(1) Function of series capacitor

1) Increase the voltage at the end of the line. The capacitor connected in series in the line uses its capacitive reactance XC to compensate the inductive reactance XL of the line, so as to reduce the voltage drop of the line, so as to improve the voltage at the end of the line (receiving end). Generally, the maximum voltage at the end of the line can be increased by 10% ~ 20%.

2) Reduce the voltage fluctuation at the receiving end. Series capacitor can eliminate the violent fluctuation of voltage when there is a great variety of impulse load (such as electric arc furnace, electric welding machine, electric rail, etc.) at the receiving end of line. This is because the compensation effect of series capacitor on voltage drop in the line changes with the load passing through the capacitor. It has the performance of instantaneous regulation with the load change and can automatically maintain the voltage value at the load end (receiving end).

3) Improve the transmission capacity of transmission lines. Because the compensation reactance XC of capacitor is connected in series, the voltage drop and power loss of the line are reduced, and the transmission capacity of the line is increased accordingly.

4) The power flow distribution is improved. Some capacitors are connected in series on some lines in the closed network, which partially changes the line reactance and makes the current flow according to the specified line, so as to achieve the purpose of economic power distribution.

5) Improve the stability of the system. After the line is connected in series with capacitors, the transmission capacity of the line is improved, which itself improves the static stability of the system. When the line fault is partially removed (for example, the double circuit is removed once, but the single-phase grounding of the circuit is removed one phase), the equivalent reactance of the system increases sharply. At this time, the series capacitor is forced to compensate, that is, the number of series and parallel capacitors is forced to change in a short time, and the capacitance XC is temporarily increased, so that the total equivalent reactance of the system is reduced, and the ultimate power (Pmax = u1u2 / XL XC) is increased, so as to reduce the total equivalent reactance of the system Improve the dynamic stability of the system.

(2) Function of shunt capacitor

Parallel capacitors are parallel connected to the bus bar of the system, which is similar to a capacitive load on the bus bar of the system. It absorbs the capacitive reactive power of the system, which is equivalent to the shunt capacitors sending inductive reactive power to the system. Therefore, shunt capacitor can provide inductive reactive power to the system, improve the power factor of the system operation, and improve the voltage level of the bus at the receiving end. At the same time, it reduces the transmission of inductive reactive power on the line, reduces the voltage and power loss, so as to improve the transmission capacity of the line.