High frequency tests at frequencies varying from several kHz are important where there is a possibility of high
voltage in the lines etc., and in insulators which are expected to carry high frequency such as radio transmitting
stations. Also in the case of porcelain insulators, breakdown or flashover occurs in most cases as a result of high
frequency disturbances in the line, these being due to either switching operations or external causes. It is also
found that high frequency oscillations cause failure of insulation at a comparatively low voltage due to high
dielectric loss and heating.