Field-Filter Probes and the Measurement of Alternating-Current Corona

The principles of the field-filter probe, which is capable of measuring both field changes and conduction current at an electrode in the presence of space charge, are described. Design characteristics are given for a simple field filter and for two further types which can be used for bipolar (reversing) fields and currents. Measurements are given for the discharge characteristics at the plane electrode of rod-plane gaps in the range 50-300 mm subjected to alternating voltages up to 100 kV root mean square (rms).