Effect of AC Voltage and Frequency on Insulation Characteristics of Transformer Oil Containing Cellulose Particles
Liu Yunpeng1,2, Zhao Jiaying1, Liu Hechen1,2, Zhao Tao1, Yin Ziao1
1. Hebei Key Laboratory of Green and Efficient New Electrical Materials and Equipment 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
Abstract：Low-frequency transformer is the key equipment in low-frequency transmission system, the insulation characteristics under low-frequency voltage have important meaning for its design and operation. In this paper, so as to study the insulation characteristics of transformer oil containing cellulose particles under low-frequency voltage, transformer oil breakdown tests at different cellulose particle size (low, medium and high) levels under AC voltages of 20Hz, 30Hz, 40Hz and 50Hz were conducted. In this paper, the test frequency was selected as 20Hz, 30Hz, 40Hz and 50Hz, and the content of cellulose particles in oil samples was selected as low, medium and high particle size levels. According to IEC60156 standard, the pressure was increased step by step at a constant rate of 2kV/s to the oil sample breakdown, and the oil sample in the oil cup was replaced every 6 times after breakdown. In order to ensure the consistency of the test, 30 times of breakdown tests were repeated respectively at each frequency and particle size level, and the effective value of breakdown voltage was recorded. Weibull distribution method was used to analyze the test results. The test results show that at the low particle size level, the breakdown voltage at 50Hz is taken as the reference, and the breakdown voltage at 20Hz, 30Hz and 40Hz is increased by 12.25%, 25.62% and 39.14%, respectively. At the high particle level, the breakdown voltage increases 21.45%, 83.69% and 97.30% at 20Hz, 30Hz and 40Hz, respectively. At the same time, the accumulation process of cellulose particles at the electrode was observed by experiments, and the movement of cellulose particles in transformer oil at different frequencies was analyzed by multi-physical field simulation. In this paper, an observation test was carried out on the motion characteristics of cellulose particles for transformer oil with high particle size level. 18kV was selected as the test voltage and carried out at room temperature. The distribution state of cellulose particles between electrodes was observed with a camera. Finally, COMSOL finite element software "AC-DC module" and "Particle tracking module" are used to simulate the motion trajectory of particles in the slightly uneven field of transformer oil under four frequencies. The results showed that the agglomeration rate of particles towards the electrode at low frequency 20Hz was significantly lower than that at power frequency 50Hz, and more impurities would accumulate near the electrode at 50Hz, and the bridge of impurities was wider than that at 20Hz. The results show that the AC voltage frequency has a significant effect on the bridge formation characteristics and breakdown voltage of cellulose particles in transformer oil. When the transformer is running, the breakdown voltage of transformer oil increases with the decrease of AC voltage frequency, and the higher the granularity level, the more significant the difference of breakdown voltage between frequencies. The frequency of AC voltage will affect the moving speed of impurity particles and the formation process of impurity Bridges in transformer oil. The research results of this paper provide basic data support for the design, operation and maintenance of low-frequency transformer.
刘云鹏, 赵家莹, 刘贺晨, 赵涛, 尹子澳. 低频电压下含纤维素颗粒变压器油绝缘特性及影响因素研究[J]. 电工技术学报, 0, (): 118-118.
Liu Yunpeng, Zhao Jiaying, Liu Hechen, Zhao Tao, Yin Ziao. Effect of AC Voltage and Frequency on Insulation Characteristics of Transformer Oil Containing Cellulose Particles. Transactions of China Electrotechnical Society, 0, (): 118-118.
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