A computer based technique is described which can accurately determine high voltage ac resistive currents by obtaining the watts loss of the test specimen and dividing by the true rms (trms) value of the applied voltage. Therefore, the normal concern for guarding out stray capacitive currents, and the exact repetition of test setup geometry on successive testing is not required for accurate measurements of ac resistive current. The watts loss calculation is based on the general formula for average watts so that the resistive current can be measured accurately with some harmonics of the fundamental present in both the test current and the supply voltage. A method of system calibration is presented which allows the use of normal laboratory high voltage dividers. A digital oscilloscope is used to acquire the test voltage and current so that special purpose amplifiers are not required. The overall system accuracy is verified to less than +/- 1.21% of full scale current. A microprocessor is used to compute the following parameters: average power, trms voltage, trms resistive current, trms capacitive current, total trms current, and the magnitude of calculated measurement error. The waveforms displayed are: voltampere, voltage, and total current. An EHV aerial lift boom, a 115kV station post insulator, and a metal-oxide surge arrester are evaluated using the unique ac resistive current technique to illustrate the measurement advantages.
