No-Load Versus Load Loss: Making Transformer Losses Part of the Purchasing Decision

The theory of transformer losses expressed as no-load loss and load loss is briefly reviewed in this article. Mathematical expressions for per-unit loss as a function of load are developed based on rated and actual load. Present value equations are used to express the cost of losses as a function of transformer characteristics, electricity cost, and discount rate. Three methods are presented for expressing the cost of losses in forms that can be used to evaluate bids.