SC A1 ROTATING ELECTRICAL MACHINES PS2 LIFE MANAGEMENT OF GENERATORS Refurbishment, Replacement, Power up-rating and Improvements TREND FOR STATIC EXCITATION SYSTEMS IN LARGE THERMAL GENERATORS D. K.CHATURVEDI NTPC LIMITED, INDIA dkchaturvedi@ntpc.co.in Background This paper summarizes problems with the reliability of brushless excitation system based on operating experience in Indian power plants Its focus is on the huge Generation loss to address any repair on exciter rotor. Dependency of user on OEM for arranging spares during emergency. TG deck extension cost is more than complete excitation system cost. Performance advantages of Static Excitation System Absence of rotating exciter - High Initial response Improved performance during transients & load throw-offs Great impact of PSS to the transient stability Elimination of rotating parts -reduced operating cost High reliability & availability Hardware with Power Electronic can be subjected to high mechanical stress BRUSHLESS NEEDS LONG TG DECK SC A1 2014 SESSION   Attribute Static excitation system Brushless excitation system Remarks 01 Response Very fast acting - Response Ratio 3-5 Slower response Response Ratio ~2 Critical for System Stability 02 Components on rotor Very few large number of components on rotor: diodes, fuses, flexible CONNECTION, PMG, exciter component failures in Brushless causes long outages 03 TG Deck SMALL LONG deck cost is higher in Brushless 04 Transfer of current through brushes brush-gear slip-ring assembly No such requirement Available brush-gear are now reliable 05 Machine rating large Generators and Hydro generators Generally for small Generators brushless is not recommended for remote hydro Generators 06 Energy Saving Lower losses Higher Losses Estimated difference 230kW for a 500MW machine 07 Field discharge Fast slow As Exciter is Involved Fault is fed for longer time in BLE. 08 Outage & Failure experience Very few failures Large number of failures Equipment down time is very high in BLE BRUSHLESS EXCITER FAILURES BRUSHLESS EXCITER ROTOR