Analysis And Treatment Of Common Faults Of Sf6 Circuit Breaker Operating Mechanism
1. Working principle of sf6 circuit breaker operating mechanism
sf6 circuit breaker spring mechanism is named because its arc extinguishing medium and the insulating medium of the contact gap after arc extinguishing are both high vacuum; it has the advantages of small size, light weight, suitable for frequent operation, and arc extinguishing without maintenance, and is widely used in distribution networks. Vacuum circuit breaker technical standards Vacuum circuit breakers have been vigorously developed in my country in the past decade and are still in the ascendant. The products have developed from several varieties of ZN1~ZN5 in the past to more than dozens of models and varieties now, with a rated current of 5000A and a breaking current of 50kA, and have developed to a voltage of 35kV.
Vacuum circuit breakers are the main switching devices in power systems. The role of vacuum circuit breakers in power systems is: when the power system is operating normally, vacuum circuit breakers can cut off and connect the no-load and load currents of lines and various electrical equipment; when a fault occurs in the power system, vacuum circuit breakers and relay protection cooperate to quickly cut off the fault current to prevent the expansion of the scope of the accident.
2. Main components of vacuum circuit breaker
1. Bracket: The frame for installing the functional components of the circuit breaker.
2. Vacuum arc chamber: It is the arc extinguishing element of the vacuum circuit breaker.
3. Conductive circuit: The current channel formed by connecting the moving end and the static end of the arc extinguishing chamber.
4. Transmission mechanism: Realize the closing and opening operation of the arc extinguishing chamber.
5. Insulation support: The insulating support connects the functional components to meet the insulation requirements of the circuit breaker.
6. Operating mechanism: It is the power drive device of the vacuum circuit breaker. The basic requirements of the vacuum circuit breaker for the operating mechanism are as follows: a. There must be sufficient closing output power; ensure that the vacuum circuit breaker has the ability to close the short-circuit fault current.
b. The output characteristics of the mechanism should match the reaction force characteristics of the vacuum circuit breaker as much as possible.
c. The vacuum switch has sufficient dynamic stability.
d. It must ensure that it can open normally at 65%~12 opening voltage, and cannot open at 30% rated operating voltage.
e. The operating mechanism should have the function of free tripping.
f. It has electric or manual operation function.
III. Common fault analysis and handling experience of vacuum circuit breakers
1. The vacuum degree of vacuum bubble of vacuum circuit breaker is reduced
The vacuum circuit breaker interrupts the current and extinguishes the arc in the vacuum bubble. Since the vacuum circuit breaker itself does not have a device to qualitatively and quantitatively monitor the vacuum degree characteristics, the vacuum degree is reduced, the fault is not easy to be found, and its danger is far greater than other obvious faults. The main reasons for the reduction of vacuum degree are: there are problems with the material or manufacturing process of the corrugated tube in the vacuum bubble, and leakage points appear after multiple operations; there are problems with the material or manufacturing process of the vacuum bubble, and there are tiny leakage points in the vacuum bubble itself; when the split vacuum circuit breaker is operated, the distance of the operating connecting rod is relatively large, which directly affects the synchronization, bounce, overtravel and other characteristics of the vacuum circuit breaker, and the speed of vacuum degree reduction is accelerated. The reduction of vacuum degree will seriously affect the ability and service life of vacuum circuit breaker to break current. When the vacuum degree is relatively low, it will also cause the explosion of vacuum circuit breaker. Therefore, when performing regular maintenance of vacuum circuit breaker, it is necessary to use vacuum tester to conduct qualitative test of vacuum degree on vacuum bubble to ensure that vacuum bubble has a certain vacuum degree; when the vacuum degree is reduced, vacuum bubble must be replaced, and travel, synchronization, bounce and other characteristic tests must be done.
2. Closing failure of vacuum circuit breaker
There are four reasons for vacuum circuit breaker to refuse to close: fault on the line; improper operation; operation, closing power supply problem or electrical secondary circuit fault; mechanical failure of circuit breaker body transmission mechanism and operating mechanism. To deal with the failure of circuit breaker to close, it is necessary to be good at distinguishing the scope of fault. First, determine whether the circuit breaker is closed on the pre-fault line to cause tripping. It can be judged by whether there is a short-circuit current during the closing operation, whether the meter indication impact swings, whether the lighting suddenly dims, and whether the voltage meter indication suddenly drops. If it is determined that the line is faulty, isolate the fault area before throwing the circuit breaker. To determine whether it is improper operation, check whether the closing fuse is installed, whether the control switch is reset too quickly or not in place, and whether the transfer switch is in the correct position. Check whether the operation closing power supply voltage is too high or too low, check whether the operation closing fuse is blown or has poor contact, check whether the control switch and auxiliary contacts have poor contact, and whether the circuit is broken or wired incorrectly. Check whether the operating mechanism is stuck and whether the auxiliary contacts and mechanism are improperly adjusted. It is generally caused by the unqualified gap between the connecting parts of the operating mechanism, and new high-hardness qualified parts need to be checked and replaced.
3. Vacuum circuit breaker failure
According to the different causes of the fault, it can be divided into: remote remote control operation of the vacuum circuit breaker, but the vacuum circuit breaker cannot be disconnected. The reasons are: disconnection of the opening operation circuit; disconnection of the opening coil; reduction of the operating power supply voltage; short circuit of the opening coil, reduced opening capacity; deformation of the opening top rod, and jamming during opening. If the opening failure occurs during an accident, it will lead to the expansion of the accident. Therefore, if the operator finds that the opening and closing indicator light is not on, he should promptly check whether the opening and closing circuit is broken; the maintenance personnel should pay attention to measuring the resistance of the opening coil and check whether the opening top rod is deformed during power outage maintenance; if the material of the opening top rod is copper, it should be replaced with steel; low-voltage opening and closing tests must be carried out to ensure the reliable performance of the vacuum circuit breaker.
4. Failure of the closing energy storage circuit of the spring operating mechanism of the vacuum circuit breaker
The phenomena of the closing energy storage circuit failure of the spring operating mechanism include: the opening operation cannot be realized after closing; the energy storage motor does not stop running, etc. The main reasons are that the installation position of the travel switch is too high or too low, and whether the travel switch is damaged. If the closing energy storage is not in place, if an accident occurs in the line and the vacuum circuit breaker refuses to open, it will cause the accident to leapfrog and expand the scope of the accident; if the energy storage motor is damaged, the vacuum circuit breaker cannot be opened and closed. When the operator is operating the reversal, he should pay attention to the closing energy storage indicator light to judge the closing energy storage situation. If the above fault occurs, the position of the travel switch should be adjusted to accurately cut off the power of the motor or replace the damaged travel switch. After the maintenance work is completed, the maintenance personnel should perform two opening and closing operations on site to determine that the vacuum circuit breaker is in good condition.
5. The opening and closing of the vacuum circuit breaker are different in phase, and the bounce value is large
This fault is a hidden fault, and the relevant data can only be obtained through the measurement of the characteristic tester. The reasons for this fault are: the mechanical properties of the vacuum circuit breaker body are poor. After multiple operations, due to mechanical reasons, the phases are different and the bounce value is large; the split circuit breaker has a large distance between the operating rods, and when the opening force is transmitted to the contact, there is a deviation between the phases, resulting in different phases and large bounce values. If the phases are different or the bounce value is too large, it will seriously affect the breaking current capacity of the vacuum circuit breaker and affect the service life of the vacuum circuit breaker. Because there are many hidden faults in the split vacuum circuit breaker, an integrated vacuum circuit breaker should be used when replacing the vacuum circuit breaker; during regular maintenance work, the characteristic tester must be used to perform relevant characteristic tests to detect problems in time. Through the analysis of common faults of vacuum circuit breakers and the summary of treatment experience, we can better guide power plants to operate, maintain, and overhaul vacuum circuit breakers, and ensure the safe and reliable operation of vacuum circuit breakers.
6. Other faults
After the circuit breaker mechanism stores energy, the energy storage motor does not stop. At this time, the installation position of the travel switch should be adjusted so that the normally closed contact of the travel switch can be opened when the rocker arm is in a high position; the DC resistance of the circuit breaker increases. At this time, it is necessary to adjust the arc extinguishing chamber contact opening distance and overtravel; the circuit breaker closing bounce time increases. The initial pressure of the contact spring can be appropriately increased or the contact spring can be replaced; if the gap between the crank arm and the shaft pin exceeds 0.3mm, the crank arm and the shaft pin can be replaced; adjust the transmission mechanism, and use the characteristics of the mechanism having a small transmission ratio when the mechanism exceeds the dead point of the active arm in the closing position; adjust the mechanism in the direction close to the dead point to reduce the contact closing bounce; the CT surface of the circuit breaker intermediate box discharges to the bracket; the circuit breaker arc extinguishing chamber cannot be disconnected. It is usually caused by the decrease in the vacuum degree of the arc extinguishing chamber, the decrease in insulation in the arc extinguishing chamber, and the unqualified withstand voltage.
IV. Summary
As a new generation of advanced switchgear, vacuum circuit breakers are gradually being widely used. However, with the increase in their application, the defect rate and failure rate are inevitably increasing. At present, there are many kinds of vacuum circuit breaker failures. In addition to some common failures analyzed in this article, some new problems may still occur in daily use. In order to make the vacuum circuit breaker work reliably, the operating personnel should strengthen the inspection and daily maintenance and inspection, and report and solve the problems in time. Maintenance personnel should strictly implement electrical preventive tests, strictly follow the requirements of regulations, ensure the quality of maintenance, improve the health level of equipment, and avoid accidents.
