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《Power System Technology》 2008-03
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Insulation Level and Test Technology of 1000kV Power Transformers

LI Guang-fan,WANG Xiao-ning,LI Peng,SUN Lin,LI Bo,LI Jin-zhong (China Electric Power Research Institute,Haidian District,Beijing 100192,China)  
The insulation coordination for the first 1000 kV power transmission project in China is studied and decided under the optimization principle, it is not a simply extrapolation of that for 500 kV power transmission system and is nor completely in accordance with the standards of GB311.1-1997 and IEC60071-1-1993. The insulation level of 1000 kV power transformer adheres to following items: the lightning impulse withstand voltage is 2250kV; the switching impulse withstand voltage is 1800 kV; and the power frequency withstand voltage is 1100 kV/5min. Due to the differences among the insulation levels and insulation test voltages for different windings of UHV power transformer and the close electromagnetic coupling among the windings of UHV power transformer, the power frequency and impulse test voltages are transmitted among these windings by the transformer ratio, thus it is bound to bring about the condition that the insulation design for some conductor terminals can not be checked by the test voltage specified in the technical specification. Besides, due to the high voltage class, high capacity and super size of UHV power transformer, the size of its test circuit is correspondingly enlarged, the impacts of stray inductance and capacitance will be more intense consequentially, thus it makes the front time of voltage waveform in lighting impulse test elongated, however, the design and calculation are generally conducted according to standard waveform, thus in the isolation design of UHV power transformer the attention should be paid to the impact of long front time test voltage. In this paper, the structural features and insulation level of power transformer for 1000 kV power transmission project in China as well as special problems during the insulation test are presented in detail.
【CateGory Index】: TM855;TM41
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