CHARACTERISTIC ELECTRONIC SIGNATURES FOR WET INSULATION

摘要

Recently, there have been reports that there is a characteristic signature for wet stator insulation, observable via Electro-Magnetic Interference (EMI) methods. This signature reportedly has a frequency of 2-5 MHz, is random noise, can be detected at or away from the line side, and is only observed on General Electric (GE) machines. A series of controlled experiments were conducted to investigate this. Two different sets of tests were conducted. The first test was conducted on a water-penetrated, 20 year old GE stator bar. The water penetration was monitored for its location and the amounts were quantified. Simultaneously, phase-resolved Partial Discharge Analysis (PDA), Electromagnetic spectrum analysis (ESA), 60 Hz current and acoustic monitoring was also performed. A second, more controlled test, was performed by placing a wet insulation layer in the center of a "sandwich" of dry insulation and measuring the electrical responses under application of 60 Hz high voltage. Regardless of the test, we found no unique electronic signatures related to water presence in or impregnation into the insulation, under the grading paint, and under the armored region of the stator bar. There appears to be nothing unique or discriminating about the frequency or the random-nature of the events. No random noise signatures were noticed. However, corresponding with increased water penetration, there is an increase in the 60 Hz current loss within the insulation as well as a noticeable decrease in the electrical discharge activity. Additional literature references are cited supporting the results of these controlled experiments. Alternative, reliable technologies are mentioned for wet insulation detection and monitoring.