Refurbishment of turbo alternator rotors and excitation systems in ageing power stations

Alternator winding faults are of two types, stator winding faults and rotor winding faults. Rotors and excitation systems begin to show signs of ageing after 20 to 30 years and rotor faults occur rather more frequently than stator faults during the lifetime of a machine. The author describes the experience of CESC Limited, the public utility which supplies electricity to the city of Calcutta, in connection with the protection of rotors, the location and repair of rotor earth faults, the problems which arise and the safeguards which have to be adopted when running a turbo alternator with a repeatedly repaired, and consequently weak rotor. The methods available for the refurbishment of ageing excitation systems using DC machines are also described