| In recent years,the global energy Internet has been developing continuously.As the backbone of the network,UHVDC Transmission has a serious problem about the space charge inside the DC cable.The accumulation of space charge in the DC cable is more serious than the AC cable.The accumulation of space charge will lead to the distortion of electric field,deterioration of cable insulation,and eventually lead to the aging of cable insulation.In addition,because of the heating of the conductor,the operating temperature of the insulation is high.On the one hand,high temperature makes the insulation aging.And on the other hand,it aggravates the injection of the space charge,which makes the cable insulation deterioration.In order to study the aging problem of DC cable insulation under the electric and thermal field,DC electric-thermal aging of insulation material for XLPE was studied.In this paper,a platform for the electrothermal aging is built.The samples are aging in air and transformer oil respectively at 90°C,104°C and 113°C.After the aging,a series of tests are done such as the space charge distribution at 25℃ and 50°C,the conductivity and dielectric properties of the aging samples and the FTIR analysis.The results show that the aging in the two environments,the air and the transform oil,are different.Samples aging in the transform oil have the hetero-polarity accumulation.And with the aging of the sample,the proportion of deep traps decrease.The conductivity of the sample increase.Permittivity at high frequency decrease while the dielectric loss at low frequency increse.The FTIR shows that there is no obvious oxidation reaction during the aging.Samples aging in the air have the significantly homopolar injection.Some samples even have the charge packet inside.Traps inside the sample are mainly deep traps,and the energy level is higher than the oil aging samples.Conductivity of the aging sample is obviously reduced.The dielectric constant increases at high frequency,and the dielectric loss at low frequency is decrease comparing with the non-aging sample.There is no carbonyl peak in the sample,indicating that the thermal oxygen aging is not intense.The results make a detailed analysis of the DC electrothermal aging.It has reference for online monitoring and life assessment of DC cable. |
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