Non-intrusive technique for measuring space charges in dc cables

This paper presents space charge measurement technique for dc cables. The principle of the method is measuring a current representative of space charge after applying a thermal step in the cable insulation. For long cables, thermal step method allows the measurement of space charge by perturbing the electrostatic balance using Joule effect in the conductor. The thermal conduction into insulation causes a locally and temporarily modification of electric properties and the circulation of displacement current between the core and outer screen. This paper presents procedure for sizing the power pulse needed to apply the thermal step method. Experimental results obtained using mini-cable confirm space charge measurements in a non-intrusive manner.