Evaluation of space charge in liquid dielectric using kerr electrooptic method

In dielectric liquids subjected to a high electric field, space charges are generated due to various reasons, for example, by the injection of charges from electrodes or by ionization of the impurities and molecules. It is necessary to obtain information regarding the electric field and space charge distributions in insulating materials to ensure effective insulation, however, it is very difficult to obtain information regarding space charge in liquid. We have investigated the electric field distributions in liquid dielectrics using the Kerr elctrooptic effect. Recently, the electric field distribution in the order of milli-seconds has been able to be measured. For 1 ms immediately after an applied voltage, it is thought that space charge layer is almost never formed. So, we measured the electric field distribution for 1ms at the applied voltage. Then, after a period of time, we measured again the electric field distribution at the second application of the voltage pulse. If there is a difference between the two, it is considered that it is caused by remnant electric charges. So, we report on the evaluation of the remnant charge in liquid.