Traditionally, leakage current measurement is carried out in
insulators energised at the nominal voltage throughout by a
suitable power supply. The sensor is connected in series
with the insulator and the leakage current is measured
through a shunt resistor or current transformer. Leakage
current value depends on the variations of humidity and the
accumulated pollution. This technique allows continuously
registering the different waveforms of the leakage current
(basic and peak current, magnitude, etc.), until flashover.
Harmonic analysis shows that the main components of
the leakage current are the 60 Hz fundamental and the third
harmonic. There are smaller amounts of the fifth, seventh
and ninth harmonics. Based on these results, the
measurement bandwidth was fixed at 1 kHz. On the other
side, the system revised during 2.5 ms in the ascending
rectified sinusoidal waveform the amplitude to detect a peak
and takes 2 ms to restart the counter peak; moreover, every
semi-cycle of the leakage current is measured [30]. Peak
values were analysed in different levels during the test. As
wetting of the pollution layer increases, higher peak values
and peak numbers are registered.