Abstract: An oil leakage fault inside a hydrogencooled generator was analyzed. Some possible reasons of the leakage, such as the leakage of the inner oil retainer, the large amount of leakage of the sealing pad, the blockage of the pressure oil back tube in hydrogen side, the sand hole of the large end cover and others, were excluded. By the bulge test, it was determined finally that the reason of the inner oil leakage of the generator was the leakage of the corrugated tube of the differential pressure valve. After replacing the sealing gasket, the oil leakage fault was eliminated. 

Key words: generator, sealing oil, differential pressure valve, inner oil leakage, gasket