What kind of vacuum circuit breaker is suitable for switching high-voltage capacitors?

What kind of vacuum circuit breaker is suitable for switching high-voltage capacitors?

Reactive power compensation in power systems is an effective means to increase system operating voltage, reduce network losses, and improve system stability.

Conventional loads (impedance) in the power system:

1) Resistance 2) Inductive reactance 3) Capacitive reactance
The generation of closing surge current: In order to improve the power factor during the operation of the power grid, capacitors are put into operation, and the closing surge current is generated at the moment of closing operation. Because at the moment of the first closing and operation of the capacitor, it is in an uncharged state, and the current flowing into the capacitor is only limited by its circuit impedance. Due to the close proximity of the circuit state to a short circuit at that time, the impedance of the circuit is very small, resulting in a significant surge current flowing into the capacitor.
The maximum value of surge occurs at the moment of closing. If, after the capacitor is cut off and out of operation, it is not fully discharged before closing again, the inrush current generated by closing is twice that of the closing inrush current when it is not charged. Because the capacitor is still in a charged state after being cut off, and the capacitor is put back into operation, it happens to be in the same system voltage and opposite charging voltage direction, so the closing surge current is relatively large.
Several Key Issues on Switching Capacitors

Heavy penetration

Reignition

NSDD (Non self-sustaining destructive discharge)
During the capacitive current switching test, reignition is allowed. According to the heavy breakdown performance of the circuit breaker, it can be divided into two levels:
C1 level: The capacitive current opening and closing test verified in specific type tests (6.111.9.2) has a low probability of heavy breakdown.
C2 level: The capacitive current opening and closing test verified by specific type tests (6.111.9.1) has a very low probability of heavy breakdown.
Improve the success rate of switching capacitor banks in vacuum circuit breakers
Improve the voltage resistance of vacuum arc extinguishing chambers
As the heart of vacuum circuit breakers, the vacuum arc extinguishing chamber plays an important role in the successful switching of capacitor banks. It is necessary for the arc extinguishing chamber manufacturer to study the structure and materials to ensure uniform electric field distribution, strong anti welding ability, and lower cut-off value.
2. Control the production process of the arc extinguishing chamber
During the processing of metal parts, try to avoid and remove burrs from clean parts, improve surface quality, and ensure surface smoothness;
Before assembly, perform ultrasonic cleaning on the components to remove particles inside the arc extinguishing system. Control the air humidity and suspended particles in the assembly room during the production process, reduce the storage time of contact components, timely assemble and seal, and reduce the probability of oxidation pollution.
3. Improve the design and assembly quality of circuit breakers, and control mechanical characteristics within a reasonable range
The conductive pole of the arc extinguishing chamber is well aligned to the neutral, arranged vertically, and not subjected to stress; The output power of the operating mechanism is appropriate, the opening and closing speed is within a reasonable range, and the opening rebound and closing rebound are minimized as much as possible; The quality control of circuit breaker parts and assembly is good.
4. Circuit breaker no-load operation and aging
After the circuit breaker assembly is completed, 300 no-load operations are required to stabilize the mechanical characteristics; Perform voltage and high current aging on the entire switch to eliminate burrs and reduce the reignition rate of the circuit breaker switching capacitor bank. Conducting parallel capacitor aging can quickly improve the product’s voltage resistance.
5. Improve the opening speed of circuit breakers
The time for the vacuum circuit breaker to withstand twice the Um voltage after opening is 13ms, and the circuit breaker must reach a safe opening distance before this. Therefore, the opening speed of the circuit breaker must meet this requirement, especially for the 40.5kV circuit breaker.
6. The Seasoned experiment
The effect of reducing the reignition of vacuum circuit breaker cutting capacitance is not significant by aging the high-voltage small current, low-voltage large current, and impulse voltage in the arc extinguishing chamber; The use of high-voltage and high current single-phase aging method has a certain effect on improving the performance of vacuum circuit breaker switching capacitor banks. The synthetic circuit test method is used to aging the vacuum circuit breaker switching capacitor banks.