Static excitation resistant rotor insulation for turbine generators

This paper summarizes the ongoing testing and developed operational parameters from Siemens Westinghouse Power Corporation evaluations of static excitation voltage applied to turbine generator rotor insulation. Testing and service performance of electric motor insulation shows electrical life is adversely affected when solid state drive systems are applied. Therefore, there is a concern about the electrical life of generator rotor insulation when driven by static excitation systems, especially with high ceiling excitation systems. The high ceiling static excitation systems for turbine generators produce an output voltage with a large AC or pulse component at a designed repetition rate of typically 360 Hz. Since rotor insulation has not typically been exposed to AC voltage, the AC electrical life of the rotor insulation was not a technical issue and little was known about its affects on service life. Since static excitation has become popular, a program was developed to investigate the AC electrical life of rotor insulation. This paper defines static excitation voltage applied to generator rotor insulation and discusses its effects on service life through laboratory testing. Critical rotor insulation materials, like the turn to turn insulation and the slot cell insulation, are discussed for both air-cooled and hydrogen-cooled rotor designs.