Protection configuration for the start-up testing of series transformer in UPFC

For the special start-up testing method and energizing path of series transformer in the UPFC, a temporary protection configuration method is proposed for the start-up testing. With energizing mode, the two-stage temporary overcurrent protection is setup to the valve-side breaker of shunt transformer to protect the series transformer as energizing, and the method for fault current calculation and protection setting is proposed based on the equivalent circuit of series transformer. What's more, a series transformer energizing function of UPFC protection is provided, which include: the differential protection is setup to the valve-side connecting lead between the shunt transformer and series transformer, and the inter-trip protection function is designed to isolate the series transformer and trip the power source under the condition of the series transformer weak fault. Finally, the simulations with fault on charged region are conducted, which is indicated that is can satisfy sensitivity and speed of protection. The protection configuration can be implemented in the field.