Identification and replacement of the vacuum level of the interrupter
1. Identification of the vacuum degree of the arc extinguishing chamber
The vacuum degree of the vacuum circuit breaker is directly related to the insulation performance and arc extinguishing performance of the circuit breaker, and it is difficult to correctly judge the vacuum degree of the arc extinguishing chamber in practical work, and the commonly used method is to use the power frequency withstand voltage method to qualitatively judge whether the vacuum degree is qualified or not.The fracture power frequency withstand voltage test is the most effective method to check the vacuum degree of the arc extinguishing chamber, and is currently widely used.
Pull the two contacts of the arc extinguishing chamber to the rated opening distance, and apply the rated power frequency withstand voltage between the contacts, if flashover occurs, it means that the vacuum degree has been reduced.
When the power frequency withstand voltage test is carried out, various forms of luminescence often occur in the vacuum arc extinguishing chamber. If flash point occurs, moving sparks, or a light cyan glow appears on the inner wall of the glass. These luminescence phenomena are normal luminescence phenomena unique to vacuum devices, and they are independent of the vacuum degree. Only when a glow is generated in the arc extinguishing chamber that fills the space inside the arc extinguishing chamber can it be judged that the vacuum level is poor. The color of this glow is related to the composition of the gas: such as air is purple red, hydrogen is orange, alcohol is white, moisture is white and slightly yellow and so on. If this glow is generated in the arc extinguishing chamber, flashover occurs within 1 minute of the rated power frequency withstand voltage, and the vacuum degree of the vacuum interrupter can be judged to be unqualified.
When there are no specific regulations, 42KV power frequency voltage is generally added to the vacuum circuit breaker of 10KV, and the withstand voltage is 1min. During the test, the voltage should be slowly raised from zero to 70% of the rated voltage, stable for 1min, and then evenly raised to the rated voltage of power frequency with 0.5min, if it can be maintained for 1min without tripping and current mutation of the test equipment, it is qualified.
Current setting of the test transformer:
For a single vacuum interrupter test, the high-voltage side current should be set at 20mA, such as a test of 2~6 arc extinguishing chambers when the high-voltage side current should be set at 40mA.When the power frequency withstand voltage is above 42KV, the vacuum device has X-ray radiation. Therefore, there should be radiation protection measures during the test, or a sufficient distance should be maintained between the tester and the test product. To prevent the harm of X-rays to the body.
2. Replacement of arc extinguishing chamber
When the vacuum interrupter is in one of the following situations, it should be replaced.
(1) The vacuum degree is significantly reduced or the power frequency withstand voltage test is unqualified.
(2) The mechanical life of the arc extinguishing chamber has reached the specified value.
(3) The wear of the dynamic and static contacts is greater than or equal to 3mm, and it has reached the specified value.
(4) The arc extinguishing chamber has been damaged and can no longer work normally.
The work of replacing the arc extinguishing chamber is relatively simple, generally can be carried out according to the procedures specified in the manufacturer's instruction manual, after the replacement, the assembly size of the equipment, the stroke of the circuit breaker, the overstroke, the opening distance should be measured, and the unqualified should be adjusted. Then the power frequency withstand voltage test is carried out.
3. Precautions for replacing the vacuum arc extinguishing chamber
(1) The arc extinguishing chamber must be replaced with the same type of arc extinguishing chamber, and other models of arc extinguishing chamber are not allowed to be replaced.
(2) When assembling, attention must be paid to the coaxiality of the conductive rod and the axis of the arc extinguishing chamber, and the coaxiality error is generally required to be not more than 2mm, so as to avoid the arc extinguishing chamber from being affected by shear and shear forces.
(3) When the circuit breaker is divided and closed, the bellows should not be resisted and should not be rubbed against any part.
(4) The trajectory of the moving conductive rod should be straight, and sparks should not be generated around the bellows at any time, and the compression and stretching amount of the bellows should not exceed the limit opening distance allowed by the contact.
(5) The pressure ring on the end face of the arc extinguishing chamber should be uniformly stressed in all directions.
(6) The guide sleeve can be made of polytetrafluoroethylene or high temperature resistant nylon. If a metal guide sleeve is used, the distance between the guide sleeve and the bellows should be controlled to avoid sparks between the bellows and the guide sleeve due to the voltage drop formed under strong current.
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