SU1644284A1 - Device for internal fault protection of capacitor bank with grounded neutral - Google Patents

Abstract

The invention relates to relay protection of capacitor banks assembled in a star with grounded neutral. The purpose of the invention is to increase the sensitivity and reliability, as well as to prevent false triggering of the device and timely reduce the damage intensity of the capacitors of the battery with phase-switch actuator when used to protect it. bus voltage transformer The goal is achieved by the fact that the device reacts to the geometric difference of two currents of current zero the length and current of the compensation generated by the zero-sequence voltage by means of a phase-rotation circuit 5 and the transmission coefficient

Description

The invention relates to electric power industry, namely to relay protection technology, and can be used to protect a capacitor bank with a grounded neutral from internal damage.

The purpose of the invention is to increase the sensitivity and reliability, as well as to avoid false triggering of the device and timely reduce the intensity of damage to battery capacitors with a phase-triggered switch when it is turned on and used to protect a bus voltage transformer.

FIG. 1 is a block diagram of the device; in fig. 2 shows the response characteristic of the device with braking.

The device contains a current-voltage converter unit 1, a zero-sequence current filter 2, an adder 3, a voltage conversion unit 4, a phase-rotational circuit 5, a fundamental harmonic filter 6 and 7, a rectifier 8 with a smoothing filter, a measuring instrument 9, AC modulator 10, braking ratio control unit 11, threshold element 12, coarse threshold element 13, logic element 2I 14, time delay element 15, output element 16, element 17 with a return delay.

At the same time, the outputs of current transformers are connected to the input of block 1 of current-to-voltage converters, the outputs of which are connected via variable resistors; with the inputs of the zero-sequence current filter 2, the output of the specified filter is connected to the first input of the adder 3, the second input of the adder 3 is connected via phase-rotation circuit 5 to the output of the zero-sequence voltage conversion unit 4, the output of the adder 3 through the main harmonic filter 6 of the alternating current torus 10 and to the measuring instrument 9, the control input of the modulator, through the braking coefficient control node 11, is connected to the output of the rectifier 8 with a smoothing filter, the rectifier input The cable is connected via the second main harmonic filter 7 to the output of the zero-sequence voltage conversion unit 4, the output of the modulator 10 is connected to the input of the threshold element 12, the output of the threshold element 12 is connected to the first input of the time delay element 15, the second input element 2 and 14 is connected to the output of the element 17 with a delay to return, the input of the coarse threshold element 13 is connected to the output of the 5 nd Los filter 6, and its output, as well as the outputs of the element 2 and 14 and the time delay element 15 cheny to the input of the output member 16 to input member 17 with a delay of return contacts connected

Q relay from the switch control circuit. The control of the element with a return delay is performed using the contact of the “Disabled - RPO” relay or the “On - RKB” command relay. If the time phase difference of the opening phase

5 switches exceeds the response time of the device, then a relay contact of the "Disconnect - CSC" command is connected in parallel with the RPO or RKV contact. This device design ensures that when the switch is turned on, the battery is disconnected without

0 time delays in case of damage in the zone of operation of a coarse organ, and in the dead zone of a coarse organ, with a time delay, which allows for overload capacity of the battery.

This design allows you to perform

5 measuring body reacting to the geometric difference of two currents, the zero sequence current of the battery and the compensation current released from the voltage

zero sequence using a phase-shifting circuit and a transfer coefficient to the summation circuit, which is formed on the adder. For internal damage, these currents are added together, and for external damage they are subtracted, which further increases the sensitivity of the device.

The fundamental harmonic band filter is introduced to detun the unbalances of the free components of the transients and the harmonic components of the network. To eliminate spikes and fluctuations in the output voltage of the bandpass filter, a critical attenuation filter is applied when the input signal is stepped.

In real measuring circuits, there are errors of current transformers, voltages, errors in balancing the summation circuit, etc., which cause the appearance of an imbalance signal at the output of the adder. The maximum unbalance value occurs when the external short-circuits are close, since in this case the maximum values of the adder input signals are subtracted. In order not to tune the response setpoint from the maximum unbalance to increase the sensitivity, the device is braked on an AC modulator, which is controlled by a zero-sequence voltage module.

When the battery phase is shorted to earth, the zero-sequence voltage source at the fault location causes two currents to flow: / 0 into the system and / 0 Å into the battery neutral. At the same time / 0 „, the EUT does not depend on the place of the closure, and its magnitude is equal to the phase current of the battery. The zero sequence voltage at the installation site of the voltage transformer will increase as the damage site approaches the substation tires. Therefore, when the battery phase is shorted to ground between the switch and some intermediate point of the battery phase, the protection will be blocked by zero-sequence voltage, which will lead to its failure. To avoid this, for protection, it is necessary to use current transformers installed on the high side of the battery.

The meter serves to monitor the status of the battery. Measuring the phase of the unbalance signal allows you to determine the phase with degrading parameters and memorize it when the device operates to shut off.

Compensation of operational unbalance is carried out by adjusting the transfer coefficients for the inputs of the zero-sequence current filter.

The transfer coefficient of the first input of the adder has a constant value, and the transfer coefficient of the second input, to which the zero-sequence voltage is applied, can be adjusted. By varying this coefficient, the adder circuit is balanced. The condition for balancing the adder circuit in primary values for the case of an external short-circuit and with a transfer coefficient on the first input equal to one has the following form:

/ / o- / J tfo / (- F) - UoKe- 0, (1)

where lou is the resistance of the battery;

/ o-current zero sequence

through the battery; / o - compensation current;

K. - transfer coefficient for the second input of the adder.

To satisfy condition (1), the value of K must be equal to K 1 / AV- The time delay of the return element must exceed the set value of time delay element 15. The setpoint of the time delay element 15 is taken longer than the time difference between the phase breakers of the switch. Since the set of capacitors in the battery is fulfilled with a margin, and the device reacts to the main harmonic, the actuation current of the coarse organ can be taken to be equal to the rated current of the battery. A differentiator is used as the phase-shifting circuit.

When the device operates without braking, i.e. with a constant transmission coefficient of the modulator, in normal mode the currents in the battery phases are equal, the voltage is symmetrical, therefore the current and voltage at output 0 of filter 2 of the zero-sequence current and voltage conversion unit 4 equal to zero, at the output of the adder 3, the signal is zero. The device is in an unhealthy state.

During the breakdown of the battery section, the current in the damaged phase increases, the current and the zero sequence voltage appear, which from the output of the filter 2 of the zero sequence current and the voltage conversion units 4 through the phase-rotation circuit 5 arrive at the inputs of the adder 3, where 0 they are added up and an output signal appears at the output of the adder. This signal passes through the band-pass filter 6 to the input of the modulator 10 and to the measuring device 9. From the output of the modulator, the signal goes to r - the input of the threshold element 12. If the signal

Bh,

exceeds the threshold, then the output of the threshold element 12 is the command to turn off the battery.

With an external short-circuit with ground, the voltage and current of zero sequence appear, which are fed to the inputs of the adder 3, however, the signal at the output of the adder is zero, since the input currents of the adder are equal, and their phases are opposite, therefore the device is in untreated condition.

5 When the device operates with braking, the external voltage and the zero-sequence current appear through the battery when the external short-circuit fault occurs, their signals are fed to the inputs of the adder 3, the output

An unbalance signal appears on the adder, which passes through the bandpass filter 6 to the input of the modulator 10, which could trigger the device. But this does not occur, since from the output of the voltage conversion unit 4, the zero sequence voltage through the band-pass filter 7 is fed to the input of the rectifier 8, where it is rectified, and through the braking coefficient control unit 11 acts on the control input of the modulator 10, reducing its transmission coefficient, which leads to a deeper device, and automatically rebuilds it from unbalance.

In case of internal damage, the signal of the sum of the compensation current and the zero sequence current exceeds the setpoint of the braking characteristic, therefore the device does not fail due to the introduction of braking. The response characteristic of the device with braking is shown in FIG. 2. The starting point of deceleration, depending on the magnitude of the zero-sequence voltage, can move from zero to O. Shonoch, the movement is made by shifting the zero level of the rectifier and using the nonlinearity of the diode in the node 11 for controlling the braking factor.

The braking coefficient control unit 11 consists of a variable resistor, a diode and a capacitor connected to the output of this unit.

When the device is in operation when the battery is turned on and the bus voltage transformer is used for protection when the switch is off, the RPO contact is closed, so the output of the element 17 with a return delay is "O, which blocks the disconnection command from the organ sensitivity from the output of the threshold element 12 on the element 2I 14 At the moment the switch is turned on, during the non-phase mode for the battery, the output of the band-pass filter 6 is a signal that passes through the modulator 10 to the input of the threshold element 12, which responds sets and sends a signal to one of the inputs of the element 2I 14 to the launch of the element 15 time delay. Since at one input of element 2I there is an "About from input of element 17 with a delay of return, its output signal does not change.

If a damage occurs when the battery is turned on and the current exceeds the rated current of the battery, a rough threshold element 13 is triggered and sends a signal to the output element 16, which acts to turn off the switch.

If the damage is small and the coarse threshold element does not work, the disconnection will occur through the time delay of the element 15 from the sensitive threshold element 12.

In the period from the closure of the third phase of the switch to the response time of the time delay element 15, the set threshold of the coarse threshold element is doubled. But this can be allowed, since this time should not exceed 0.15 s, and the battery can be overloaded by 2 times for 15 periods, i.e. 0.3 s.

If there is no damage when the battery is turned on, then after a delay the element 17 with a delay for returning returns to its original state and at its output appears "1 allowing the disconnection command from the threshold element 12 to pass through the element 2 and 14 without time delay.

When used to protect a voltage transformer connected in parallel with a battery, a coarse threshold organ 13, element 2И 14, time delay element 15, element 17 with a delay for return can be excluded from the circuit, since for protection a partial-phase mode will be similar to external short-circuit mode. In this case, the disable command can be performed directly from the output of the threshold element 12 to the input of the output element 16. In this case, the protection is greatly simplified.

The use of the invention makes it possible to eliminate the possibility of avalanche breakdown of capacitors when the battery is turned on with a phase switch squat and the use of a bus voltage transformer for protection.

Claims (3)

1. A device for protecting a capacitor bank with a grounded neutral from internal damage, containing a block of current-to-voltage converters, the inputs of which are connected to the outputs of the corresponding current transformers, and the outputs are connected via variable resistors to the corresponding inputs of the zero-sequence current filter, in order to increase sensitivity and reliability, as well as eliminate false triggering of the device and timely reduce the damage intensity of the capacitors of the ba arei with phase segregated actuator switch when it is turned on in the case of using the bus to protect the transformer voltage, bandpass filters additionally introduced main harmonics, adder, AC modulator, rectifier with smoothing filter, braking coefficient control unit, measuring device, coarse threshold element, return delay element, logical element 2I, the time delay element, the output element, while the output of the zero sequence current filter is connected to the first input of the adder, the second input of the adder connected via a phase rotation circuit to the output of the zero-sequence voltage conversion unit, the output of the adder is connected to the modulator input of the alternating current and to the measuring device via the first main-pass filter of the main harmonic through the braking factor control unit to the output of the rectifier with a smoothing filter, the rectifier input is connected through the second main harmonic filter to the output of the voltage conversion unit zero sequence Of course, the AC modulator output is connected to the input of the newly introduced threshold element, the output of the threshold element is connected to the first input of element 2I and the input of the time delay element, the second input of element 2I is connected to the output of the element with a return delay, the input of the coarse threshold element is connected to the output the first band-pass filter of the main harmonic, and its output, as well as the output of element 2I and the element of time delay are connected to the input of the output element; Acts of relay switch control circuit. 2. The device according to claim 1, characterized in that, in order to eliminate spikes and fluctuations in the output voltage of the bandpass filter with a step input signal, said filter is made in the form of a filter with critical attenuation. 3. The device according to claim 1, characterized in that, in order to avoid failure during single-phase ground faults of the battery phase near the busbars, the current transducer unit is connected to current transformers intended for installation on the high side of the battery. .. (W 0.1 UMH3U0 FIG. 2