1 GENERATOR FIELD WINDING SHORTED TURN DETECTION TECHNOLOGY

The use of air-gap magnetic flux probes has proven effective in the detection of generator rotor winding shorted turns and has helped to improve the quality of predictive maintenance decisions concerning when or if to perform rotor rework. Analysis of air-gap flux probe data can pinpoint the number and location (pole and coil) of shorted turns without having to take the generator offline. This paper will discuss the theory, methodology and benefits of detecting shorted turns in generator rotors. A number of case studies will be presented. EFFECTS OF SHORTED TURNS IN ROTOR WINDINGS The impact of operating a round rotor generator with rotor winding shorted turns depends upon many factors1. If the percentage of total turns shorted out is small, the generator may be able to run at rated load for years without further problems. However, larger shorted turn percentages can cause operating conditions that may limit unit loads. If the problems become severe, forced outages may occur. Conditions that may result in running a rotor with shorted-turns include: 1. Rotor unbalance that varies with field current changes (thermal sensitivity). Coils with shorted-turns operate at lower temperatures than coils without shorted-turns. This i