Step Response Measurement of Insulating Liquids and Their Reproducibility

The step response measurement for the determination of the DC conductivity of insulating liquids or, in general, of insulating materials which are exposed to DC voltage in its application is becoming increasingly important. The reason for this is that the conductivity in the case of DC voltage imposition is the decisive variable for the field distribution within the insulating medium. Only with exact knowledge of the temporal course and the stationary final conductivity value it is possible to protect the equipment against overloading in the short and long term and to guarantee an economic design of the insulation system. Measuring micro currents to determine the DC conductivity is a particular challenge. These include special design criteria, reduction of parasitic influencing factors and the desire for reproducible measurements. This paper presents a test setup which allows a step response measurement in the pA-range with conventional components. In addition, a measuring cell is presented which permits the reproducibility of the DC conductivity of insulating liquids within defined limits.