How to solve the overvoltage problem that may be generated when vacuum circuit breakers interrupt high-frequency current?

When vacuum circuit breakers interrupt high-frequency current (such as interrupting unloaded transformers, motor starting current, etc.), the current is forced to be cut off (cut off) before it passes zero, resulting in significant operating overvoltage, which poses a threat to the protected equipment and system insulation. The key to solving this problem is to suppress the cut-off overvoltage and the high-frequency oscillation of the LC circuit caused by it.

The main measure is to install an overvoltage absorption device. The most common and cost-effective one is to connect a resistor-capacitor (RC) absorber in parallel between the load side of the vacuum circuit breaker and the protected equipment. The RC absorber uses capacitors to slow down the voltage mutation rate (i.e., reduce du/dt), while the resistor consumes high-frequency oscillation energy, thereby effectively damping the oscillation and reducing the overvoltage amplitude. The correct selection of the resistor-capacitor parameters is crucial, and they need to be accurately calculated and adapted according to the system voltage level, load characteristics, and expected high-frequency current characteristics to ensure that they can quickly absorb energy when overvoltage occurs.

Another important method is to install a zinc oxide arrester (MOA), which uses nonlinear resistance characteristics to quickly conduct and discharge energy when the overvoltage exceeds the threshold, providing reliable overvoltage limiting protection. The use of RC absorbers and MOA can complement each other and provide more comprehensive protection effects. RC is responsible for suppressing the voltage rise rate and oscillation, while MOA is responsible for clamping the overvoltage peak. In addition, source control should not be ignored. Selecting high-quality vacuum circuit breakers with lower interception levels and contact materials with better interception overvoltage characteristics (such as copper-chromium alloy) can essentially reduce the generation of interception overvoltage.

In actual engineering applications, a comprehensive evaluation is required in combination with specific load properties, system parameters and economic efficiency. RC absorbers and MOA are usually preferred or combined. After installation, strict testing and verification must be carried out to confirm that the overvoltage generated by the vacuum circuit breaker under high-frequency current interruption conditions can be effectively suppressed below the insulation tolerance level of the equipment to ensure the safe and stable operation of the entire power system. This is the key protection link that must be paid attention to when selecting and applying vacuum circuit breakers.