How is the overvoltage during the operation of vacuum circuit breaker generated? How can it be suppressed?
1. Causes of operating overvoltage
Cut-off overvoltage
When the vacuum circuit breaker cuts off the inductive load (such as motor, reactor), the current is forcibly cut off before zero point, resulting in the sudden release of electromagnetic energy on the inductive load, generating high-frequency oscillation overvoltage. This overvoltage has a high amplitude and a large wave steepness, which can easily damage the insulation of the equipment.
Multiple restrike overvoltage
After the cut-off overvoltage, if the contact is not completely extinguished, the arc may reignite, and the power supply charges the capacitor multiple times to form a resonant overvoltage. The amplitude of this overvoltage can reach 3-5 times the rated voltage, which is the main cause of damage to equipment such as motors.
Other types
Includes overvoltage caused by contact bounce (power frequency overvoltage) and capacitive load overvoltage when breaking capacitive load, but the former has less impact and the latter requires special treatment.
2. Suppression measures
A Limiting overvoltage amplitude
Lightning arrester: Installing lightning arresters in series can effectively limit the amplitude of cut-off overvoltage and restrike overvoltage, which is a common and economical method.
R-C absorber: Reduce the steepness of overvoltage wave (du/dt) through the resistor-capacitor circuit and reduce the insulation impact of the equipment.
B Optimize the operation mode
Synchronous closing: Use permanent magnetic operating mechanism to achieve synchronous closing to avoid overvoltage during no-load closing.
Reduce contact bounce: Improve the contact structure or increase the contact gap to reduce the overvoltage caused by bounce.
C Other technical means
Vacuum circuit breaker selection: Circuit breakers with strong arc extinguishing ability can reduce the risk of overvoltage, but they need to be selected in combination with load characteristics.
Cable design: Increase the cable cross-sectional area or use shielded cables to reduce the coupling effect of power frequency overvoltage.
The operating overvoltage of vacuum circuit breakers mainly comes from overvoltage and multiple restrike overvoltage. It is necessary to limit the amplitude through lightning arresters, R-C absorbers and other equipment, and optimize the operation mode and equipment selection to ensure the safe and stable operation of the power system.
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