Oh if ifz Oh and and

0

five

0

five

0

where is uitop

p Uno i

UK, I Oh, j if ifnch 0 and Ucp - threshold of sensitivity

comparator 4 on the gate input.

The second gated comparator 5 generates a logic signal U ((. J as follows:

if a

if ifph

O and Uqp Unov

n and Unep

. O and Uop;

where Ufvop is: - sensitivity threshold of .comparator 5 at the gate input,

Gated comparators can be implemented on the basis of operational amplifiers, for example, 140UD 12 or 1407UD2 or gated comparators 521СА4,

It can be seen from FIG. 2 that the signals U "and UK, equal to a logical unit, are formed only in the case of internal damage. Moreover, a logic signal equal to one, in the case of an internal circuit, appears at the input of the reacting body at the first moment of the circuit, or more precisely during the first half period of the free current of the Split sequence, Backward in the appearance of the leading edge of one of the signals equal to the logical unit It only determines the delay in the current channels and the voltage and h is the fraction of the half-period of the free current, i.e. The proposed device has potentially very high speed, and allows you to generate a tripping pulse in 15 times more than 0, G5 1 (,

Fig. 3 shows signal plots explaining the operation of the proposed protection under an intermittent arc circuit, for the case where the breakdown 20 occurs at the maximum phase voltage, and the arc extinguishes on the first passage through the zero of the free, discharge current and capacities of the intact phases.

From FIG. 3 it can be seen that in this case, during the first half-period of free current, if an internal fault occurs, a tripping impulse is generated at the protection output

The proposed device does not contain a low-pass filter voltage in the channel, and the cut-off frequency of the filter

Claims (1)

in the current channel rdv a 3 kHz, i.e. 50 Hz, which provides for the formation at the inputs of the comparators with an arc circuit of signals that are much larger in amplitude compared to the device-prototype and significantly increases the sensitivity of protection. Invention Formula A device for protection against earth faults in a network with an insulated neutral, containing a zero-sequence voltage sensor, an amplifier-limiter whose output is connected to the input of the driver, a zero-sequence current sensor whose output is connected to the input of a low-pass filter, and a response organ that differs from the fact that, in order to increase the sensitivity, the first and second gated comparators are additionally introduced into it, the outputs of which are connected to the input of the reacting authority, the information inputs Comparator bridges are connected to the low-frequency output and the comparators gating inputs are connected to the output of the former, the input of the limiting amplifier is connected to the output, the zero-sequence voltage sensor ten eleven UK ,  and „or Ua f uxt land. nn (/ " and. (/ "/ fi.Z