Evaluation of Electric Field in a DC Model Cable During Superimposed Impulse Voltage Tests

Superimposed impulse voltage tests are performed as a part of the qualification of HVDC cable systems. The electro-thermal preconditioning prior to the impulse tests may lead to the accumulation of space charges in cable insulation, which eventually affects the resulting electrical field. Such an impact was evaluated in this work using the bipolar charge transport model with inclusion of ionic charge carriers. The results show that the preconditioning gives rise to the inhomogeneity of the electrical stress, specifically it leads to an electric field enhancement near inner radial position during the impulse tests of opposite polarity and near outer radial position under impulse tests of same polarity. Contribution of cable temperature and the generation and transport of ionic charges were thereafter studied and discussed.