Methods of measuring radio interference from high-voltage insulators

A critical study of the methods available for the measurement of radio interference from high-voltage insulators has been made by comparing the results obtained with the various methods for a range of insulators. It was found that the method which measured the noise current through a resistor coupled to the high-voltage system by a capacitor gave consistent results for all insulators. The second method, which measures the noise currents in the earth lead of the insulator, gave results which depended upon the size of the insulators. This method was subsequently modified by using an artificial earth plane connected to the measuring set. The results then approached those of the first method. A third method assumes that the onset voltage of visual corona is the criterion for the onset of radio interference. It was found that some radio interference was generated before visual corona commenced and that the levels at the critical visual corona voltages depended upon the types of insulators used.