Characterization of the voltage non-linearity of a 1200 kV HVDC divider

The report describes the methods used and results of a characterization of the voltage non-linearity of a 1200 kV HVDC divider at Aalto University high voltage laboratory. Measurements were performed in April 2012 and June 2013. Historical data from 1990 and 2007 were combined with new measurement results to gain good understanding of the voltage dependence and its reasons. The new more precise measurements confirm the findings of the 2007 measurements. The results show that the scale factor of the divider has a linear relative voltage dependence of 0.2 %/MV. It was also found that the oil-filled high voltage resistors have a thermal time constant of several hours.