Determination of the Dielectric Characteristics of Electric Equipment Insulation in the Presence of Utility-Frequency Interference Currents

The operation of modern microprocessor insulation analyzers operating at the utility frequency and implementing the two measurements method (computational method) which are widely used to assess the condition of insulation in electric equipment is analyzed. The expressions and computational results are presented for the errors appearing in tanä due to the voltage setting difference between the first and second measurements and the action of the utility-frequency interference currents on the source of the testing voltage. It is shown that the two measurements method gives acceptable errors if the voltage difference between the first and second measurements does not exceed 0.2 – 0.5%. It is noted that the level of the additional errors of the insulation analyzers using the two measurements method is comparable to the error of simple analyzers of the type Tangens-2000 operating on a non-utility frequency and having significant additional errors in the presence of utility-frequency interference currents in the distribution devices.