HVDC cable design and space charge accumulation. Part 3: Effect of temperature gradient

An investigation was conducted on the extent of space charge accumulation due to a temperature gradient in comparison with other charge-supply mechanisms, especially injection from the electrodes. In order to realize the feat, space-charge measurements were conducted out on HVDC cable models under application of different temperature gradients across the cable insulation, above and close to the threshold field for space-charge accumulation. Results show that in space charge generation in HVDC cable models at low fields, nonuniform conductivity due to a temperature gradient can play a role, not too far from the threshold for space-charge accumulation in samples with a uniform geometric field, especially if cable insulation thickness is huge. In addition, blocking and injection of charge at the electrodes may prevail over bulk charge accumulation produced by a temperature gradient, if the electric field is considerably larger than the threshold.