The problems existing in the operation and maintenance of vacuum circuit breaker are analyzed. The treatment methods and preventive measures are put forward.

Keywords: maintenance fault prevention and treatment

1 working principle of circuit breaker

When the current in the vacuum crosses zero, the plasma quickly diffuses to extinguish the arc, thus cutting off the current. Vacuum interrupter is the main component of vacuum circuit breaker, and the life of switch depends on the wear of contact and the vacuum degree of interrupter, which is an important technical index of vacuum circuit breaker.

2 circuit breaker vacuum bubble vacuum reduction

2. 1 Cause analysis

2. 1. 1 There is something wrong with the material or manufacturing process of the vacuum bubble, and there is a slight leak in the vacuum bubble itself.

2. 1.2 There is something wrong with the material or manufacturing and assembly process of the bellows in the vacuum bubble. With the increase of service time and breaking times of vacuum interrupter, its vacuum degree gradually decreases, which will affect its breaking ability and withstand voltage level to some extent.

2. 1.3 split vacuum circuit breaker, such as vacuum circuit breaker with electromagnetic operating mechanism, in operation, the mechanical characteristics of the switch, such as synchronization, bounce and overtravel, are directly affected because of the relatively long transmission distance of the operating connecting rod, which accelerates the reduction of vacuum degree.

2.2 The reduction of fault hazard vacuum will seriously affect the ability of vacuum circuit breaker to break overcurrent, and lead to a sharp decline in the service life of circuit breaker.

2.3 treatment method ① When the circuit breaker is regularly overhauled, the vacuum degree of the vacuum bubble must be qualitatively tested with a vacuum tester to ensure that the vacuum bubble has a certain degree of vacuum (the vacuum degree should not be lower than 6.6× 10-2Pa, and the vacuum interrupter newly produced by the manufacturer should be lower than 7.5× 10-4Pa). ② When the vacuum degree drops, the vacuum bubble must be replaced, and the characteristics such as travel, synchronization and bounce should be tested. (3) Do a good job in the statistics of limit breaking current. In daily operation, the normal breaking operation and short circuit breaking of vacuum circuit breaker should be recorded. When the limit breaking current L reaches the limit value given by the manufacturer, the vacuum interrupter should be replaced.

1 = n 1Ir+n2Ik；

Where: n 1- normal disconnection times;

IR refers to the rated working current of the circuit breaker provided by the manufacturer;

N2- number of short circuit disconnections;

The maximum breaking current of ik-10kv bus.

2.4 Precautions ① At present, the models of vacuum circuit breakers are complex, with numerous manufacturers and scattered product quality. Some vacuum circuit breakers have no spare parts, which brings difficulties to maintenance and overhaul. Therefore, when selecting vacuum circuit breakers, mature products produced by manufacturers with good quality and good reputation should be selected. (2) Select a vacuum circuit breaker with integrated main body and operating mechanism. (3) Operators should regularly check the vacuum circuit breaker seriously and strictly, and pay attention to whether there is discharge outside the vacuum bubble of the circuit breaker; Especially for the vacuum bulb of the glass shell, it is necessary to visually judge the color of the inner surface and the color of the arc light when the power is cut off. When the inner surface color darkens or the arc color is dark red during power failure, the vacuum degree of the vacuum bubble is basically unqualified, so it should be replaced in time after power failure. (4) During power outage maintenance, the maintenance personnel must test the characteristics of the circuit breaker, such as synchronization, bounce, travel, overtravel and loop resistance, to ensure that the circuit breaker is in good working condition. ⑤ The easiest way to check whether the interrupter is qualified on site is to carry out a 42kV power frequency withstand voltage test on the interrupter.

3 vacuum circuit breaker break-brake fault

3. 1 fault phenomenon ① The remote control of the circuit breaker cannot break the brake; (2) On-site manual brake cannot be opened; (3) the external line or equipment fault relay protection action, but the circuit breaker can't disconnect.

3.2 Cause analysis ① Break-brake operation circuit is disconnected; ② Break-brake coil is damaged; (3) the working power supply voltage is reduced; (4) When the resistance of open-circuit coil increases, the open-circuit kinetic energy decreases; ⑤ When the brake is released, the ejector pin is deformed, and the ejector pin is stuck flexibly, which reduces the brake release force; ⑥ During brake opening, the brake opening ejector rod is severely deformed and stuck; All landowners break-brake ejector rod moves, but break-brake pressure plate cannot be opened reliably.

3.3 Fault Hazard Breaker Break-in Fault will lead to accident leapfrog and expand the scope of the accident.

3.4 Treatment method ① Check whether the break-brake circuit is disconnected; (2) Check whether the break-brake coil is broken; (3) Measure whether the resistance value of break-brake coil is qualified; ④ Check whether the break-brake ejector rod is deformed; ⑤ Check whether the working voltage is normal; ⑥ Change the copper brake ejector pin into steel to avoid the ejector pin deformation; ⑦ Adjust the length of the brake release ejector pin and iron core to ensure reliable action; ⑧ The brake coil fixing frame should be fastened to prevent the brake coil fixing frame from moving up and down when the iron core moves.

3.5 Precautions ① If the operator finds that the start-stop indicator light is not on. Check whether the opening and closing circuit is disconnected in time; (2) Maintenance personnel should pay attention to measuring the resistance of the brake coil and check whether the screws of the brake coil fixing frame are tightened when the power is cut off; ③ Check whether the break-brake ejector rod is deformed; (4) If the material of the brake release ejector pin is copper, it should be replaced with steel; ⑤ Low-voltage opening and closing test must be carried out to ensure the reliability of the circuit breaker.

4 spring operating mechanism closing energy storage circuit failure

4. 1 fault phenomenon ① After closing, it is impossible to realize the break-brake operation; ② The energy storage motor keeps running IE, even causing the motor coil to be damaged by over-arching. 4.2 Cause analysis ① The installation position of the travel switch is low, which leads to the failure of energy storage of the closing spring, and the contact of the travel switch has been switched, thus cutting off the power supply of the motor, and the energy storage of the spring is not enough for the opening operation; (2) The installation position of the travel switch is on the upper side, so that the contacts of the travel switch are not switched in time after the energy storage of the closing spring is completed, and the energy storage motor is still in working state; (3) The travel switch or its contact is damaged, and the energy storage motor cannot stop running.

4.3 Hidden Trouble In the case that the closing energy storage is not in place, the line has an accident, and the circuit breaker can't break the brake, which will lead to an accident leapfrog and expand the scope of the accident.

4.4 Treatment method ① Adjust the position of the travel switch to realize accurate power-off of the motor; (2) Pay attention to the action of the travel switch during maintenance. If the travel switch is damaged, it should be replaced in time.

4.5 Precautions Operators should observe the closing energy storage indicator light when closing to judge the closing energy storage situation; After the maintenance work, the maintenance personnel should carry out many on-site opening and closing operation tests to ensure that the circuit breaker is in good condition.

At 5 o'clock in different periods, the rebound value is large.

5. 1 Cause analysis ① The mechanical performance of the circuit breaker body is poor, and the bounce value in different periods is too large due to mechanical reasons after repeated operations; (2) Because of the long distance between the operating rods, there is a deviation between phases when the opening force is transmitted to the contact, which leads to a large bounce value in different periods; (3) The closing impact stiffness is too large, resulting in the axial rebound of the moving contact; (4) The moving contact rod is poorly guided and shakes too much; ⑤ The perpendicularity between the contact surface and the central axis is not good, which leads to lateral sliding during contact.

5.2 If the fault hazard occurs in different periods or the bounce is large, it will seriously affect the ability of vacuum circuit breaker to break the overcurrent, affect the life of the circuit breaker, and even lead to the explosion of the circuit breaker in serious cases.

5.3 Treatment method ① Under the premise of ensuring the stroke and overtravel, the data of synchronous and bounce tests are within the acceptable range by adjusting the length of the three-phase insulation pull rod; (2) improve the machining accuracy of accessories, make the insulating bracket and the shaft closely cooperate, and the commutator closely cooperate with the steel pin and the shaft to reduce idle clearance; ③ Strengthen the quality control of assembly process to improve the quality of assembly process. During the assembly of vacuum circuit breaker, pay attention to reasonable installation to avoid additional force on vacuum interrupter; (4) Adjust the position of the conduit, so that the motion track of the moving contact of the interrupter passes through the axis of the interrupter, and the moving contact of the vacuum interrupter can move freely without jamming; ⑤ Moderately increase the pre-pressure of the contact over-travel spring.

By taking the above measures, the closing bounce of vacuum circuit breaker can be effectively controlled. If it cannot be achieved through adjustment, the vacuum bubble in the data unqualified stage must be replaced and readjusted until the data is qualified.

5.4 Precautions Because there are many hidden dangers in the split vacuum circuit breaker, the integrated vacuum circuit breaker should be used when replacing the circuit breaker; During regular maintenance, a characteristic tester must be used to test related characteristics, and problems can be found and solved in time.

6 Operation, maintenance and overhaul test

It is necessary to strengthen the maintenance of 10kV vacuum circuit breaker, and the following aspects should be done well in the maintenance:

6. 1 In the maintenance test, it is necessary to test the resistance of the conductive circuit of the switch, the mechanical characteristics of the switch, the power frequency withstand voltage test between the fractures and the vacuum test, and the test data should meet the requirements of the manufacturer. Power frequency withstand voltage test and vacuum test between fractures are effective methods to check whether the vacuum tube leaks.

6.2 In the periodic inspection of protection, the circuit breaker should be tested for tripping and closing to check whether the circuit breaker can operate reliably when the switch fails.

6.3 Transmission parts such as circuit breaker mechanism and transmission shaft should be injected with certain lubricating oil, and fasteners should be tightened and confirmed to ensure flexible transmission of circuit breaker.

6.4 Conduct vacuum degree test. There are several methods to measure the vacuum degree of vacuum interrupter:

6.4. 1 observation method If the shell of the vacuum interrupter is glass, the vacuum degree can be judged according to the color change of the getter film coated with barium on the inner wall of the glass: when the vacuum degree is good, the getter film is in a mirror state; When the vacuum degree becomes worse, the getter film is milky white. This method of observing the vacuum degree with naked eyes is not accurate and can only be used as a reference.

6.4.2 The power frequency withstand voltage method is to put the vacuum circuit breaker in the off-state and process the frequency voltage between the contacts of the vacuum interrupter to determine the vacuum degree. If the vacuum interrupter can withstand the power frequency voltage above 10 second, it can be considered that the vacuum degree meets the requirements. If the current increases with the increase of voltage and exceeds 5A, the vacuum degree is considered unqualified. This method is simple and easy.

6.4.3 Magnetically controlled vacuum tester Magnetically controlled discharge method usually applies one or several high-voltage pulses between contacts, the pulse width is tens to hundreds of milliseconds, and synchronous pulse current is introduced into the magnetic field coil to generate a pulsed magnetic field synchronized with the high voltage to measure the vacuum degree.

When the vacuum degree does not meet the requirements and is close to or lower than the national standard of 6.6× 10-2Pa, the vacuum interrupter should be replaced in time. For the vacuum circuit breaker whose vacuum degree has been greatly reduced, but it is still within the acceptable range, the test period should be shortened appropriately, and the downward trend of vacuum degree should be judged by combining with the previous measurement to decide whether to continue to use the vacuum circuit breaker.

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