Abstract: Current domestic generator rotor one-point grounding protection devices are mostly based on principles of Wheatstone bridge, switch sampling (ping pong), square wave power injection and DC voltage injection, etc. Drawbacks like large operating dead zone, poor protective selection, low sensitivity and inability to display real time rotor insulation variation tendency exist in independently operating protecting device. To overcome these drawbacks, the configuration, application and setting calculation of the generator rotor grounding protection system of Tongzilin Hydropower Station are studied. The results show that an appropriately-selected configuration scheme of the generator rotor grounding protection system can effectively and promptly discover the decline tendency of the rotor insulation, sending warning signal, and confirm the warning and trip-out signals through the rotor grounding protection system based on two different principles.