Study On Low Temperature Dielectric Characteristics Of Oil-immersed Inverted Current Transformer

In recent years,with the continuous development of China’s power grid,the number of HV and UHV lines in Northeast,Xinjiang and Inner Mongolia is increasing.The operation of power equipment in the cold environment is facing severe test,among them,the inverted oil-immersed current transformer is the core measuring equipment in the power system,its safe and stable operatio n is very important to ensure the reliability of power grid.Therefore,based on the oil-paper insulation model,this paper analyzes the dielectric characteristics of the inverted oil-immersed current transformer at low temperature.This paper is based on the theory of dielectric response,using the modified Cole-Cole model to extract the characteristic parameter α of oil-paper insulation model and inverted oil-immersed current transformer,characterization by characteristic parameter α and change rule of temperature and aging days,conduct quantitative analysis.Secondly,this paper combines the basic theory of frequency temperature translation,the oil-paper insulation model with different aging days and the activation energy of the oil-paper insulation system inside the inverted oil-immersed current transformer are calculated.Meanwhile,using the characteristic that activation energy does not change with temperature,in the actual test,frequency domain dielectric spectrum curve by testing a single temperature,calculate the frequency domain dielectric spectrum curve at other temperatures.Last,in this paper,dielectric spectrum,conductivity,moisture content and polymerization degree of oil-paper insulation model aged for different days are tested in frequency domain.Meanwhile,the frequency domain dielectric spectrum and power frequency high voltage dielectric loss of the inverted oil immersed current transformer are tested and verified.The test results show that the oil-paper insulation model and the inverted oil-immersed current transformer have similar change rules.With the decrease of temperature,the low-frequency loss decreases and the high-frequency loss increases.The characteristic parameter α is used for quantitative analysis.With the increase of aging days,α decreases gradually.After frequency temperature translation,the 0 ℃ curve is used as the reference for translation,and the frequency-domain dielectric spectrum curve at other temperatures has good coincidence after translation.Because the inverted oil-immersed current transformers in actual operation are all live high voltage operation,therefore,high voltage power frequency dielectric loss test shall be carried out for inverted oil-immersed current transformer.In this paper,by comparing with the frequency domain dielectric spectrum(140V),it is found that there is a quantitative conversion relationship,the calculated results are in good agreement.Therefore,in the following low temperature test of inverted oil-immersed current transformer,the dielectric spectrum curve in frequency domain and the dielectric loss value in high voltage power frequency can be calculated by testing the dielectric spect rum curve in frequency domain at any low temperature,the research results have important practical significance in engineering.