Common Failure Causes And Treatment Measures For Low Voltage Pole-mounted Circuit Breakers
1.Lv Pole Mounted Circuit Breakers Vacuum bubble vacuum degree reduction
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 and the fault is not easy to be discovered, and its degree of 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 accelerates the speed of vacuum degree reduction.
The reduction of vacuum degree will seriously affect the ability of vacuum circuit breaker to break current and its service life. 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 the vacuum bubble has a certain vacuum degree; when the vacuum degree is reduced, the vacuum bubble must be replaced, and the travel, synchronization, bounce and other characteristic tests must be done.
Common faults of vacuum circuit breaker
2. Closing failure of vacuum circuit breaker
There are four reasons why vacuum circuit breaker refuses 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 and 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 swing is caused by the short-circuit current, whether the lighting suddenly dims, and whether the voltage meter indication suddenly drops. If it is determined that the line is faulty, isolate the faulty 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, whether the circuit is broken or the wiring is wrong.
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 to open
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, etc.
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 check whether the opening and closing circuit is broken in time; 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. [Common causes and treatment measures of vacuum circuit breakers]
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 achieve opening and closing.
When the operator is operating the switch, 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 achieve accurate power off 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 vacuum circuit breaker is opened and closed at different times, 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 too large; the split circuit breaker has a large operating rod distance, 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 current breaking capacity of the vacuum circuit breaker and affect the service life of the vacuum circuit breaker.
Since there are many hidden faults in split vacuum circuit breakers, integrated vacuum circuit breakers should be used when replacing vacuum circuit breakers; during regular maintenance work, characteristic testers must be used to perform relevant characteristic tests to detect problems in a timely manner. Through the analysis of common faults of vacuum circuit breakers and the summary of treatment experience, power plants can be better guided to operate, maintain, and overhaul vacuum circuit breakers to 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 the highest 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 characteristic that the transmission ratio is very small when the mechanism exceeds the dead point of the active arm in the closing position; adjust the mechanism towards the dead point to reduce the contact closing bounce; the surface of the CT of the circuit breaker middle box discharges to the bracket; the circuit breaker arc extinguishing chamber cannot be disconnected.
It is usually caused by the decrease of the vacuum degree of the arc extinguishing chamber, the decrease of the insulation in the arc extinguishing chamber, and the failure of the withstand voltage.
