Measurement Techniques for Identifying Polarity Dependence of Ion Injection in Transformer Oil

Paper in proceeding, 2013

Charge injection from metallic surfaces into mineral oil is investigated utilizing transient currents recorded in coaxial cylindrical electrode systems with different degrees of inhomogeneity of electric fields. The currents obtained with single polarity and reverse polarity methods demonstrate differences in their behavior depending on the geometry and type of the test voltage. The data show clear relation between the sign of the current and the polarity of the applied voltage, which is attributed to the polarity dependence of the ion injection from oil-metal interfaces. The results of the experiments are discussed in terms of relaxation time of the system and time of flight (drift time) of ions in the oil gap.