SU1201945A1 - Device for automatic shutting of faulted phase in isolated neutral system - Google Patents

Abstract

AUTOMATIC DEVICE J. BYPASS faulted phase in an electrical network with isolated neutral, comprising: a voltage sensor in the form of a transformer, the two secondary windings is connected to a selection unit the faulty phase, the output of which is connected via a control unit to switch the three shunt m ,, each phase conductor connected to A star, characterized in that, in order to increase the selectivity of the device, a current sensor is inserted in it, which is installed between the zero point of the star of the bypass switches and the ground the unit forming an alternating voltage directly proportional to the current flowing through the shunt switch, the unit generating the alternating voltage directly proportional to the bias voltage of the neutral and shifted relative to it in phase, the rectifier, the threshold organ, the holding organ and an actuator, wherein the output of the current sensor is connected through a block forming an alternating voltage directly proportional to the current flowing through the shunt switch with the first rectifier input and the first output block a, od (Oh. variable voltage, directly proportional to the neutral bias voltage and shifted relative to it in phase, the input of which is connected to the second winding of the voltage sensor, the output of the said rectifier through the series-connected threshold organ, optaH time delay, the actuator is connected to each of the shunt-disconnecting switches, and the second output of the SP block, which generates an alternating voltage, is directly proportional to the bias voltage of the neutral and shifted relative to it in phase, of the connections to the second input of the rectifier.

Description

This invention relates to electrical engineering, in particular, to electrical safety equipment in electrical networks with insulated neutral.

The purpose of the invention is to increase the selectivity of the device.

The drawing shows the blkk-scheme of the proposed device.

The device has shunt switches. 1., i control block 2, Damaged phase selection block 3, forming an alternating voltage directly proportional to the current flowing through the shunt switch, block 5 forming an alternating voltage directly proportional to the bias voltage of the neutral and shifted relative to it in phase, rectifier 6, threshold organ 7, time-delay organ 8, actuator 9, current sensor 10 and voltage sensor 11. .

The damaged phase selection unit 3 is connected to the secondary three-phase winding of the voltage measuring sensor and to the secondary winding of the same sensor connected in an open triangle circuit. The selection of the damaged phase is made by increasing the voltage in the advanced phase with control by the bias voltage of the neutral.

The block for selecting the faulty phase outputs control signals to the control block 2.

Control unit 2 implements the following operation algorithm:

- after the occurrence of a time ground fault in the network, it issues a command to turn on the shunt phase switch with damaged insulation selected by block 3;

-after turning on the shunt switch with time delay issue: em command to turn it off;

- if the ground in the network is not eliminated (block 3 exerts a control signal about the closure of the corresponding phase), issues a command to re-enable the shunt switch.

Such an operation algorithm is explained as follows.

Since the analysis of the number and duration of single-phase earth faults in networks of 6–10 kV showed that about 80% of them are of a passing nature and self-extinguish over time

up to 5 s, then for detuning from passing closures, it is advisable to bypass the damaged phase with a time delay after the earth's appearance.

After shunting the damaged phase, a certain part of the closures, especially the arc ones, is eliminated within 1-2 s. If, after this time, the shunt switch is turned off, it often happens that there is no earth. Therefore, in the device for automatic shunting of the damaged phase (ASF), it is advisable to enter

test cycle: shutdown through

2c power switch, automatic checking for earth presence

with the subsequent switching on of the shunt switch, if the earth is still

there is a network, and a return to the original state in the absence of land.

The device control unit 2 consists of three time relays connected in series. The first relay is;

triggered by input from the block

3 and with a time delay, it gives the command to turn on the shunt switch. The second relay, triggered by the output signal of the first time delayed relay, gives a signal to turn off the shunt switch. The third relay, triggered by the output signal of the second relay, supplies a signal to re-enable the shunt

switch, if the earth in the network does not disappear.

The control unit is implemented on electromagnetic relays or semiconductor elements.

Shunt switches 1. With phase control are known power switching devices designed for operating voltages and mains currents. They can be oil, vacuum, thyristor, or other types.

One of the contacts of the shunt switches is connected to the corresponding phase of the network, the other is connected to the ground loop through a common current sensor. The operation of turning on and off of these switches is carried out according to commands issued by control unit 2. In addition, the shutdown of any of the included shunt switches can be carried out by a command issued by the executive body 9.

The unit 4, which forms an alternating voltage, is directly proportional to the 3. current flowing through the bypass switch and is connected to the current sensor 10. It contains an intermediate transformer, the secondary winding of which is loaded onto a resistor. In connection with the fact that the earth fault current of a network with an isolated neutral contains higher harmonic components of the industrial frequency, in order to limit these components in the output voltage, block 4 contains a filter with a resonant frequency equal to industrial (50 Hz) . The unit 5, which forms an alternating voltage, directly proportional to the neutral bias voltage and rotated relative to it in the angle, is connected to the secondary winding of the voltage sensor 11 connected in an open triangle pattern. It contains an intermediate transformer, resistors, phase-shifting chain. The outputs of blocks 4 and 5 are connected in series to and connected to rectifier 6. As a result, the rectifier is supplied with a voltage equal to the difference between the output voltages of blocks 4 and 5. When grounding in the network with an insulated neutral, the capacitive circuit current is With a neutral bias voltage, the angle is close to 90 °. The block 5 rotates the voltage proportional to the voltage of the zero sequence by the same angle until it coincides in phase with a voltage proportional to the circuit current and coincides with it in phase, which is formed by the block 4. Therefore, the rectifier 6 is supplied with voltage Close to zero This is achieved by pre-adjusting the output voltages of blocks 4 and 5 with the shunt switch on one of the phases turned on and there is no ground in the other point of the VII circuit of the network. If a portion of the load current flows through the current sensor 10 in addition to the capacitive current of the network, they are geometrically added. The total current through the ASF is, with the neutral bias voltage, an angle other than 90 °. Different from the capacitive and the amplitude of the total current. Therefore, the rectifier supplies a voltage proportional to 45 of that part of the load current of the damaged line that flows through the shunt switch to the fault site. Rectifier 6 is a known full-wave bridge rectification circuit. To the output of the rectifier 6 is connected the threshold body 7, performed on the operational amplifier. To the output of the threshold body 7 is connected to the body 8 lag time. Its purpose is to tune up from surges in the load current of the line that occur when starting powerful electric motors, connecting transformers, etc. The time delay organ 8 is designed as a time relay on the operational amplifier, which is triggered after the capacitance has been charged after the transistor has deactivated it. An output unit 9 is connected to the output of the time-losing organ 8, which is an electromagnetic relay controlled by a transistor switch. When the relay contacts are closed, a command signal is issued to switch off the bypass switches. When the faulty phase is bypassed, the network mode does not change in terms of linear voltages, the power supply to consumers is not interrupted. As a result of shunting, the voltage relative to the earth in a phase with damaged insulation is significantly reduced, successful ground current arcs are extinguished, and the voltage of touch and pitch at the site of damage is significantly reduced. During the operation of the ASF devices with many positive characteristics, it was observed that in some cases when shunting, instead of reducing the voltage, it increased in the circuit. The analysis, calculations, and specially performed experiments showed that this phenomenon is related to the flow of a portion of the load current through a shunting circuit through a shunt circuit breaker - the place of damage under the effect of a voltage drop in the line resistance. This phenomenon is observed only at low transient resistances at the point of closure, when the total resistance of the shunt circuit is comparable with the resistance of the LINE wires (closures at grounded supports, consumer substations of 6-10 / 0.38 kV, supports with disconnectors, arrays and t .d.) If the plugging is caused by insulation damage on ungrounded reinforced concrete supports (of which more than 70% are in the network) or wire breakage with its fall, then due to the large transitional part of the ground flow resistance, no load current occurs. Shunting of the damaged phase here causes a significant reduction in voltage at the site of damage. The device works as follows. When grounding to one of the phases of a three-phase electrical network e with an isolated neutral, the block of the choice of the damaged phase 3 45 determines the damaged phase and supplies the signal to the control unit 2, which in turn gives the command to turn on the shunt switch 1 of this phase. In the absence of a portion of the load current flowing through the switching-on bypass switch, the voltage at the input of unit 7 from unit 6 is below the pickup setting. If a portion of the load current flows through the shunting circuit, in addition to a capacitive closure current, a voltage appears at the output of rectifier 6, which triggers the threshold organ 7 and, respectively, organs 8 and 9. The actuator 9 triggers shunt switch.

Claims (1)

DEVICE FOR AUTOMATIC BYPASSING OF A DAMAGED PHASE IN AN ELECTRIC NETWORK WITH INSULATED NEUTRAL, containing a voltage sensor in the form of a transformer, to the two secondary windings of which is connected a fault phase selection unit, the output of which is connected through the control unit to three bypass switches connected to each phase wire, characterized in that, in order to increase the selectivity of the device, a current sensor is inserted into it, installed between the zero point of the star of the bypass switches and the ground, a lock generating an alternating voltage directly proportional to the current flowing through the shunt switch, a block generating an alternating voltage directly proportional to the neutral bias voltage and phase shifted relative to it, a rectifier, a threshold organ, a delay element and an actuator, while the current sensor output is connected through the block forming the alternating voltage directly proportional to the current flowing through the shunt switch, the first input rec- _e DC converter and the first output unit, with a shape ® alternating voltage directly proportional to the neutral bias voltage and phase shifted relative to it, the input of which is connected to the second winding of the voltage sensor, the output of the specified rectifier through a series-connected threshold organ, time delay element, an actuator connected to each of the shunt switches, and the second output of the unit forming an alternating voltage, directly proportional to the neutral bias voltage and phase shifted relative to it, is connected to the other input of the rectifier. SU, .., 1201945> t