Abstract: It is able to make fitting analysis of the relations between unloaded electromotive force and excitation current for large turbo-generators. The paper compares the actual excitation current with the theoretical excitation current gotten from fitting experiments to judge whether there is inter-turn short circuit of rotor winding or not. The paper, based on the SIS data of generators, to solve the problem of low accuracy of pure linear fitting model puts forward the model fitting method from the perspective of powerless power piecewise fitting.The fitting function obtained from this method is the function of two variables which are powerless power and unloaded electromotive force,increasing the accuracy of fitting model and improving the sensitivity and reliability of diagnosing rotor inter-turn short circuit fault. According to the engineering practice, the method successfully verifies the rotor inter-turn insulation fault of a 600 MW generator.

    Key words: rotor inter-turn short circuit; linear fitting; insulation fault; powerless power