This primary of these protection transformer are connected to the star point of bank. In case any failure happens, there will be unbalance at secondary side of transformer generating unbalance voltage or current. Thus voltage or current relay will give instant command to tripping relay of controlling switchgear.

Series Reactor rating 0.2%, 1% or 6% of capacitor bank is designed & connected in series. This provides additional reactance in the circuit in order to limit inrush short circuit current to a safe value for purpose of protecting capacitor bank. 0.2% series reactors are neutral side while 6% are connected in line before capacitor bank.