A Case Study on Protection of Pumped Storage Hydro-Generator Against Stator Earth Fault

Over the last few decades, the reliability of electrical grid on pumped storage hydro-electric generation has increased. The synchronous machines used in pumped storage scheme work as generator as well as motors as per the load demands. The protection of these machines is essential for continuous operation and consequently meeting the varying electricity demands. Stator earth fault is known to be one of the severe fault that can occur in the generator and it can cause unwanted breakdown of unit for unscheduled span of time. To take the unit back into the operation, the stator is needed to be re-insulated and withstand various tests. This paper analyzes a case study of protection of 13.8 k V, 150 MVA synchronous motor/generator against stator earth fault and tests to be followed after re-insulation of stator slots. The paper focuses on the sub-harmonic injection scheme which is employed to detect stator earth fault in given hydro-generator. The mathematical modeling and MATLAB simulation for the same is stated and simulation results are discussed.