Improvement in Inter-Turn Faults Detection in Poles of Synchronous Machines by FRA Grounding Connection

Inter-turn faults are among the most common failures in electrical machines. While Frequency Response Analysis, (FRA) has been extensively used for power transformers diagnosis for the last 40 years. In this conventional, accurate and non-destructive technique for power transformer diagnosis, it is a usual practice to connect the chassis of the FRA test device to the transformer housing, normally grounded. The same practice has been applied for pole diagnosis, although no procedure has yet been established as standard since pole diagnosis using FRA is still an experimental technique. Nevertheless, this paper shows a different approach to diagnose inter-turns faults in poles by isolating the FRA chassis from the iron core. In this way, the capacity to ground has less influence, increasing FRA test sensitivity for inter-turn fault diagnosis. The method has been verified by experimental results in several spare poles belonging to 106 MVA and 40 MVA synchronous hydro-generators and also by two simulation models with both types of connections, grounded and FRA-isolated, achieving positive results.