ABSTRACT
The leakage impedance of a transformer is one of the most important specifications that have significant impact on its overall design. The material cost of the transformer changes when the specified impedance value is changed. The cost is minimum for a particular value of the impedance when all other specified performance figures are held constant. The leakage reactance is then calculated from the impedance and the resistance. Since the resistance is much lower than the reactance in transformers, the latter is almost equal to the leakage impedance. The percentage impedance, which is specified by transformer users, can be as low as 2% for small distribution transformers and as high as 20% for large power transformers. Impedance values outside this range are specified for special applications. The individual leakage reactance of a winding can be negative. Negative impedances are virtual values, and they reproduce faithfully the terminal characteristics of transformers.
