This paper proposes a method of distinguishing the contributions of ionized and injected charges to the charge transport in oil immersed paper in triple-layer and double-layer samples. With the double-layer sample, the apparent mobility including the ions contribution is obtained by the calculation according to the speed of accumulated charge density at the interface. The contribution of ions is excluded by subtracting the accumulated charge density in the triple-layer sample from that in the

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... uble-layer sample. It is found that the interface charge mainly comes from the ionization charges under a low field, and the contribution of injected charge takes a more important part at higher electric field. Index Terms -ionization, space charge, interface charge, carrier mobility correction, oil immersed paper material, pulsed electroacoustic (PEA) method Yang Wu was born in Shandong, China, in 1992. He received the B.S. degree in electric engineering from Xi'an Jiaotong University, Xi'an, in 2015. Currently, he is a Ph.D. student in the Department of Electrical Engineering at Xi'an Jiaotong University. His research interests are in space charge properties and simulation of space charge in HVDC equipment.