Validity of Frequency Response Analysis (FRA) for Diagnosing Large Salient Poles of Synchronouos Machines

Frequency Response Analysis (FRA) is a technique under research for its application in rotary electrical machines. Even though FRA has been used for around 40 years in power transformers diagnosis, its application is still brand new in synchronous machines. The FRA technique is based on the comparison to a previous reference test that is done in healthy conditions. This article presents numerous experimental factory tests in a pole of a 40-MVA synchronous machine and onsite tests upon a 106-MVA synchronous generator in a hydro power plant where the FRA test was performed on a pole inside and outside the machine. Furthermore, simulations were executed in order to calculate the impact of the stator core on the FRA reference test. The main contribution of this article is demonstrating that the stator core has a significant influence on poles FRA results. Therefore, FRA tests done inside the machine cannot be compared to FRA tests performed outside the machine or vice versa, in order to avoid fault positives. FRA can be considered a suitable technique for the ground and interturn faults detection in poles of large synchronous machines.