On-line correction of transformer parameter based on orthogonal least squares

An important step in economical operation analysis for transformers is the calculation of power loss curve. In order to find out the curve which best fits the actual conditions, we need to correct the nameplate ratings of the transformer. Taking the type test is the traditional method. But the result of this not-so-flexible method will become inaccurate with the lapse of time. Fitting the real-time data by using classical least squares (CLS) method is another method, whereas its result lacks accuracy in transformer parameter correction. Aiming at the shortages of above two methods, an on-line correction method based on orthogonal least squares (OLS) method is introduced in this paper. In this method, both time and cost will be saved because we do not need to shutdown the transformer. A significant advantage is that this method is suited for the problem includes observational errors on both dependent and independent variables. This on-line method can be used whenever users want. Taking a double winding transformer in a substation as an example, the result shows that the estimates obtained with the OLS method are more reliable than those with the CLS method and our on-line method is quite flexible and accurate.