Monitoring And Evaluation On Insulation Condition And Grounding System Of Operating XLPE Cable

The XLPE cable has been more than40years’ operation history in China, Theoperating cable insulation degradation conditions is always the focus of attention ofthe grid operation corporation, but at present, most studies of XLPE cable insulationdegradation is new cable which is never put into operation in China and abroad, thestudy of performance of operating XLPE cable insulation degradation is less. Inaddition, Due to the operation peristalsis, poor circumstance, external force damageand other causes lead to the grounding system of XLPE cable metal sheath losteiffcacy, Also can caused cable abnormal heating, reduce current carrying capacity ofcable, and even caused the cable breakdown when being serious. In this paper, theresearch contents and achievements are as follows:1.It has established the quantitative relation between aging status of Cross-linkedcable insulation and residual charge.Via the return of XLPE insulation applied5.9kV/mm electric field and heat cycle experiment accelerated water-tree test, go through4,6,12months atfer aging, The samples of insulation applied direct voltage, then usepulse voltage release space charge of water-tree, and calculate the space chargeamount which is related to water-tree aging. The experimental results indicate that,space charge amount is closely related to the amplitude of direct voltage and ageingtime. The pulse frequency increased from0.8kHz to1.6kHz, the space chargeamount firstly increase then decrease, reached the peak at1.2kHz.2.According to the analysis method of thermo gravimetric, infrared spectrum,mechanical strength test, using the return of llOkV and220kV cross linkingpolyethylene cable as sample, it has proved that the start decomposition temperature、carbonyl index and fracture energy of cross linking polyethylene insulation in termsof characterization of the cable insulation degradation performance has very goodconsistency. Also analyzed the historical operation data of return cable of insulationexisting deterioration, the results indicate that XLPE cable insulation deterioration isclosely related to the heat effect produced by crossing the fault current and otherfactors.3.According to the grounding current online monitoring data of220kV,110kV cableand cable load data as the basis, analyzed normal、abnormal and defect these threekinds of situation of high voltage cable grounding system, then propose three kinds oftypical characteristics model of grounding current. On this basis, via establish mathematical model and calculation sotfware which is developed to analyze its factorsof characteristics and influence, and then correct the condition evaluation results ofhigh-voltage cable grounding system, and propose the improvement strategies ofcondition evaluation of high-voltage cable grounding system.4. For actual situation of operating high-voltage cable and laying channel,studied functional specification, system architecture, communication protocols, statusinformation display and etc. of cable network operation monitoring system of containthe cable insulation, grounding system, operating environment and various parameters,based on above indicated as theoretical support, and built the first domestic cablenetwork operation monitoring center.