Measured Variability of Performance Parameters of Power & Distribution Transformers

This paper presents measured variability between values of performance parameters of three multi-unit orders of power and distribution transformers. The performance parameters studied are no-load loss, exciting current, load loss, impedance, windings temperature rise, and sound level. Factors contributing to the magnitudes of the variability of these different performance parameters are discussed in detail. These factors include material variability, production process variability, and measuring process variability. As demonstrated in the paper, each of these contributes to the variability of the different performance parameters of the transformer in different proportions. Finally, the paper discusses how the results presented can be used to determine the appropriate design margin as well as tolerances to be allowed in industry standards. The results of this work have already been used to arrive at the new tolerances implemented in IEEE C57.12.00 for no load and load losses (Ref. 1)