A close（namely trip） fault is occurred in case switching of shunt capacitor at 10 kV side of certain 220 kV substation. In this paper

the 10 kV double star type capacitor bank is taken as an example to calculate and analyze unbalance voltage and unbalance current protection of double Y-shaped wiring. It is shown by the result that the unbalance current is more sensitive to the internal fault of the capacitor unit than that of unbalance voltage protection

but with the increase of single-arm capacitance

the protection sensitivity is reduced. The transient operation of the capacitor bank is analyzed by the theoretical calculation of different protection modes and with the use of ATP-EMTP software

finding that the initial unbalance of the capacitor unit has great influence on the protection. Although the capacitance deviation is no more than 2%

yet the protection trip can also be caused under the combined action power asymmetry and inrush current at closing etc. The capacitance of the capacitor bank shall be kept as balance as possible during the actual operation.