Study On Nondestructive Lifetime Prediction Method Of EPR Insulation Material In Shipboard Power Cables

As the core of power energy transmission and distribution,the insulation aging degree of shipboard power cable is significant for the working security of cable and operational reliability of electric equipment.The working condition of shipboard power cable is very complex,including temperature,oil mist and humidity,which accelerated the thermal aging of insulation and reduce the service lifetime.Therefore,it is necessary to study on the lifetime prediction method in order to ensure security operation and maximize cable lifetime.This dissertation mainly focused on the ethylene-propylene rubber(EPR)insulation is the higher utilization in shipboard power cables,and the varying tendency of physical properties,chemical properties and electrical properties of EPR insulation under accelerated aging was determined.Then the relationship between hardness retention rate(P%)with interval value integral of the dielectric loss tangent among O.OlHz-lHz(tan?int)and elongation at break retention rate(EAB%)were discussed.The nondestructive life termination index based on P%and tan?int,were obtained,and the operating temperature in the lifetime prediction model was analyzed.The main contents of this paper are as follows:A research on the relationship among tensile strength,EAB%,stress and tensile deformation of EPR insulation material in the hygrothermal aging and thermal aging condition shows that temperature had a significant effect on the aging of EPR than water.The EAB%and Fourier transform infrared spectrometry under thermal aging were analyzed,and the results showed that EAB%was decreased along with the increase of aging degree,and the change rule was the same with transmission peak at 1790cm-1.The shift factors were optimized through regression equations,then obtained the fitting equation of EAB%at the reference temperature.Moreover,an extrapolation equation for lifetime prediction of EPR insulation material was established according to the Arrhenius equation.The relationship between EAB%and P%was analyzed by experimental data and theoretical calculation,which shows that the change rule of curve was the same and P%can be used as the EPR insulation aging characteristics.The P%reduced to 10%was proposed as the lifetime termination index when EAB%reduced to 50%according to IEC 60216.The lifetime difference was analyzed between EAB%and P%when they reached lifetime termination index,the result shows that the maximum lifetime difference is small,and it proved the validity of lifetime prediction of EPR insulation material based on P%.The changing characteristics of the frequency domain spectroscopy(FDS)were analysed at different aging condition,and the results showed that the value of FDS at the frequency range from 0.0l Hz to 1Hz increased monotonically.The lifetime prediction equation of EPR insulation was established based on tan?int by chosen tan?int as the aging characteristic value of EPR insulation.Tan?int equal to 0.5 was proposed as the lifetime termination index when EAB%reduced to 50%.Comparison with lifetime prediction value between EAB%reduced to 50%and tan?int equal to 0.5,and the results show that the lifetime prediction values are identical under different temperatures,which proved that tan?int can be chosen as an effective method to predict lifetime of EPR insulation material.The working temperature of cable at different load current was obtained according to establish three-dimensional finite element simulation model.There is a wide variation between the simulation working temperature with fixed parameters and the measuring temperature under simulated real operation condition.In the case of single increase of the thermal conductivity of insulation and sheath layer,the effect of thermal conductivity on the conductor temperature was studied.The thermal conductivity of insulation and sheath layer calculated at different load current based on the steady state heat conduction model of insulation layer,and the relationship between the thermal conductivity and the load current was derived.The result shows that the simulated temperature under varied parameters was close to measured temperature after changing thermal conductivity.According to the measure values of P%and tan?int of EPR insulation material of 30 years-old shipboard power cable,the correction coefficient of actual working times and remaining lifetime were deduced by corresponding lifetime termination index.The result shows that both of two methods have small error and its can be used to evaluate the insulation state and lifetime prediction of shipboard cables.