Review on the characteristic of new cellulose insulation paper used in the converter transformer

Converter transformer is one of the most critical and strategic components in HVDC transmission, and its insulation system of the valve-side winding generally has high failure rate because of complex operation conditions. Although the traditional methods can improve the equipment reliability through on-line monitoring and fault diagnosis techniques, yet it is hard to guarantee the efficiency and economy when the maintenance cost and power transmission loss cost during the outages are taken into account. As the major insulation system in the valve-side winding, oil-paper insulation plays a vital role in the reliability and safety of converter transformer. Wherein, the insulation paper of the insulation system is not only deteriorated by the long-term impact of thermal stress, but also subjected to complex operating conditions such as AC-DC hybrid voltage and polarity reversal. Besides, the insulation paper is considered to be irreversible after degradation. Therefore, it is essential to improve the performance of insulation paper. This paper overviews the overseas and domestic research status combined with the studies of our group, aiming at improving the anti-thermal aging performance, breakdown performance and space charge characteristics of cellulose insulation paper. All the mentioned methods will be analyzed in this paper, and a new cellulose insulation paper used in the converter transformer is investigated. © 2016, The editorial office of Transaction of China Electrotechnical Society. All right reserved.