Shaft voltages in generators with static excitation systems-problems and solution

Details on four types of shaft voltages are given, with emphasis on the occurrence, transmission and damaging mechanisms of shaft voltages from static excitation systems. A model for numerical simulation is presented and simulation results are compared with tests performed on a statically excited 1200 MVA turboset. A program of countermeasures is proposed, mainly including a type of passive RC-circuit connected through a grounding brush on the exciter end of the generator. This set of counter measures has successfully been tested on two turbosets, one of 190 MVA and one of 1200 MVA, showing the following advantages: reduction of shaft voltages to a harmless level; good access (even in nuclear power plants), low maintenance costs and long brush life; operation with or without grounding brush on the turbine end of the generator is possible; and easy monitoring is an additional feature