Tests with High Direct Voltages
HVDC test voltages represent the stress of insulations in HVDC transmission systems. Today, HVDC transmission systems are long point-to-point connections for the transmission of high power. These links are realized by HVDC overhead lines and HVDC cables, especially submarine cables. In the near future, it is expected that the application of the HVDC technology will increase and also HVDC networks will be established (Shu 2010). Therefore, also HV tests as well as PD and dielectric measurements under direct voltage are becoming of increasing importance. Design and testing of HVDC insulation has to be performed under a difficult understanding of the acting electric fields. The reason are space and surface charges which are generated even below the PD inception voltages and strongly influenced by thermal effects. There are many publications on these phenomena, e.g. (Hering et al. 2017; Ghorbani et al. 2017; Christen 2014). This chapter starts with the different circuits for HVDC test voltage generation. Then, the requirements for HVDC test voltages according to IEC 60060-1:2010 and the consequences for the components of test systems are considered. The interactions between test generator and test object are investigated for capacitive load—e.g. of submarine cables—and for resistive load in case of wet, pollution and corona tests. A short description of test procedures with HVDC test voltages follows. Finally, it is described how direct voltages can be measured by suitable measuring systems of resistive dividers and suited measuring instruments, and how measurements—e.g. PD measurements—at DC voltage are performed.