What is recloser(Vacuum Circuit Breaker)?

Overview

In the power system, transmission lines are the components with the most failures. Therefore, how to improve the reliability of transmission lines is of great significance to the safe operation of the power system.

The nature of transmission line faults is that most of them are transient faults, accounting for about 80% to 90% of the total number of faults. Most of these transient faults are caused by insulator surface flashover caused by lightning, line discharge to tree branches, and line collision caused by strong winds. These faults are caused by objects such as birds, branches falling on the wires, and surface contamination of the insulator. After the circuit breaker is disconnected by the relay protection action, the fault point becomes free, the arc is extinguished, the insulation strength is restored, and the fault is eliminated by itself. At this time, if the circuit breaker of the transmission line is closed, the power supply can be restored, thereby reducing the power outage time and improving the reliability of the power supply. Of course, transmission lines also have a small number of permanent faults caused by downed poles, short wires, insulator breakdown or damage, etc. These faults still exist after the line is disconnected. At this time, if the circuit breaker is closed, the circuit breaker will be disconnected again by the relay protection action.

It can be seen from the nature of transmission line faults that the possibility of success is quite high if the line is disconnected and then reclosed. Although this closing can be done manually, the effect is not good due to the long power outage. Very significant. For this reason, an automatic reclosing device is used to put the cut line back into operation to replace our manual closing.

After the reclosing is installed on the line, the reclosing itself cannot determine whether the fault is instantaneous. Therefore, if the fault is instantaneous, the reclosing can succeed; if the fault is permanent, the relay protection will operate again to open the circuit after reclosing. The circuit breaker tripped and the re-closing failed. Operational practice shows that the success rate of line reclosing is about 60% to 90%. It can be seen that the benefits of using automatic reclosing are considerable.

The use of automatic reclosing on transmission lines not only improves the reliability of power supply, but also improves the stability of parallel operation of the system and the transmission capacity of the line. It can also correct problems caused by poor structure of the circuit breaker itself, misoperation of relay protection and accidental collision . False trip. Automatic reclosing is widely used in power systems because of its low cost, reliable operation and great effect. However, the use of automatic reclosing will also have some adverse effects on the power system. For example, when reclosing occurs with a permanent fault, the system will be impacted by short-circuit current again, which may cause system oscillation; at the same time, the working conditions of the circuit breaker will deteriorate.

The reclosing of transmission lines can often be divided into single-phase reclosing, three-phase reclosing and comprehensive reclosing; or it can be divided into one-action reclosing and two-action reclosing; it can also be divided into single-side power reclosing and double-sided power reclosing. In addition, it can also be divided into mechanical, electrical and transistor reclosing .

automatic reclosing device should meet the following basic requirements:

1. Automatic reclosing can be started based on the principle that the position of the control switch does not correspond to the position of the circuit breaker.

2. When the circuit breaker is disconnected with a control switch or a remote control device, or when the circuit breaker is placed on a faulty line and is immediately disconnected by a protective device, the automatic reclosing shall not operate .

3. In any case, the number of automatic reclosing actions should comply with the predetermined regulations.

4. The automatic reclosing action should automatically reset.

5. Automatic reclosing should be able to accelerate the action of relay protection after reclosing. If necessary, it should also be able to accelerate its action before reclosing. When closing with a control switch, measures should be taken to accelerate the action of relay protection.

6. When the circuit breaker is in an abnormal state that does not allow automatic reclosing, the automatic reclosing should be blocked.

“Ten questions” about reclosing gates

What is the automatic reclosing device?

automatic reclosing device is a device that automatically switches the circuit breaker back on as needed after the circuit breaker trips due to line fault protection action.

2: Why should we install automatic reclosing device ?

About 90% of the faults on overhead transmission lines are transient faults. After the relay protection action cuts off the transmission line, the short-circuit current disappears and the insulation level of the air will return to the level before the fault. If the automatic The reclosing device can re-close the circuit breaker to immediately resume operation of the line, ensuring the safety and stability of the system.

What are the automatic reclosing methods?

1

Overall weight:

For single-phase faults, single-phase coincidence will cause three-phase jumps after coincidence with a permanent fault; for inter-phase faults, three phases will jump, and three-phase coincidence will cause three-phase jumps after coincidence with a permanent fault.

02

triple:

Any type of fault will jump three phases, three phases will jump after coincidence, and three phases will jump after coincidence permanent fault.

03

Single:

Single-phase fault, single-phase coincidence, three phases will jump after coincidence permanent fault. Phase-to-phase fault, three phases do not overlap after tripping.

04

Disable:

Any fault will jump three phases without overlapping.

Reclosing is divided into single reclosing and multiple reclosing. China basically adopts single reclosing. Circuit breaker reclosing of 110kV and below are three-phase reclosing. At voltages of 220kV and above, circuit breakers have phase-divided tripping . Therefore, there are single-phase reclosing, three-phase reclosing and comprehensive reclosing. Different operating conditions require different reclosing methods to be selectively adopted.

4: What are the starting methods of automatic reclosing?

01

The position does not correspond to the starting mode

After the trip relay operates (TWJ=1), it proves that the circuit breaker is in the off position. If the control switch is in the closed state at this time (KKJ=1), it means that the circuit breaker has been in the closed state before. The method of corresponding start reclosing is called position non-corresponding start reclosing.

This method can not only start reclosing after the circuit breaker is tripped by the protection, but can also start reclosing when the circuit breaker “stealthly trips”.

02

protection start

In most cases, the protection action first issues a tripping command and then the reclosing command is required to issue a closing command. Therefore, the reclosing can be started by the protection.

When the protection device issues a single-phase trip command and checks that there is no current in the phase line, or when a three-phase trip occurs and there is no current in all three-phase lines, reclosing is started. This starting method is implemented by the protection itself through internal software. Reclosing cannot be started when the circuit breaker accidentally trips using the protective start-reclosing method .

How to set the automatic reclosing action time

The reclosing time is the time from when the main contacts of the circuit breaker are disconnected and there is no flow in the line to when the reclosing device sends out the closing pulse.

⑴

The three-phase reclosing method is usually used on single-sided power lines. The reclosing time should be the power outage time plus the margin time minus the inherent closing time of the circuit breaker.

Among them, the power outage time is the arc extinguishing time and the short-circuit point de-dissociation time, while the inherent closing time is the period from the circuit breaker receiving the closing pulse to the circuit breaker main contact closing. This time is carried out simultaneously with the fault point de-dissociation time. , needs to be removed when calculating the reclosing time.

⑵

The longitudinal protection on the double-sided power line will instantly remove the fault within the entire length of the line. If there is only distance and zero-sequence protection that reflects the electrical quantities on one side, the protection action time on the opposite side will likely be longer than on this side . Reclosing must take into account the delay on the opposite side.

At the same time, when single-phase reclosing and comprehensive reclosing are used for bilateral power lines, the impact of latent current must also be considered if single-phase tripping of the line occurs .

Extension: A single-phase ground fault occurs on the line. The relay protection only disconnects the faulted phase from both sides of the line through the phase selection component . The non-faulty phase still continues to operate. The non-faulty two-phase voltage passes through the inter-phase capacitance and the other two-phase current passes through the interphase. Mutual inductance provides short-circuit current to the short-circuit point, so that a certain amount of current still passes through the arc channel at the fault point. This current is called latent current.

Its size is related to the parameters of the line. The higher the line voltage, the longer the line, the greater the load current, and the greater the latent current.

Due to the influence of latent current, the single-phase reclosing time is generally longer than the three-phase reclosing time to facilitate arc extinguishing.

Submersible current diagram

6: What is the “acceleration” of reclosing?

If a permanent fault occurs in the line, the system will be impacted by the fault again after reclosing, which is extremely detrimental to the stable operation of the system. The “acceleration” of reclosing can effectively reduce the impact of reclosing and permanent faults on the system. . Reclosing acceleration is divided into front acceleration and rear acceleration:

01

Acceleration before reclosing

When a fault occurs on the line, the protection close to the power supply side first acts non-selectively and instantaneously to trip, and then relies on reclosing to correct this non-selective action. After reclosing the faulty line, its action time limit is based on the stepped time limit. According to the time limit of characteristic matching, front acceleration is generally used in radiation lines with several series connections, and the reclosing device is only installed on a section of the line close to the power supply.

Although the first trip is fast, it may be a non-selective trip, causing the power outage to expand. Therefore, this acceleration method is only used on direct distribution lines for unimportant users.

02

Acceleration after reclosing

When a line fault occurs, the protection selectively removes the fault, and the reclosing circuit restores power supply after a single reclosing operation. If the reclosing occurs due to a permanent fault, the protection device will trip the circuit breaker without time limit and without selective action. This method is called post-reclosing acceleration.

7: What is the principle of reclosing charging and discharging?

In analog protection , resistors and capacitors are used to realize charging and discharging. When the reclosing device sends a closing command, the voltage on the capacitor is used to discharge the outlet relay, thereby completing the closing process of the circuit breaker. Only when the charging time exceeds 15 seconds is the voltage on the capacitor sufficient to cause the relay to operate.

There is a counter in the reclosing program in microcomputer protection, which simulates the charging and discharging of the capacitor by continuously counting and clearing the counter.

8: What are the conditions for reclosing charging and discharging?

In order to ensure that the reclosing can be reclosed normally and only once, reclosing is only allowed after charging is completed. The protection device can only allow reclosing to charge if the following conditions are met at the same time.

1) The reclosing pressure plate is in the input state;

2) All three-phase trip relays are active, that is, the circuit breaker is in the closed position;

3) There is no circuit breaker low pressure latching reclosing and other external latching reclosing inputs;

4) When using comprehensive reclosing or three-phase reclosing, there is no signal input for line TV disconnection. Line TV is used when three-phase tripping is used to detect line voltagelessness or to detect synchronized reclosing .

When reclosing is not allowed under normal operation or short-circuit fault operation, the discharge should be carried out immediately, the counter should be cleared, and the reclosing should be blocked. There are many discharge conditions for reclosing, which will not be described here .

9. Inspection conditions for automatic reclosing

There is no synchronization problem with reclosing in power side protection on single-sided power lines .

the single-phase reclosing method or the comprehensive reclosing method is used on a double-sided power line, the systems on both sides are always connected through the two normally operating phases after the single-phase tripping. At this time, there is no need to consider synchronization issues.

After a three-phase trip occurs on both sides of the power line, the systems on both sides may not have any connection. Synchronization issues need to be considered when closing the reclosing. In this case, the inspection conditions for reclosing are as follows:

01

Check the line for no voltage and check the synchronized reclosing

Both sides of the line are equipped with check line voltage-free and synchronous reclosing respectively. After the line is short-circuited and three-phase trips, the three phases have no voltage. Check that the line has no voltage and the reclosing side reaches the closing condition first. After the three-phase reclosing action time Then the closing command is issued, and then the synchronous reclosing side of the line is checked to find that there is voltage in the line and busbar and the synchronous closing conditions are met and the closing command is issued within the three-phase reclosing action time.

The check synchronization function can be enabled on the non-voltage side of the line, and the reclosing command can also be issued after the circuit breaker “stealthly trips”; while the no-voltage check function on the synchronization side of the line cannot be enabled, otherwise both sides may be closed at the same time. The gate causes asynchronous closing.

02

Check if the line has a pressure-retaining mother but no pressure, if the line has no pressure the mother-in-law has pressure, if the line has no pressure the mother has no pressure.

These three reclosing inspection methods have been added to the microcomputer protection used on 110kV lines and small ground current system lines below 110kV to adapt to the needs of different operating modes, and these three methods can also be used in combination.

03

for current in adjacent lines

This reclosing check condition is used on double circuit lines. When a circuit in a double-circuit line is short-circuited and the three phases on both sides are tripped, just check that there is current in the other circuit, indicating that the systems on both sides are still connected through the other circuit , and the closing conditions are met.

10: What are the special requirements for reclosing under 3/2 wiring?

When the 3/2 wiring mode line protection issues a tripping command, two circuit breakers must be tripped. The order of coincidence of the two circuit breakers is to close the side circuit breaker first and then the breaker. If the side circuit breaker fails to reclose and closes on the faulty line, the protection will trip the side circuit breaker again, and the circuit breaker will no longer reclose and a three-trip command will be issued.

In this wiring method, reclosing and circuit breaker failure protection are implemented in separate circuit breaker protection devices.

If the circuit breaker is closed first and then closes due to a permanent fault, then the circuit breaker is protected and tripped. If the circuit breaker fails at this time, a trip command will be issued to the circuit breakers on both sides, causing the adjacent operating interval to lose power.

If the side circuit breaker is closed first , it coincides with the permanent fault, and then the side circuit breaker is tripped for protection. At this time, the side circuit breaker fails, and a trip command will be issued to the circuit breaker and all circuit breakers on the bus. The bus will be powered off but will not affect all operating intervals. Send power normally.

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