Frequency Domain Dielectric Response Characteristics And Condition Evaluation Method Of Transformer Oil-Paper Insulation

The transformer is the core equipment for energy delivery and distribution inpower system. How to evaluate the exact aging condition of transformer insulation andimprove the safety operation level has become an urgent technical problem for powerdepartment. Frequency domain spectroscopy technology, based on the principle ofdielectric response, has the advantage of non-destructive measurement, user-friendlycontrol and strong anti-interference ability. Thus, it is used as the diagnostic tool forcondition evaluation of oil-impregnated transformer by scholars at home and abroad.But it is currently limited to the evaluation of moisture content and oil conductivity,rarely seen used in aging state diagnosis. Exploring a new method or characteristicparameter that can be applied to diagnose moisture content and aging status oftransformer main insulation will be of great academic significance and applicationvaluable.The oil-paper insulation thermal aging and frequency domain dielectric responsetest platform are developed, and the related experiments are designed in this paper. Theimpacts of various factors, such as oil conductivity, moisture content and aging level,on frequency domain spectroscopy of oil-impregnated pressboard are quantitativelyanalyzed. The changes of frequency domain spectroscopy of the transformer maininsulation system under different conditions are simulated based on XY model, whichfeatures main insulation structure. And the evaluation procedure of moisture contentand aging condition of main insulation is set up combined with XY model simulationand frequency domain characteristic parameters. Finally the validity of the method isverified by the site diagnosis example. The main achievements made in the paper areas follows:①A new method used to evaluate the moisture content and aging condition ofoil-impregnated pressboard by its dissipation factor value of characteristic frequency isput forward. According to the phenomenon that the tanδ spectroscopy varies atdifferent frequency ranges under the influence of moisture content and aging, themoisture content and aging condition of pressboard can be quantitatively assessed onthe basis of the exponential function relationship between tanδ at characteristicfrequency and its corresponding insulation status.②The “frequency-temperature-shift” method is used to shift the tanδ spectroscopy of oil-impregnated pressboard at a different temperature to the samemaster curve. And the tanδ spectroscopy of the main insulation system at anytemperature can be calculated from that of pressboard and oil conductivity at onetemperature. Thus, the influence of temperature on measuring results can beeliminated.③The XY model is used to build the connection between the frequency domainspectroscopy of single oil-impregnated pressboard and that of the transformer maininsulation system. The XY model simulation results show that: oil conductivity has agreat influence on the shape of tanδ spectroscopy; The frequency range and variationlaw of tanδ spectroscopy under the influence of geometric structure and moisturecontent have a great relationship with oil conductivity; The tanδ spectroscopy of maininsulation system shifts to higher frequency due to the aging of oil, and the aging ofpressboard increases the tanδ spectroscopy in lower frequency zone, when aged to acertain extent, a “wave crest” appears in the tanδ spectroscopy.④The frequency domain spectroscopy of pressboard in transformer can bededuced from field measurement of the transformer main insulation system using XYmodel simulation. And according to the proposed characteristic parameters formoisture content and aging condition evaluation of oil-impregnated pressboard, thecondition assessment of the transformer main insulation system can be elementaryrealized.