Transformer model for application in load-flow analysis

This paper gives a closed formula which expresses the variation of the leakage reactance of transformers as a function of the transformer tap position. The derivation of the formula is based on the analysis of the distortion of the leakage field as portions of the winding are cut out by means of tappings. Three cases are examined, depending on whether taps are cut out: - asymmetrically at the end of a winding, - at the electrical centre of a winding or - symmetrically at the end of a winding. The validity of the derived model is rested by comparison with existing transformer impedance correction data. Finally test results from the incorporation of the model in a load-flow program ave presented.