On the relationship between current pulses and discharges

Current instabilities in the farm of randomly occurring pulses are a problem encountered by all who endeavour to produce current-voltage characteristics of a liquid insulant. These pulses signal the impending electrical breakdown of the system unless precautions are taken. In addition to an intensive cleaning of the system and filtration of the liquid entering the test cell the usual procedure is stress conditioning of the system whereby the voltage is held at a constant value for a long period until pulse activity has reduced, thus allowing the voltage to be raised a little and the whale process to be repeated. This technique has allowed current measurements at high values of electric stress. Figure 1 illustrates a typical plot obtained in this manner using a plane-plane electrode configuration in hexane. The original onset of the pulse activity is indicated on the graph. A similar characteristic is obtained if the plane cathode is replaced by a point cathode. This is shown in figure 2. Although the current magnitudes are greater with a point cathode the onset of the current pulses is seen to occur at the same relative part of the curve.