Air leakage problem of vacuum interrupter

1. Fault phenomenon and cause

The vacuum circuit breaker is characterized by arc extinguishing in vacuum, but it is not possible under any vacuum degree, but has good insulation and arc extinguishing performance within a certain vacuum degree range. The internal vacuum in the vacuum switch is usually in the range of 6.5×10-1.3×10 Pa. Different vacuum interrupters, different structures of dynamic and static contacts, different sealing of shields, different shell materials, different bellows materials and processing methods, etc., will affect the performance of vacuum interrupters. my country's vacuum technology has been able to ensure the vacuum degree required by the vacuum switch, and the sealing technology can ensure no air leakage and maintain the vacuum degree. The electrical life of the vacuum circuit breaker is determined by the electrical life of the vacuum interrupter. The pollution level, humidity and salt spray of the application or storage environment of the high-voltage vacuum circuit breaker are not suitable. Harmful gases and condensation will cause pitting corrosion of the bellows, which may lead to leakage of the bellows, cover plates and sealing surfaces. As the use time of the vacuum interrupter increases and the number of interruptions increases, its vacuum degree can also gradually decrease, and it will affect its breaking capacity and withstand voltage level to a certain extent. The contacts of vacuum circuit breakers are mostly butt-type structures, and different degrees of rebound may occur during the opening and closing operations. Whether the opening rebound or the closing rebound will cause harm to the operation. The impact speed and impact force during opening and closing are relatively large, and the bounce may cause deformation of the contacts and conductive rods, and even cracks. The rebound may cause the bellows to undergo forced vibrations that may crack and allow the arc chute to leak. The vacuum circuit breaker breaks the current and extinguishes the arc in the vacuum bubble, and the vacuum circuit breaker itself does not have a device for qualitatively and quantitatively monitoring the vacuum degree characteristics, so the vacuum degree reduction fault is a recessive fault, and its danger is far greater than the dominant fault. . The reduction of vacuum degree will seriously affect the ability of the vacuum circuit breaker to interrupt the overcurrent, and cause the service life of the circuit breaker to decrease sharply, which will cause the switch to explode in severe cases.

2. Troubleshooting

Ensuring that the high-voltage vacuum circuit breaker exceeds the stroke and the contact stroke within the specified range, and reasonably chooses the use and storage environment, is an important measure to solve the air leakage problem of the vacuum interrupter. During installation or maintenance of the vacuum circuit breaker, in addition to strictly following the requirements in the product installation manual, the measuring contact overtravel should be adjusted. The contact surface of the vacuum interrupter will be gradually electrically worn after breaking the current for many times, and the contact stroke will increase, which is equivalent to the increase of the working stroke of the bellows, and the life of the bellows will decrease rapidly. The maximum value of contact electrical wear is about 3mm. When the accumulated wear value reaches or exceeds this value, the breaking performance and conductivity of the vacuum interrupter will decrease, and the service life of the vacuum interrupter has expired.

In order to be able to control the electrical wear value of the contacts of each vacuum interrupter more accurately, it is necessary to measure the distance and over-travel accurately and carry out every preventive test or maintenance from the time of installation and use of the interrupter. By comparison, the accumulated reduction value after the contact wears out is the accumulated electrical wear value of the contact. The opening and closing speed of the new circuit breaker should be measured before it is put into operation, because it can not only establish the original technical data, but also find some problems in product quality in time, so as to take timely measures. When the vacuum degree decreases, the vacuum bubble or the vacuum circuit breaker must be replaced, and the characteristics tests such as stroke, synchronization and bounce must be done.