1、 Air leakage of vacuum interrupter

1. Fault phenomenon and cause

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 6.5 × 10-1.3 × Within 10 PA. Different vacuum interrupters, different structures of dynamic and static contacts, different sealing of shielding cover, different shell materials, different bellows materials and processing methods will affect the performance of vacuum interrupters. China's vacuum technology can 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 vacuum circuit breaker is determined by the electrical life of vacuum interrupter. The selection of pollution level, humidity and salt spray in the application or storage environment of high-voltage vacuum circuit breaker is not appropriate, and harmful gas and condensation cause pitting corrosion of bellows, which can lead to air leakage of bellows, cover plate and sealing surface.

With the increase of service time and breaking times of vacuum interrupter, its vacuum degree can also gradually decrease, which will affect its breaking capacity and withstand voltage level to a certain extent. The contact of vacuum circuit breaker is mostly butt joint structure, which may produce rebound in varying degrees during opening and closing operation. Whether opening rebound or closing rebound will bring harm to operation. The impact speed and impact force during opening and closing are large, and bouncing may cause deformation of contacts and conductive rods, or even cracks. Bouncing may lead to forced vibration of bellows, cracks and air leakage of arc extinguishing chamber.

The vacuum circuit breaker breaks the current and extinguishes the arc in the vacuum bubble, but the vacuum circuit breaker itself has no device to qualitatively and quantitatively monitor the vacuum degree characteristics, so the vacuum degree reduction fault is a hidden fault, and its risk is far greater than that of the dominant fault. The decrease of vacuum degree will seriously affect the ability of breaking overcurrent of vacuum circuit breaker, and lead to a sharp decline in the service life of circuit breaker. In serious cases, it will cause switch explosion.

2. Fault prevention

The vacuum degree in the tube of the arc extinguishing chamber must be checked regularly during the use of the vacuum circuit breaker. At present, there are inspection methods:

① The vacuum arc extinguishing chamber with glass shell can be visually inspected regularly. Under normal conditions, the surface color of internal shielding cover and other components should be very bright, and light blue arc light will be emitted when breaking the current. When the true space drops seriously, the internal color will become gray, and a dark red arc will be emitted when the current is disconnected.

② Conduct a power frequency withstand voltage test (42 kV) regularly (about 3 years). When the dynamic and static contacts maintain the rated opening distance, if the power frequency withstand voltage is not lower than the rated power frequency withstand voltage, it indicates that the vacuum degree meets the use requirements. If continuous breakdown or glow discharge occurs in the vacuum interrupter during the pressure rise, it indicates that the vacuum degree of the vacuum interrupter has been seriously reduced and can no longer be used.

3. Fault handling

To ensure that the overtravel and contact stroke of high voltage vacuum circuit breaker are within the specified range, and to reasonably select the use and storage environment is an important measure to solve the problem of air leakage in vacuum interrupter.

During the installation or maintenance of the vacuum circuit breaker, in addition to strictly adjusting the overtravel of the measuring contact according to the requirements in the product installation manual. The contact surface of the vacuum interrupter will gradually be electrically worn after multiple breaking currents, and the contact stroke increases, which is equivalent to the increase of the working stroke of the bellows, and the service life of the bellows will decline rapidly. Generally, the maximum allowable contact electrical wear is about 3mm. When the cumulative wear value reaches or exceeds this value, the breaking performance and conductivity of the vacuum interrupter will decline, The service life of vacuum interrupter has reached.

4. In order to accurately control the electric wear value of the contact of each vacuum arc extinguishing chamber, the opening distance and overtravel must be accurately measured and compared during each preventive test or maintenance from the beginning of installation and use of the arc extinguishing chamber. The cumulative reduction value after contact wear is the cumulative electric wear value of the contact head

Before the new circuit breaker is put into operation, the opening and closing speed shall be measured, because it can not only establish the original technical data, but also find some problems in product quality in time, so as to take measures in time.

When the vacuum degree decreases, the vacuum bubble must be replaced or the vacuum circuit breaker must be replaced, and the travel, synchronization, bounce and other characteristic tests must be carried out.