Developments in detecting interturn shorts in generator rotors using the RSO technique

This technique, the Recurrent Surge Oscillograph (RSO), involves applying a fast fronted step voltage to a winding and examining the terminal voltage waveform for reflections from shorted turns. An advantage for the manufacturer is that the test is quick and can be applied at different stages of coil winding to check integrity. However, the technique is very sensitive; it can detect turn to turn `shorts´ with resistances up to approximately 10 ohms. This has created an analytical problem because a satisfactory understanding of the mechanisms by which any reflections can occur has not yet been achieved. Minor trace differences may be indicative of high resistance `shorts´ or may be `spurious´. An investigation has therefore been started into the causes of such minor trace differences and this has led to the realisation that the indications observed can only be understood using multi-conductor transmission line theory. Examples are given of typical wave traces obtained from rotors with shorted turns and some giving spurious indications. Wave propagation is being studied theoretically and experimentally to develop a method of predicting waveshapes