Planned maintenance of high voltage rotating machine insulation based upon information derived from on-line discharge measurements

The drive to obtain improvements in plant economy, availability and useful operating life has led to an increasing interest in the possibility of monitoring all aspects of machine condition whilst the plant is operating in normal service. On-line monitoring of discharge activity in the stator winding structure can give a sensitive indication of degradation processes so long as individual discharge events are detected and measured. The discharge characteristic so obtained is that which the machine exhibits continuously in normal service and is influenced by service conditions such as physical movement which cannot be simulated in an off-line test. Regular monitoring provides the opportunity for early detection of problems and possible remedial action to prolong winding life, or for scheduling of rewind operations during routine shutdown periods. This paper describes an on-line discharge monitoring system which has been extensively applied to machines in service and presents case studies to illustrate the correlation between measured discharge characteristics and winding condition