Analysis and Treatment of Common Faults of Vacuum Circuit Breaker
First, vacuum circuit breaker working principle
The vacuum circuit breaker is named after its arc extinguishing medium and the insulating medium of the contact gap after arc extinguishment are all high vacuum; it has the advantages of small size, light weight, being suitable for frequent operation and arc extinguishing without maintenance, in the distribution network. The application is more popular. The vacuum circuit breaker technical standard vacuum circuit breaker has been developing vigorously in China for the past ten years and has been in the ascendant. Products from the past ZN1 ~ ZN5 several varieties developed to now dozens of models, varieties, rated current up to 5000A, breaking current reached a good level of 50kA, and has developed a voltage up to 35kV level.
Vacuum circuit breakers are the main switching devices in power systems. The role of the vacuum circuit breaker in the power system is: when the power system is in normal operation, the vacuum circuit breaker can cut off and connect the idle plant and load current of the line and various electrical equipment; when the power system fails, the vacuum circuit breaker and The relay protection cooperates to quickly remove the fault current and prevent the accident from expanding.
Second, the main components of the vacuum circuit breaker
1. Bracket: The body of each functional component of the circuit breaker is installed.
2. Vacuum interrupter: It is the arc extinguishing element of the vacuum circuit breaker.
3. Conductive loop: The current path that connects the moving end and the static end of the arc extinguishing chamber.
4. Transmission mechanism: Realize the opening and closing operation of the arc extinguishing chamber.
5. Insulation support: Insulation supports will connect various functional components to meet the insulation requirements of the circuit breaker.
6. Actuator: It is the power drive of the vacuum circuit breaker. The basic requirements of the vacuum circuit breaker for the operating mechanism are as follows: a. Sufficient closing output work is required; ensure that the vacuum circuit breaker has the ability to close the short-circuit fault current.
b. The output characteristics of the mechanism should be matched with the reaction force characteristics of the vacuum circuit breaker as much as possible.
c. The vacuum switch has sufficient dynamic stability.
d. It must be ensured that the sub-gates can be normally opened under 65%~12 sub-gate voltages, but not under the 30% rated operating voltage.
e. The operating mechanism should have a free tripping function.
f. With electric or manual operation function.
Third, vacuum circuit breakers common fault analysis and processing experience
1. Vacuum circuit breaker vacuum bubble vacuum reduction
The vacuum circuit breaker breaks the current in the vacuum bubble and extinguishes the arc. Because the vacuum circuit breaker itself does not have a qualitative, quantitative monitoring of vacuum characteristics of the device, so the vacuum is reduced, the fault is not easy to be found, the degree of danger is far greater than other dominant failures. The main reasons for the lowering of the vacuum degree are: the material or manufacturing process of the inner tube of the vacuum bubble is problematic, and the leaking occurs after many operations; there is a problem with the material or manufacturing process of the vacuum bubble, and there is a tiny leak in the vacuum bubble; When the vacuum circuit breaker is in operation, the distance between the operating linkages is relatively large, which directly affects the characteristics of the vacuum circuit breaker such as the synchronous, bouncing, and over-travel, so that the degree of vacuum reduction is accelerated. Vacuum reduction will seriously affect the capacity and service life of the vacuum circuit breaker breaking current. When the vacuum level is relatively low, it will also cause the vacuum circuit breaker to explode. Therefore, vacuum breakers must be used when vacuum circuit breakers are regularly inspected. The vacuum bubble is used for qualitative test of the vacuum degree to ensure that the vacuum bubble has a certain degree of vacuum; when the degree of vacuum is reduced, the vacuum bubble must be replaced, and the characteristics of the stroke, the same period, and the bouncing are tested.
2. Vacuum circuit breaker fails to close
There are four reasons why vacuum circuit breakers do not close: there are faults on the line; improper operation; problems with the operation, closing of the power supply, or failure of the electrical secondary circuit; mechanical failures of the transmission mechanism and the operating mechanism of the circuit breaker body. Dealing with the circuit breaker refused to close the fault, must be good at distinguishing the fault range. First determine whether the circuit breaker is integrated with the pre-faulted fault line to cause tripping. Can the meter indicate the impact swing and whether the lamp is caused by the short-circuit current from the closing operation? Suddenly darkened, the voltmeter indicates a sudden drop to judge. If it is found that the line is faulty, isolate the fault area and then cast the circuit breaker. To determine whether it is improper operation, check whether there is no closing insurance, whether the control switch is reset too quickly or not, and whether the switch is in the correct position. Check whether the 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 the auxiliary contact are in poor contact and whether the circuit is broken or incorrectly connected. Check whether the operating mechanism is stuck and whether the auxiliary contacts and mechanisms are adjusted improperly. Generally, it is caused by the gap of the connection parts of the operating mechanism being unqualified. It is necessary to inspect and replace the new high hardness qualified parts.
3. Failure of vacuum circuit breaker opening
According to the different causes of the fault, it can be divided into: remote control of the vacuum circuit breaker for remote operation; but the vacuum circuit breaker cannot be disconnected. The reasons are as follows: breakage of the opening operation circuit; disconnection of the opening coil; reduction of the operating power supply voltage; short-circuiting of the sub-gate coil, reduction of the sub-gate opening capacity; deformation of the stem of the sub-gate, and jamming at the sub-gate opening. If the failure of the opening occurs in an accident, it will lead to an increase in the accident. Therefore, if the operator finds that the sub-switching indicator is off, it is necessary to check whether the disconnecting and closing circuit is broken. The maintenance personnel should pay attention to measuring the resistance of the sub-opening coil and check whether the sub-gate is deformed. The material of the top rod is copper and it should be replaced with steel; low voltage switching and closing tests must be carried out to ensure the reliability of the vacuum circuit breaker.
4. Vacuum circuit breaker spring operating mechanism closing energy storage circuit fault
The phenomenon that the spring operating mechanism closes the fault of the energy storage circuit includes: after the closing operation, the opening operation cannot be realized; the operation of the energy storage motor does not stop. The reason for this is mainly whether the position of the travel switch is over or under and the travel switch is damaged. In the event that the closing energy storage is not in place, if a circuit accident occurs and the vacuum circuit breaker refuses to open and close the gate, it will cause the accident to go beyond the level and expand the scope of the accident. If the energy storage motor is damaged, the vacuum circuit breaker cannot be switched on and off. Operation personnel should pay attention to the closing energy storage indicator to judge the closing energy storage condition during the switching operation. If the above fault occurs, the position of the travel switch should be adjusted to achieve accurate power-off of the motor or replacement of the damaged travel switch. After the overhaul work is over, the maintenance personnel shall perform two sub-closure operations on the site to determine that the vacuum circuit breaker is in good condition.
5. The vacuum breaker has different values ​​during the different phases of closing and closing.
This fault is a recessive fault and must be measured by a characteristic tester to obtain relevant data. The reasons for this failure include: poor mechanical performance of the vacuum circuit breaker, multiple operations, due to mechanical reasons lead to different periods, the bouncing value is too large; split circuit breaker due to a large distance between the operating lever When the contact is made, there is a deviation between the phases, which results in a large number of different phases and bouncing. If the value is too large in different periods or bouncing, it will seriously affect the capacity of the vacuum circuit breaker breaking current, affecting the life of the vacuum circuit breaker. Because there are many hidden troubles in the split vacuum circuit breakers, one-piece vacuum circuit breakers should be used when replacing the vacuum circuit breakers; the characteristic tester must be used to conduct the relevant characteristic tests and the problems should be found in a timely manner. Through the common failure analysis and processing experience of the vacuum circuit breaker, it can better guide the power plant to do a good job of vacuum circuit breaker operation, maintenance, overhaul, etc., to ensure the safe and reliable operation of the vacuum circuit breaker.
6. Other faults
After the energy storage mechanism of the circuit breaker mechanism is stored, the energy storage motor will not stop. At this time, the installation position of the limit switch shall be adjusted so that the normally closed contact of the limit switch can be opened when the rocker arm is at the highest position; the DC resistance of the circuit breaker increases. At this time, it is necessary to adjust the opening distance and the over-stroke of the arc extinguishing chamber contact; the time for the closing and bounce of the circuit breaker increases. The initial pressure of the contact spring may be appropriately increased or the contact spring may be replaced. If the clearance between the arm and the shaft pin exceeds 0.3 mm, the arm and the shaft pin may be replaced; the transmission mechanism may be adjusted to utilize the mechanism to exceed the dead point of the active arm at the closing position. When the gear ratio is very small; adjust the direction of the mechanism to the near dead point, can reduce the contact closing bounce; breaker the middle box CT surface of the stent discharge; circuit breaker interrupter can not be disconnected. It is usually caused by the lowering of the vacuum in the arc extinguishing chamber, the lowering of insulation in the arc extinguishing chamber, and the failure of the withstand voltage.
Fourth, summary
Vacuum circuit breakers are widely used as a new generation of advanced switching devices. However, as their applications increase, it is inevitable that the defect rate and failure rate will increase. At present, there are many kinds of vacuum circuit breaker faults. In addition to the analysis of some common faults in this paper, some new problems may still occur in daily use. To make the vacuum circuit breaker work reliably, the operating personnel should strengthen inspections to intensify daily maintenance tests and timely find problems. Report on the solution. Maintenance personnel should strictly implement electrical preventive tests, strictly follow the requirements of regulations, ensure the quality of maintenance, improve the health of the equipment, and avoid accidents.
references
[1] Electrical Safety Work Regulations. (Power Plants and Electrical Substations) National Industry Standards.
[2] Guo Zhongli, high voltage electrician practical technology mechanical craft press
[3] Liu Yufu, Failure Analysis and Elimination of High Voltage Vacuum Circuit Breaker [J], Electrical Engineering, 2012(3)
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