Electric fields in LVDC cables

The operation of legacy LVAC distribution cables under DC is considered in this work. The electric field distribution in cable insulation under DC voltage is governed by the electrical conductivity of the material unlike the AC case where it is dependent on the permittivity of the materials. Temperature, water ingress and chemical ageing can increase the conductivity of the insulation. A good insulator should exhibit the least conductivity possible in order to minimise the current flowing through the material. Variations in insulation properties leading to reduced uniformity could cause local elevated stresses in the insulating material which could lead to cable failure. This paper shows how the electric field distribution in typical LVAC cables changes as the conductivity of the insulation is altered due to changes in temperature and electric field when operated under DC. A 4-core Paper Insulated Lead Covered (PILC) belted cable is simulated in COMSOL Multiphysics both under AC and DC conditions and the results are compared.