Abstract: Generally, the estimated auxiliary power rate in design stage is greater than its actual value with relative error about 20%, which will influence the economic evaluation for project approval and the long-term economic benefits. Analysis indicates that the error mainly comes from the fact that the same factor K is adopted in the conversion factor method (CFM) for auxiliary power rate estimation and high-voltage auxiliary transformer capacity determination. The load ratio method proposed adopts a specified K_L for auxiliary power rate estimation. The K_L is critical to the new method and its determination is demonstrated through examples. The proposed method has been used in 12 projects. The average relative error is less than 2%, which shows that the estimation accuracy is improved almost by 90% compared to that of CFM.

Key words: power plant design, estimation of auxiliary power rate, load ratio method, conversion factor method