Research On The Aging Evaluation Method Of Dry-type Transformer Based On Dielectric Spectroscopy And Activation Energy Characterization

Transformers play an increasingly important role in modern power networks.However,under the combined effects of heat,electricity,machinery and environment,the insulation systems are gradually becoming aged,which may lead to serious accidents and huge losses.However,due to the current large-scale transmission network construction,many studies are mainly focused on oil-immersed power transformers with insufficient research on dry-type transformers that also undertake power distribution tasks in the power grid.The epoxy cast dry-type transformer insulation material is mainly made up of epoxy resin,and much attention is attached to the modification without the evaluation of its aging state.In the existing standards,mass loss is used as a reference for the aging assessment of epoxy resin,but the acquisition of mass loss in the actual operating transformer lacks practicality.Therefore,it is necessary to consider new characteristic parameters to evaluate the aging state of the material,and then to realize the evaluation of the insulation aging state of the dry-type transformer.In order to make up for the shortcomings of the existing research,this paper proposes to apply the activation energy to evaluate the aging state of the epoxy resin used in dry-type transformers.For the purpose above,an accelerated thermal aging platform and frequency-domain dielectric spectrum test platform were respectively set up in the laboratory.Firstly,under the conditions of laboratory,the epoxy resin specimen was subjected to accelerated heat aging test at three temperatures,and the mass loss and dielectric properties were periodically sampled and tested.Then,the existing standard of quality loss rate was referred to confirm the time when the epoxy reached the aging failure state.It is found that under the temperature of 150?,170?,200?,the time for the epoxy resin to reach the condition of failure is 12.4a,7.95a,5.35a.Then,the frequency-domain dielectric and temperature spectrum of the samples under different aging conditions were obtained.The activation energy of epoxy resin samples under different conditions was calculated by dielectric response method,and the effects of temperature and aging degree on activation energy were analyzed.The exponential decay relationship between activation energy and aging time was established,and the aged activation energy of epoxy resin was confirmed,which was 1.63E-3eV for 150?,5.67E-4eV for 170? and 5.44E-4eV for 200? under the laboratory condition.And based on the temperature acceleration factor AFT proposed by Arrhenius,the aging time under laboratory conditions was equivalently converted to the actual transformer running time to achieve the life prediction of dry-type transformers.In this paper,the activation energy that characterizes the reaction rate in chemistry is used to evaluate the aging reaction,and the mature dielectric response method is used to obtain the activation energy of different aging stages.With Arrhenius's temperature acceleration factor AFT,a method for evaluating the aging state of dry-type transformers using activation energy is proposed,and the aging time calculated in the laboratory condition is associated with the on-site running time,which provides a new reference for the accurate assessment of aging state of the ary-type transformer in the field.