| With the development of society,cable is used more and more widely.In actual use,under the combined action of many factors,insulation aging will lead to failure,water tree is one of the important causes of accidents.At home and abroad,whether the damped oscillation voltage is effective in the detection of cable water tree is still a stage of debate.Therefore,this paper carries out research on the detection and recognition method of cable water tree based on damped oscillation voltage.The water tree culture model and platform of cable were established,and water tree defects with 50%,70%and 90%length ratio were prepared.The sensitivity difference of damping oscillation voltage and power frequency voltage to water tree defect detection was compared.Combined with DC prepressure time,a water tree severity diagnosis method based on damping oscillation voltage was proposed.The influence of damping oscillation voltage test on the growth of cable water tree under different pressure times and DC prepressure time is explored.The main conclusions of the study are as follows:1)Under the damping oscillation voltage,the detection effect of water tree is more sensitive than that under the power frequency voltage,the PDIV is lower,and under the same voltage,the local discharge of water tree is larger.2)Under different DC bias time,PDIVs of aging defects of water trees with different degrees have saturation effect,and the time required for defects to reach saturation is significantly different with different water tree length ratio,which can be used to diagnose the aging degree of water trees.When the aging degree is more obvious,the lower the PDIV is,and the lower the slope of the saturation curve is,the earlier saturation is reached.The mechanism lies in that during the DC bias process,the charge injected by the electrode and the presence of a large number of ions increase the accumulation of charge,so that with the increase of the aging degree,the channel opens and the conductivity increases.The water tree is easier to capture the charge and the PDIV reaches saturation state faster and has higher discharge capacity.3)Pressure 40 times and DC prepressure after 60s were respectively compared with the control group.The maximum discharge quantity,discharge times and discharge characteristics of the two groups were not significantly different.Slice observation showed that the length and shape of the water tree did not change significantly,and the damping oscillation voltage test would not aggravate the harm degree of the original water tree. |
