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In this Paper the polarization and depolarization behavior of oil impregnated paper by a DC voltage and its influence on the breakdown voltage by reversed polarity is presented.As Power transformers for HVDC applications are tested with a polarity reversal test before commissioning the insulation system is stressed with AC and DC fields. The behavior of the insulation system under this DC stress is not jet adequately investigated. To get a further understanding of the charge movement by applying a DC voltage polarization and depolarization current of oil impregnated paper insulation is measured. Furthermore the influence of a polarization of this insulation to the electrical performance by polarity reversal is investigated.