Alternative discharge methods of HVDC cables for a DC test

Abstract: The purpose of this thesis is to analyse alternative discharging methods of HVDC cables for a DC test in a real situation. It is necessary to research relevant data and consult contacts in order to solve the task. The project is based on the implementation of a developed system on the testing object and preceded by tests in the High Voltage Laboratory in Karlskrona. Simultaneously the main requirement is to completely exclude any human contribution in the discharging process of the DC cable and to maintain the highest safety standards in line with ABB policy. Currently the discharge process after DC testing is completed manually. Testing is carried out by increasing the voltage until the test voltage is reached and kept constant throughout the test period. Followed by switching off the voltage and allowing the cable to initially self-discharge, before it forces the discharge through the discharging water resistor. When the voltage is zero, cable termination ground by providing a secure grounding. Initially the cable charges out through self-discharge and this must continue down to the Uo. To avoid damaging the test object by maintaining the voltage for too long, discharge can begin after 45 minutes if the voltage drops below under 1,2 Uo. The forced discharge occurs by an earth rod connecting the discharge resistance to the ground. Past tests have shown the occasional use of a linked up Water Conditioning Unit system consisting of the pump and filters to ground out by hoses filled with deionized water. This method has been reviewed and modernized which made it more accessible and reliable.