A new criterion for GCB open-phase protection in large pumped storage units

In the Guangzhou Pumped Storage Power Station A (GPSPSA), a single-phase disconnection fault of a generator circuit breaker (GCB) caused the preemptive action of a zero sequence overvoltage protection at the low voltage side of the main transformer which expanded the accident scope. To investigate this disconnection fault, a simulation model is built in the PSCAD environment and is verified by the dynamic simulation system of Nari-relays Company. Then the GCB single-phase disconnection fault in GPSPSA is also reproduced. Results of simulations and experimental studies reveal some fault features to help understanding this disconnection fault. Based on these results, a new criterion, using the phase angle difference of the zero sequence fundamental voltage between the generator terminal and the low voltage side of the main transformer is proposed for the GCB open-phase protection.