Dynamic behaviors and protection strategy of synchronous condenser integrated power system under non-full phase fault conditions

Abstract

When a synchronous condenser connected power network encounters a non-full phase fault, the amplitude of the stator current is severely suppressed by the magnetic field generated inside the synchronous condenser, in which the sensitivity of failure protection of circuit breakers are affected resulting in rejection of failure protection. In severe cases, it may endanger the secure and stable operation of the synchronous condenser and the related equipment. In this paper, dynamic behaviors of a synchronous condenser without/with de-excitation action under non-full phase faults are investigated with the following four contributions: 1) A mathematical model under non-full phase fault conditions is established. The theoretical value of fault currents is calculated when the synchronous condenser is without/with de-excitation action. 2) The inferiority/superiority without/with de-excitation action is analyzed. The tendency of dynamic behaviors of variables, including the phase current, negative-sequence, and zero-sequence currents, after de-excitation action, is obtained. A selection criterion of failure protection is proposed according to the dynamic behaviors of negative- and zero-sequence currents. 3) Based on the consistent characteristics of the theoretical calculation, simulations in PSCAD/EMTDC and recorded on-site data from WaveEx, the fact that the simulation model established in PSCAD/EMTDC can provide an effective verification platform for practical applications and data analysis of a synchronous condenser integrated power grid under non-full phase faults is justified. 4) An improved operational threshold of failure protection of circuit breakers is proposed. It can reduce the rejection operation probability of failure protection, which improves the protection sensitivity and enhances the security of the system operation. The simulation results justify the necessity and reliability of the criterion setting proposed for failure protection.