A procedure for space charge measurements in full-size HVDC extruded cables in order to access the electric field in the insulation wall

This paper proposes a procedure for the measurement of space charges in full-size HVDC extruded cables, that accounts for the experimental practices of such kind of measurements in terms of poling time, depolarization time, heating and cooling of specimens. The aim is to access the electric field in the insulation wall under different test conditions. Such procedure to be used in prequalification tests can give the fingerprint of the tested cables and the results could be useful in order to skip the prequalification tests on new cables manufactured with the same insulation and semiconductive compounds, but with different cross section geometry. It must be pointed out that there is no universal agreement about limits for space charge measured. However the change in the relevant electric field with respect to the Laplacian field seems a clear indication of the attitude of an insulation to give rise to field enhancement, and thus to behave unsatisfactorily in service. In any case, the aim of the procedure is not giving maximum acceptable space charge limits, but rather evaluating the electric field profile during the prequalification tests in full-size HVDC extruded cables.