Abstract: Taking the frequency conversion reformation of the primary air fan of unit No.14 in Wangting Power plant as example, the design idea of the frequency conversion control system of the primary air fan and the technical points in its concrete realization were introduced. A simple and practical control scheme of variable frequency speed control system for primary air fan of unit No.14, which was designed to suit its features, was provided. In same time, the automatic control scheme of the primary air fan run back (RB) test was perfected. The experiment, which was carried out after the variable frequency speed control system of the primary air fan was put into operation, that the scheme can effectively avoid the MFT protection action due to fault of the air fan frequency converter and can obtain favorable effect of primary air pressure control. 
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Key words: primary air fan, frequency conversion reformation, automatic control strategy, run back (RB) test