Design Of Acoustic Detection System For Aging Defect Of Grounding Insulation Of Generator And Research On Aging Properties Of Stator Bar

Stator winding insulation of generator will be subjected to the effects ofelectricity, heating, mechanical vibration, and environmental factors duringoperation and it will be gradually aging. Over time, the insulation have theprobability of breakdown and then the generator can’t operate normally.Therefore, to find out characterization of insulation aging has very importantsignificance on generator reliability and safe operation. Currently, mostcharacterization of insulation aging performance are the electrical parameters,but they could not fully reflect the insulation structure variation with aging time,so we have to find out an accurate, simple and reliable method to detect thedefection of insulation.In this paper, the characteristics of forced vibration of an insulation plateand its acoustic wave propagation in air and insulation are studied on the basis oftheoretical acoustics. An acoustic detection system for grounding insulation ofgenerator were manufactured based on virtual instrument technology. In order toobtain the characteristics of the material and interior structure of detected object,a mechanical impact was exerted against the object surface, is used to generatelow frequency wave and acoustic wave produced by the object is receivedthrough the highly sensitive microphone and analyzed by the computer. Theanalysis method includes time domain analysis and frequency do main analysis.As the acoustic wave carry internal defect information of insulation, the acousticdetection method could be used to diagnose the aging state.Three bars are aging with electric、heat and electric-heat stress for1000hours of four cycles. The detection system has the feature of small size and lightweight and could detect the defection of insulation. Acoustic testing and electrical test were carried out after every aging period, the experimental resultsshow that the main frequency of the acoustic detection signals decreasesgradually with the aging time increased; The increased magnitude of dielectricloss tangent values is different under the different aging factor; PD capacity andtimes of two-factor aging bar are more than single-factor aging bar’s; Finally,bars are cut at the spot where the main frequency of the acoustic detection signalsdecreases significantly; From the observation of the cross-section of bars, we cansee that electrical-thermal aging bar has the significantly delaminations, it meansthat the acoustic detection system could detect the defection of the bars. Theelectrical parameters and acoustic parameters could be co mbined to detect thedefection of insulation and it could also improve the detection accuracy.