A Stator Internal Short-Circuit Fault Protection Method for Turbo-Generator Based on Instantaneous Power Oscillation Ratio

For large turbo-generators, the longitudinal differential protection can only reflect the stator internal inter-phase short-circuit fault, and cannot reflect the inter-turn short-circuit fault. The protection methods for inter-turn short-circuit faults have the problem of low sensitivity, such as the longitudinal zero-sequence voltage protection and the negative sequence component-based protection. Therefore, a stator internal short-circuit fault protection method for turbo-generator based on instantaneous power oscillation ratio (IPOR) is proposed in this paper. The instantaneous power variation of the generator before and after the fault is analyzed, and the IPOR is calculated by using the balanced power component and the oscillatory power component. Then, the method to judge whether the generator has an internal short-circuit fault based on the amplitude and phase of IPOR is proposed. The experimental results verify the effectiveness of the proposed protection method, which has a high sensitivity to the inter-turn short-circuit faults with a small turn difference. The protection is stable and does not malfunction during the system oscillation. In addition, the action time of the protection method does not exceed 1.5 power frequency cycles under various working conditions, which can meet the speed requirements of generator protection.