Qualification of MVAC XLPE Cables for DC Operation

As a consequence of the energy transition, DC transmission in the medium voltage level is becoming ever more important. Decentralized energy production and rising energy consumption are the main reasons for the increasing interest. One approach is the conversion of MVAC cable systems to MVDC cable systems or to use new MVAC cable equipment in MVDC cable systems. It is first necessary to establish a qualification procedure for MVAC cable systems under DC stress, however, as there is none available at present. The MVAC cables and accessories are thus investigated with multiphysical FEM simulations. The FEM simulations include measured temperature profiles from the accessories to receive a realistic temperature behaviour in the thermal-electric simulations. The conductivity of the cable insulation (XLPE) is taken from leakage current measurements. The simulations show time constants for the field transition in the cable in the range of minutes and electric fields in the cable system under 13 kV/mm for VDC = ±55 kV. Furthermore, this contribution provides a proposal for a qualification procedure for MVAC cable systems used as MVDC cable systems, which includes FEM simulations, partial discharge, leakage current, space charge measurements and breakdown tests.