SU1614065A1 - Device for proctection against ground single-phase faults in a.c.mains - Google Patents

Abstract

The invention relates to electrical engineering and is intended to protect electrical networks. The purpose of the invention is to increase the reliability and selectivity of the protection. The first input of the summing amplifier of the adder 12 is supplied with a DC voltage proportional to the current flowing through the transformer of this connection, to another input is the DC voltage of a different sign proportional to its own capacitive coupling current, the value of which is set by setting the corresponding gain factor in the circuit adder 12 at the second entrance. From the output of the summing amplifier, the signal arrives at the threshold organ 13, when the setpoint of which is exceeded, the signal through the relay amplifier 6 is fed to the prohibition element 5, in the absence of a signal at the control input of which from the time delay block 4 it passes to the executive body 7, which disables the connection with damage. 1 hp f-ly, 4 ill.

Description

73

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The invention relates to electrical engineering, in particular, to protection of electrical networks, and can be used in electrical networks with an insulated (neutral neutral) neutral grounded through a resistor.

The purpose of the invention is to increase the reliability and selectivity of the protection.

Figure 1 shows the functional diagram of the device; figure 2 is a functional diagram of the control unit health; FIG. 3 shows device voltage diagrams for the normal mode of the Network; 4 shows the characteristic of the setpoint correction block (the signals are marked with the letter U,.} the block number, the output of which shows the signal - the signal is the index under this letter), j The device contains a transformer 1 (1 zero-sequence sequence, to which connected in series are a voltage converter 2, a trunk unit 3, a time block 4, a prohibition element 5, to one input of which a relay amplifier 6 is connected, and an actuator 7, a zero-sequence current transformer 8 Connected to the series-connected key 9, the primary frequency filter 10, the voltage converter 11. The summing amplifier (adder) 12 and the sub-body 13, the output of which is connected With the input of the relay amplifier 6.

In addition, the device contains a sequentially connected controlled generator | 14, a multiplier 15, and a key 16, the second output of which is connected to the input of the filter 10. The second output of the threshold organ 3 is connected to the input of the controlled generator 14, the controlling input of the key 16 and through the element NOT 17 - with a control input to; switch 9. The second output of the voltage converter 2 is connected to the second input of the adder 12 and through the setpoint correction block 18 to the second input of the threshold element 13. The control unit 19 is also connected to the output of the relay amplifier 6 serviceability to the block 19 - 20. The indicator unit 19 includes kyuntrol serviceability posledo- location atelno connected shaper 21 and the OR gate 22.

The second input of the multiplier 15 is connected to the electrical network (transformer of the power unit of the protection device).

The device works as follows.

In the normal network mode, the output signals of the elements and blocks 1-4 and 8 are equal to zero, the key 9 is open, the key 16 is closed. Controlled generator 14 generates

low frequency sawtooth voltage. Let the period of this voltage be 5 seconds and it goes to one input of the multiplier 15, to the other input of the last the harmonic voltage of 50 Hz from another signal generator, which is used for electrical network, is supplied. As a result, at the output of multiplier 15, harmonic oscillations of amplitude 10 are obtained, whereby the sawtooth law varies from zero to maximum, from maximum to zero, again from zero to maximum, etc. (fig.Z). From the output of the multiplier 15, this complex signal through the closed key 15–16, the filter 10 and the voltage converter 11 goes to one of the inputs of the adder 12, and the signal from the voltage converter 2 arrives at its second input. From the output of the adder 12, the signal arrives at 20 the first input of the threshold organ 13, the second input of which from the set correction unit 18 receives the constant voltage UycT.2 of the setpoint. From the output of the threshold organ 13, the signal is fed to the input of the relay amplifier 25, and from there to the input of the prohibition element 5. To another input of the element 5 of the ban receives a signal from the block 4 time delay. In this case, the actuator 7 is turned off, and pulses arrive at the input of the control unit 19 of the health control 30, as a result of which a voltage appears at the output of the block 19 and the indicator 20 lights up. If there is any disturbance in the circuit, the signal at the output of the relay amplifier 6 35 disappears and the indicator 20 goes off, which indicates a malfunction of the protection device. Thus, in the normal network mode, the health of the protection device is monitored, which significantly increases the reliability of this device.

With a single-phase earth fault, signals are generated at the protected connection at the outputs of transformer 1 and transformer 8, and at the first 45 output of converter 2, the signal is greater than voltage Uyci.i of threshold body 3 and with delay time designed for detuning from transients and provided by the block 50 4 time delay, the prohibition element 5 receives a signal that permits the actuation of the actuator 7. - From the second (inverse) output of the threshold organ 3 also the signal is blocking the controlled generator 14. allowing the switch 16 and through the element NOT 17 - the closing switch 9. The signal from the current transformer 8 through the switch 9 and the filter 10 is fed to the voltage converter 11 and from it via the adder 12 - to threshold

organ 13. If the converted voltage at the output of the adder 12 is higher than the voltage UycT.2 of the setpoint, then the relay amplifier 6 receives a signal which, amplified by the relay amplifier 6 and passing through the prohibition element 5, triggers the actuator 7, as a result, the executive body 7 ensures shutdown of the damaged connection.

Thus, to take into account its own capacitive current, the connections use a summing amplifier (adder) 12, the first input of which receives a direct current voltage proportional to the current flowing through the TNCN of this connection, and the other input - direct current voltage another sign, proportional to the intrinsic current 1 of the connection, as a result of which the difference of the corresponding currents is obtained at the output of the adder 12. The value of the own connection current is set by setting in the circuit the corresponding gain factor of the adder 12 at the second input. The signal 1comp1 is taken from the output of the voltage converter 2. As a result, when the voltage Uo of the neutral changes, the currents (single-phase ground-to-ground) and 1s1 respectively change. but at the same time the ratio between them remains almost constant.

In the case of a single-phase earth fault on an intact connection, the signal at the first input of the threshold organ 13 will be less than the voltage UycT.2 and therefore the output signal of the threshold organ 13 will not change. Consequently, executive body 7 will not change its state, i.e. will not work.

Claims (2)

Claim 1. Device for protection against single-phase ground fault in an AC mains power supply containing a first switch connected to the secondary winding of a zero-sequence current transformer, the first key, the fundamental frequency filter and the first voltage converter, in series connected relay amplifier, the BANNER element and the executive body, to the output of the relay amplifier is connected the input of the health monitoring unit, as well as the indicator first threshold organ connected in series to the second threshold organ and the time delay unit whose output is connected to the permit input of the BAN element, sawtooth voltage generator , the second switch, the transformer of the zero-sequence voltage, which is so that, in order to increase the reliability and selectivity of the protection, it is equipped with a second a voltage converter, a multiplier, a summing amplifier, a setpoint correction unit and an element, and the second voltage converter is connected between the output of the zero sequence voltage transformer and the input of the second threshold element, the inverse output of which is connected to the trigger input of the sawtooth generator input of a second switch connected between the input of the filter and the output of the multiplier, the first input of which is connected to the output of the generator, and the second input is connected to the terminals for Connected to the mains, the first input of the summing amplifier is connected to the output of the first voltage converter, the second input of the summing amplifier is connected to the inverse output of the second voltage converter connected to the input of the setpoint correction unit, the output of which is connected to the installation input of the first threshold element whose input is connected to the output of the summing amplifier, the output of the first threshold organ is connected to the input of the relay amplifier, the control input of the first key is NOT connected to the inverse through the element the output of the second threshold of the body, and the input of the indicator is connected to the output of the control unit health. 2. Device pop. 1, characterized in that the health monitoring unit is made in the form of serially connected long pulse pulses and an OR element, the second input of which is connected to the input of the health monitoring unit. 1 FIG. 3