A New Phase Sequence Exchanging Control Method for Reducing Impulse Current and Voltage

Phase sequence exchanging technology (PSET) is a recently developed emergency control technology for out-of-step power systems. The PSET system does not satisfy the condition of synchronization however, and will produce impulse current and impact torque. In this paper, the impulse current and impact torque produced by PSET are calculated. Taking the three-phase short circuit at the generator outlet as a reference, the impulse current generated by PSET is determined to be less than half of the three-phase short circuit at the generator outlet, which is within the system's endurable range. When the system connection reactance is 0.543 times larger than generator direct axis sub-transient reactance, it can endure the impact torque produced by PSET. To reduce the impact and improve the practicability of PSET, a split-phase switching control method is proposed in this paper. The characteristics of fast breaking are utilized to turn off the solid-state circuit breaker separately when the three-phase current is at zero-crossing, and after exchanging the phase sequence, it is turned-on separately when two sides of the three-phase voltage are equal. An example is provided to verify that the impact of PSET can be dramatically reduced by using the proposed control method instead of the traditional simultaneous switching control method.