The Measurement of High-Surge Voltages

With the application of surge tests to high voltage electrical apparatus, the question of the measurement of high-surge voltages has become a subject of prime importance. It is accordingly desired in Part I to show the practical work done in the laboratory at Sharon to calibrate the measuring devices, and in Part II to study the more interesting fundamental relationships that affect the operation and accuracy of these measuring devices. The methods of voltage measurement used are the resistance potentiometer, capacity potentiometer, and sphere gap. The potentiometers serve as dividers of the high-surge voltages for measurement at the cathode-ray oscillograph. The resistance potentiometer is a fundamental standard but requires consideration of its limitations for very rapid phenomena. In cases where these can be compensated for or are negligible, the resistance potentiometer method is very desirable. The capacity potentiometer is a secondary standard which can be calibrated. If corona and oscillations can be eliminated, it is a very desirable method of measurement, inasmuch as it is less subject to distorting the wave shape of the surge. The sphere gap is useful as a secondary standard for occasional check measurements, and it is of interest that formulas derived from smaller gaps still hold, as indicated by the check between the calculated curve for the 200-cm sphere gap and the calibration points with the resistance potentiometer.