Research On Assessment Method For Insulation Aging State Of XLPE Cables

The XLPE cable has been more than40years’operation history in China. A lot ofresearch show that the degradation of XLPE cable insulation is not the result of asingle factor, but a variety of factors such as electrical stress, thermal stress andenvironmental effect. The operating cable insulation degradation conditions is alwaysthe focus of attention of the grid operation corporation, but at present, most studies ofXLPE cable insulation degradation is new cable which is never put into operation inChina and abroad, the study of performance of operating XLPE cable insulationdegradation is less. The dielectric and physicochemical characteristics of XLPE cableinsulation varies with its aging state obviously. Therefore, the test of the dielectricproperties, physicochemical properties and power frequency breakdowncharacteristics of XLPE cable insulation before and after aging is necessary. Themeasurement of these parameters can be used as an effective method for aging stateassessment of operating XLPE cable. In this paper, the research contents andachievements are as follows:1. It studied the relationship between the dielectric properties, physicochemicalproperties and the aging state of XLPE cable insulation. The dielectric properties,physicochemical properties will change with the influence of electrical stress, thermalstress and environmental effect, etc. The influence of electrical stress, thermal stress isthe most important. The measurement of these parameters can be used as an effectivemethod for aging state assessment of XLPE cable insulation.2. The method for aging state assessment of XLPE cables are studied, includingdielectric loss (tan δ), fourier transform infrared spectroscopy (FTIR), oxidativeinduction time (OIT) and breakdown voltage. The dielectric and physicochemicalproperties of XLPE cables before and after aging are analyzed. The experimentalresults indicate that the dielectric loss of XLPE insulation、oxidative induction time,carbonyl index and breakdown voltage have good consistency in terms ofcharacterization of the cable insulation degradation performance. The dielectric lossincreases, oxidative induction time decreases, carbonyl index degradation increasesand breakdown voltage decreases when the cable insulation degradation occurs.3. The dielectric loss spectrum (especially in the low frequency region) of XLPE cable insulation is significantly associated with its aging state. The method is accurate,quick and can be used to accurately characterize the degree of aging state. Thedisadvantage is that it can only reflect the overall degree of aging and the equipmentis expensive and difficult to promote. The test of oxidative induction time andcarbonyl index can qualitatively assess the degree of thermal aging. But the testprocedures are complex. The test of tolerance time is better than the breakdownvoltage in the assessment. This method is simple and effective, suitable forengineering applications, but multiple measurements are necessary to reduce the error.