Research On Failure Mechanism Of Interturn Insulation Of Dry-Type Air-Core Reactor Under Overvoltages

Dry-type air-core reactors are widely installed in the power system for limiting current,filtering,and reactive power regulation.The interturn insulation breakdown caused by insulation aging during operation,even burning accidents,is the main failure mode of the dry-type air-core reactor.Overvoltage and its electrical aging,as the main factors causing the degradation of insulation performance,have been the focus of research in the engineering field.There are few reports on the systematic research on the causes of the overvoltage of dry-type air-core reactors,the laws followed,and the failure mechanism of interturn insulation under the overvoltage.This paper mainly studied the switching overvoltage of dry-type air-core reactors and the deterioration law of interturn insulation under the switching overvoltage.The main work is as follows:The three-phase simulation model and theoretical analysis circuit were established to study the causes of the overvoltage and the law it follows in the process of a circuit breaker breaking a dry-type air-core reactor.Typical waveforms of overvoltages were obtained by simulation,and the influence laws of various related parameters on overvoltages were analyzed.The mathematical models of the maximum chopping overvoltage and the reignition overvoltage were obtained by the combined method of simulation,theoretical analysis,and data fitting.The research results provided a theoretical basis for the parameter setting of the overvoltage protection for dry-type air-core reactors.A model specimen of interturn insulation was produced for the degradation law of interturn insulation of dry-type air-core reactors under accumulative switching overvoltage.The accumulative test device of exponential decay oscillating overvoltage was designed and built.The variation of insulation performance parameters of model specimens with the accumulative number of overvoltages was measured,such as partial discharge characteristic parameters and insulation resistance.Also,the variation of the breakdown voltage with the amplitude of accumulative switching overvoltages was measured.And then the degradation mechanism of the interturn insulation under the accumulative effect of overvoltage was analyzed.The research results provided a theoretical support for the design of the insulation structure for dry-type air-core reactors.The accelerated thermal aging test of specimens was carried out to further the research the effect of thermal aging on the interturn insulation properties to withstand switching overvoltage.In the test,the variation of the accumulative number of switching overvoltages was explored for model specimens with the degree of thermal aging.According to the variation of the electrical properties of the model samples and the mechanical properties of the polyester film with the degree of thermal aging,the influence mechanism of thermal aging on the characteristics to withstand the switching overvoltage of interturn insulation was analyzed for dry-type air-core reactors.The results lay the foundation for the further research on the degradation mechanism of interturn insulation under the combined effect of multiple factors.In order to obtain the electric aging life model of the interturn insulation for dry-type air-core reactors under the power frequency overvoltage,the accelerated electric aging test of the interturn insulation model specimens was carried out by constant voltage method and step voltage method,and the electric aging inverse power life model is established under two ways of applying voltage.Based on the electric aging mechanism of the interturn insulation under the condition of the power frequency overvoltage,the causes of the difference between two life equations were analyzed and verified by experiments.The inverse power life equation of the power frequency electric aging under the condition of the power frequency overvoltage was corrected for the interturn insulation of dry-type air-core reactors,and the accuracy of the modified equation was verified by experiments.This provided a more accurate method for the life prediction of dry-type air-core reactors.The research results in this paper can provide the theoretical support for the optimization of the interturn insulation design of dry-type air-core reactors and the improvement of the production process for manufacturing enterprises,the improvement of the operation mode of dry-type air-core reactors and the development of the overvoltage protection devices for the electric power operation departments.