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| Effect of Temperature on Moisture Migration and Partial Discharge at the Oil-Paper Interface |
| Liu Yunpeng1,2, Yang Chaojie1,2, Zhao Tao1,2, Yang Jiajun1,2, Liu Yijin1,2 |
1. Hebei Provincial Key Laboratory of Power Transmission Equipment Security Defense North China Electric Power University Baoding 071003 China;
2. State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing 102206 China |
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Abstract The increase and decrease of internal temperature in transformers can cause changes in the distribution and accumulation of moisture in the oil-paper insulation, and high moisture content can seriously affect the electrical strength of the oil-paper insulation. Previous simulations and tests were conducted at temperatures not exceeding 80℃ and without bubble interference. Few scholars have raised the temperature to the initial temperature bubble effect to study the moisture migration and partial discharge (PD) characteristics under extreme temperature conditions. Therefore, it is necessary to study the effects of temperature changes during the heating, bubbling and cooling phases on the moisture migration and PD at the oil-paper insulation interface.
In this study, using wedge-plate electrodes, the PD characteristics of oil-paper insulation systems with different moisture content (WC = 3.61% and WC = 5.76%) were investigated under transient moisture conditions during the processes of heating, bubbling, and cooling. During the temperature change process, the temperature, moisture concentration, and moisture activity of the oil were continuously monitored, and PD tests were conducted using the voltage rise and constant voltage methods. For the voltage rise, the voltage was increased at a rate of 1 kV/(10 s) and the partial discharge inception voltage (PDIV) was measured by this method to determine the PD charge threshold for the first PD event as 100 pC. If the applied voltage reached the PDIV, it was immediately recorded and the voltage was reduced. The rest of the tests were performed at a constant voltage. All tests were performed in an electromagnetically shielded room to avoid interference with PD measurements from external activities.
The experimental results showed that as the temperature increased, the PDIV at the oil-paper interface briefly increased, followed by a gradual decrease in PDIV and a sudden increase in PD intensity. The moisture content in the oil gradually increased in both systems. The higher the moisture content in the oil-immersed paperboard was, the more moisture entered the oil. Bubbles appeared, PDIV rapidly decreased, and the moisture content in the oil sharply increased. During the cooling stage, PDIV in both systems showed a decreasing-then-increasing trend, and correspondingly, PD intensity showed an increasing-then-decreasing trend, maintaining a relatively high level. Even when the oil temperature dropped to room temperature, PD did not completely disappear. The research findings have important theoretical value for the real-time monitoring of moisture in oil-immersed electrical equipment and the evaluation of its insulation performance.
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Received: 27 September 2023
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2024, Vol. 39 
