Effect of pressure on discharge current harmonics of porcelain insulator specimen

This paper presents some properties of surface discharge currents due to air pressure influence on porcelain insulator specimen. The specimen was subjected by high voltage source in a hermetically sealed chamber, where the pressure could be adjusted and measured simultaneously. The applied voltage and discharge current waves were recorded by a storage digital oscilloscope, transferred and saved to a computer. The discharge current waves were analyzed using FFT. The result indicated that the discharge currents occurred in intermittent conditions. After the fundamental frequencies, the second highest amplitudes were third harmonics. These were different from leakage current as usual, which fifth harmonics were as second highest amplitudes. The discharge current amplitude would increase as the pressure reduced. In other word, the discharge breakdown voltage would increase as the air pressure increase. The discharge currents experienced a suppression on the front of waves. Almost harmonics have negative correlation coefficient to pressure, except THD, that has 0.45 of correlation coefficient to pressure.