A New DC Test System for Testing Extra Long Cables

Abstract:
State of the art DC test systems (cascaded or called Greinacher or Cockcroft Walton) provide test voltages up to and above 1000 kV at a maximum DC current of around 100 mA. In case of testing extra-long HV DC cables, having a load capacitance in the range of several tens of muF this leads to charging times of several hours or days, while the test duration of 1 h according standards gets neglectable in comparison to the charging time. After the test duration, the cable remains charged and requires a sophisticated procedure to be discharged. Usually this discharge procedure requires access to the HV room with special protection measures. The DC test systems presented here over-comes several of these draw backs in one unit: The system provides a charging current of up to 10 A, allowing to charge an extra-long cable up to test voltage in about 1 hour, and then maintaining the test voltage for 1 hour. After the test duration, a remote-controlled discharging of the cable can be invoked to discharge the cable to almost down 0 kV within a time frame of less than 1 h. No entry of the test room is required, no water resistors are used. The energy stored in the cable is dissipated via the power electronics into the ambient air. The paper explains the general setup of the test system and its components. The benefits of this approach and its draw backs are discussed.