A large steam turbine generator unit had repeated normal events and shutdowns following a history of disturbances, repair conditions, and balance conditions starting in 2019 until 2025. The most critical symptoms observed was an instantaneous overcurrent (IOC) trip in the excitation system, which occurred despite replacement of key control components. IOC trips were triggered instantly when the excitation supply was provided by an AC supply and 3-4 minutes after trip when used with battery supply. The trips corresponded to an approximately 25 Amp DC field current, which was 2.5 times the rated shunt reference of 10 Amps.
MotorDoc® LLC was contacted to evaluate the condition of the generator knowing that there would be limited run time and limited repair history was provided. The generator was to be partially disassembled for inspection and offline testing including: ALL-TEST Pro 7 Motor Circuit Analyzer (ATPro7), Electrom 12kV HO surge tester with low voltage and PD testing, and the EMPATH electrical signature analyzer (EMPATH) for a run test following reassembly.
Contact us for field testing or for more information on EMPATH ESA or ALL-TEST Pro technologies. info@motordoc.com
