Space charge formation in insulating liquids under DC stresses

The occurrence of space charges has to be understood, in order to study the field distortion which is due to space charges. Hence, the investigation of space charge behavior and its origin in insulating liquids is necessary for design of optimal insulation system. It is important to know about the type of charge carriers present in insulating gap. Applying different DC stresses with various polarities can be helpful to determine the thickness of space charge regions near the electrodes and consequently, to achieve knowledge of space charge distribution both in insulating liquid and along the electrode surfaces. If an electrostatic field is applied onto the insulation between two electrodes, the charge carriers will begin to move towards the electrodes and neutralize themselves on metal electrodes. To determine the velocity of charge carriers during the measurements, a polarity reversal test is recommended which can be performed after long-duration conductivity measurements. In this investigation, the polarization current is measured using a plate-shaped test cell with stainless steel electrodes which allows a variation of gap between 1 to 5mm. In this case, the measurement set-up is based on low level current measurement with high sensitive ammeters because the current flowing through an insulation system is some pA's only. Finally, all these input parameters are used to describe the physical phenomena which occur during the conduction process.