Space charge behavior in oil-paper insulation under polarity reversed voltage

Converter transformers are suffered from DC voltage, DC voltage with AC voltage and polarity reversed voltage additionally, compared with common power transformers. Under DC voltage it is easy to form space charge in oil-paper insulation. The formation, distribution and mobility of space charge will affect its dielectric performance. What´s more the insulation system is easier to fail under polarity reversed voltage. In order to observe space charge behavior in oil-paper insulation under different polarity reversed conditions, space charge measurement is made under different voltage reversed polarity (from positive to negative and from negative to positive) and different voltage reversed time (20s, 30s, 40s and 60s) separately. The pulsed electro-acoustic (PEA) method is used for space charge measurement at room temperature. The impact of voltage reversed polarity and voltage reversed time on space charge characteristics was discussed. Besides the electric field distortion in samples with different polarity reversed conditions is calculated. The experimental results show that polarity reversed conditions have great effect on space charge characteristics.