It is then necessary to verify that the selected capacitors and reactors are suitably sized to limit inrush currents to less than a predefined maximum magnitude, which, for example, is 100 times the rated current, according to IEC 60871-1.
One of the unwanted effects is the overheating of capacitor banks that are needed to maintain the power factor within the parameters required by the power authority, with a resulting, significant reduction in the average working life. The ideal solution is to insert block reactors in series with capacitor banks.
Inrush current reactors reduce the current surge to an acceptable value when switching capacitor stages, helping to reduce overheating of the equipment. They are connected in series with each capacitor stage and enable efficient protection of the capacitor units.
Taking into account that the 5th harmonic exceeds the limit, the reactance rate of 5 % should be used. The parallel capacitor reactance rate of a capacitor has great influence on switching inrush current, harmonic suppression, a capacitor’ effective capacity and the capacitor’s insulation requirements.
It can be seen that the voltage at the end of the capacitor increases with the increase of the reactance rate, and then the insulation requirements of the capacitor are also improved. The voltage of a capacitor which has the series reactor will be increased, and the amplitude of the increase is related to the percent of the series reactor.
An effective protection against the high level of harmonics that can be present in the network is usually by installing detuned reactors in series with the capacitor units. A detuned reactor will increase the impedance of the capacitor units to the harmonic currents and will also perform the function of a damping reactor.