Research On The Method Of Detecting And Evaluating The Insulation State Of Building Power Supply And Distribution Cable

As an essential power transmission equipment in the power supply and distribution system of modern buildings,power cable is the artery of building cluster and even the whole city function.XLPE cable is widely used as building power supply and distribution cable,its insulation performance is faced with the risk of continuous decline in the long-term operation of the cable.Once the insulation failure of XLPE cable for building power supply and distribution occurs,it will lead to power interruption of the whole building power supply and distribution system and bring negative impact on production and life.Therefore,in order to ensure the building electricity demand and maintain the stability of the building power supply and distribution system,it is necessary to regularly conduct insulation detection and aging assessment of power cables.Thermal aging caused by temperature is the main reason for insulation failure of power supply and distribution cables in buildings.As a nondestructive testing technology,frequency-domain dielectric spectroscopy test results are highly sensitive to temperature and insulation aging,which can realize the insulation performance diagnosis of XLPE cables without damaging the cables.In order to study the insulation aging of XLPE cable for power supply and distribution in actual building,this paper made the XLPE cable sample with the same effect as the building power supply and distribution cable,and carried out accelerated thermal aging test on the sample.The XLPE cable samples with different aging periods were tested by frequency domain dielectric spectrum at different temperatures,and then the effects of aging and temperature on the test results were studied,equivalent circuit model and dielectric response mathematical model are used to fit the measured data.A multi-objective genetic algorithm combined with heteroscedasticity test is proposed to ensure the significance of the model and achieve optimal solution at the same time.The variation of dielectric response model parameters with temperature and aging was studied,and the life of XLPE cable insulation aging is evaluated by relaxation time and dielectric loss integral value of high and low frequency band.In order to further eliminate the influence of temperature on the measured results of frequency domain dielectric spectrum,the temperature characteristics of polarization and conductance were studied by using the theory of potential barrier and transition state,and temperature normalization was carried out for the measured results of different temperatures under the same aging state.In order to realize the remote diagnosis of local insulation aging of building distribution cables,the influence of local insulation aging on the input impedance of cable head end was studied by using simulation technology.The relationship between the dielectric response information of XLPE insulation and the input impedance of the cable head end is established.Then,multi-objective genetic algorithm combined with heteroscedasticity test was used to evaluate the local insulation aging state of power supply and distribution cables in buildings.The research shows that: there is a good mapping relationship between frequency domain dielectric spectrum test results and insulation aging of power supply and distribution cables in buildings.Multi-objective genetic algorithm combined with heteroscedasticity test can realize the optimal solution of equivalent dielectric response model of XLPE cable.By solving the input impedance equation of the cable,the local insulation aging characteristics of XLPE cable can be extracted,and the remote diagnosis of power supply and distribution cables can be realized.Using the theory of temperature normalization can eliminate the influence of temperature and further evaluate the results accurately.