An optimum ratio of copper losses and iron losses for a transformer with variable load

When a power transformer is loaded so that it is operating at maximum efficiency the copper losses are equal to the iron losses The `efficiency¿ is, of course, the `power efficiency¿, i.e. the ratio of output power to input power. The same condition applies for maximum `energy efficiency¿ only if the load is constant for the period being considered. With most transformers the load varies considerably over a load cycle and the optimum ratio of copper losses to iron losses calculated on the assumption of constant load for a given period can only be, at least, a rough approximation. The paper suggests a method of obtaining a more accurate optimum ratio in cases where the load variation of the transformer can be estimated in advance. The assumption is made that the copper resistance is constant.