Influence of high-voltage loop inductance and proximity effect on the performance of a 1000 kV damped capacitive LI divider

During a bilateral comparison of lightning impulse measurement systems, an unexpectedly large discrepancy in the T1 time parameter error was found in a 1000 kV damped capacitive divider used by VTT MIKES. The only difference in the measurement setup between the comparison measurements and a calibration of the same divider two weeks prior was the high-voltage loop size and the addition of another tall voltage divider in the vicinity, the reference systems were kept the same in both occasions. This sparked the interest to find out to which extent the high-voltage loop size and proximity effects influence the T1 error. During follow-up measurements and analysis of the comparison data, the value of T1 turned out to have the major influence on the T1 error. Longer T1 waveforms showed larger errors than shorter ones during the LI measurements. The high-voltage loop size and proximity effects showed only a minor impact on the error. This finding was further backed up by convoluting ideal LI-waveforms with the measured step response of the 1000 kV divider and the T1 errors showed a similar dependence on the value of T1 as in the real measurements. These results are also in line with previous work done on the same topic. This work shows that in this case, the step response of the divider has a far greater impact on the error than the high-voltage loop size and proximity effects. The key to improving the performance of the 1000 kV LI divider is to tune the step response of the divider even further. The measurements also revealed a high-frequency disturbance present in the 1000 kV divider, the source of which were investigated but not found.