Rotor monitoring and protection for large generators

Structured development of field insulation systems for the rotors of large generators, including thermal ageing and life testing under laboratory conditions, followed by rigorous manufacture and testing is an requirement for service integrity. Accordingly a rotor telemetry system was initially developed which enabled a true measure of fault resistance (from 50000 to 500 ohm) to be made whilst running, accelerating, decelerating or also at standstill. This latter is very important if the machine has been idle for extended periods and subjected to moisture and contamination. The acceleration and deceleration measurement capability is useful for investigations of intermittent earth faults, which may change with varying centrifugal force. The system consists of three major components: a rotating module mounted on the main rotor shaft, an inductively-coupled stator unit which transfers power to the rotating module and also receives the transmitted signal, and finally a rack-mounted signal conditioning unit. The low-frequency AC injection and suitable filtering techniques eliminate supply-frequency effects and also enables DC field effects to be excluded. The machine-mounted components are encapsulated and the system has been certified for use with machines operating in potentially-hazardous atmospheres.