Oil-paper Insulation Characteristic and Maintenance Measures of Oil-immersed Transformer in Cold Environment

This paper highlights the operating performance of oil-immersed transformer in extreme cold environment along with the researches on the moisture variations in oil-paper insulation system and its effects on transformer caused by ambient temperature. As one of the main factors that affect the electric strength of oil-paper insulation, the effects of moisture on electric strength for oil and oil immersed paperboard are experimental studied, as well as the researches of moisture transfer rule between oil and paperboard caused by the variation in temperature. The experimental results showed that along with the decreasing of operating temperature, the electric strength of oil-paper insulation reduces first and then increase, with an extreme value occurs at the temperature between −10 °C and −0 °C and so as to the low temperature breakdown characteristics or partial discharge (PD) inception voltage characteristics is generally changing as a U-shaped curve. Moreover, the water solubility in transformer oil decreases and the precipitated water unevenly distributed in transformer oil which lead to the dispensability of insulation strength. After the investigating on the problem may appear while transformer operating in an extreme cold environment, maintenance measures are proposed aim to method of cold start, and avoiding oil spills, oil plug, stop of moving components at low temperature.