A new method for carrier mobility measurement in oil immersed cellulose paper insulation

This paper reports on a new method to measure the mobilities of both positive and negative charges in insulating materials based on space charge measurement in two-layer samples. To fulfill the condition of a unipolar carrier system, a blocking material is used as a barrier on one electrode thereby preventing charge injection to ensure the unipolar charges injected from the other electrode are transported through the bulk and accumulate at the barrier. Experimentally, the carrier mobility of oil immersed cellulose paper was obtained using the proposed method, and the result of mobilities of both positive and negative charges is presented. The temperature and field dependence of carrier mobility were also investigated, and the activation energies for negative and positive charges were calculated. The obtained carrier mobility of negative charges (majority electron carriers) is approximately 2 times of that of positive charges, and the charge migration can be interpreted by the thermally activated hopping conduction mechanism.