Modeling the electric field in polymeric insulation including nonlinear effects due to temperature and space charge distributions

摘要

High Voltage Direct Current (HVDC) cables are often insulated with cross-linked polyethylene (XLPE) or low-density polyethylene (LDPE). Space charges occur by injection of charges, ionization of impurities, polarization, or by permittivity-over-conductivity changes. Under HV application, heterocharges accumulate in the neighborhood of each electrode and contribute to the reduction of the breakdown voltage, whereas the accumulation of homocharges tends to cancel the resulting field enhancement. The knowledge of the electric field and hence, the space charge distribution inside the insulation, is necessary for the assessment of the reliability of the insulating material. To simulate the electric field, a conductivity-based charge-model is developed. Spatial variations of charge distribution result in conductivity changes. The simulation results conform well with published measurements, meaning that the introduced model constitudes an alternative to more complex charge-models.