Analysis on the negative sequence impedance directional protection for stator internal fault of turbo generator

In order to protect more turn-to-turn faults for the turbo-generator with only three lead-out terminals in the neutral side, this paper applies a new principle protection- negative sequence impedance directional protection of fault components for stator internal asymmetrical fault. By means of Multi-loop Method, all possible internal short-circuit faults and single branch shutdown faults of a 300MW turbo-generator are calculated to obtain the protection performance. Calculation and performance analysis show that, this new principle protection is superior to other existing protections in the aspect of sensitivity and protection range, especially for interturn faults of turbogenerator stator winding. In addition, it won´t incorrectly trip on external faults. Thus, this new principle protection can provide safeguard of high quality for internal faults in turbo-generator with only three lead-out terminals in the neutral side.