| The content of this paper is an important part of “High voltage motor main insulation condition monitoring and method of early warning”(No:2014011024-3), sponsored by the Natural Science Foundation of Shanxi Province. The task is mainly proposed for the high-frequency problem of stator insulation fault of high voltage(HV) motor. Stator winding insulation, suffering from thermal, electrical, mechanical and ambient stresses in HV motor in the long term operation, which decreases mechanical properties and electrical strength and leads to partial discharge(PD). PD is one important of indicators evaluating insulation aging conditions. According to statistics, over 40% of HV motor failures are caused by stator insulation degradation. Therefor, there is very important significance to research the changes of PD features under multi-factor aging, analyze each aging factor on the influence of PD and understand the mechanism of different PDs.The stator winding insulation always suffers from a variety of aging stresses,and many types of PDs are produced due to the different combinations of stresses. Many multi-factor aging models have been applied to simulate the insulation aging process and achieved remarkable results for a long time.However, the stresses are almost electrical, thermal and mechanical. In fact, in addition to the above aging stresses, the ambient, such as humidity,oil-contamination, chemical erosion, is occupying an important position in the stator wingding insulation aging fault with the HV motor working environment more complex, which leads to a variety of insulation faults including PD. Two multi-factor aging models, applied to end-winding and slot of the stator windingrespectively, have been developed in this paper, and with these the aging tests of stator winding on 10 k V motor have been carried out and achieved significant aging effect. Thereinto, the end-winding aging model is made through combining with thermal, humidity, electrical, oil-contamination and abrasion,the slot part aging model is made through combining with thermal, electrical and abrasion.Different aging degrees of insulation correspond to different PD signal. In order to accurately extract the PD signal, some new stator windings are used as experimental object, and a mockup stator core with two slots is developed to serve as the grounded electrode. Through these measures, the interferential discharges are exclude and ensure the reliability and uniqueness of the partial discharge.On the basis of multi-factor aging models and test methods, the PD signals are extracted. Through measuring the characteristic parameters including phase resolved partial discharge(PRPD), PD current(NQS), PD power(P), PD phase,PD number, PD asymmetry, the stator winding insulation aging condition can be predicted. Some laws have been found that amplitude and phase distribution of PD characteristic parameters are different and unique under different aging conditions through the analysis of parameters.The occurrence and development, as well as the mechanism of end-winding discharge and slot discharge are analyzed through analyzing the relationship between the PD parameters and the aging conditions. And the impact of each aging factor on PD has been summarized. It is found that mechanical abrasion is the prerequisite to cause the end-winding discharge and slot discharge and temperature significantly promotes the process of discharge. The development of the oil-contamination discharge depends on the size of humidity and voltage, the discharge will be inhibited when the humidity and voltage are within a certain range and humidity plays a significant role to suppress the discharge, however,when the humidity and voltage are more higher, creeping discharge will generate and the insulation on the discharge area will be carbonized, insulation degradation and insulation fault for a long time of creeping. |
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