Are manufacturers published transformer efficiency claims, under nonlinear load conditions, legitimate?
A number of manufacturers now claim transformer efficiencies that meet or exceed the requirements of NEMA TP 1-2002, under severe nonlinear load conditions. One manufacturer has even published their test methods. At best, these claims are misleading since: a) There is no recognized standard guide for determining the energy efficiency of distribution transformers or a standard test method for measuring their energy consumption, b) The manufacturers that make these efficiency claims are basing them on the Power In Power Out Measurement Method. Based on the manufacturers published test method, which utilizes +/-0.3% revenue class instrumentation accuracy, the measurement error will be +/-1.5%, when measuring the efficiency of a transformer. As a result, a claimed efficiency of 98%, for a 75kVA transformer, may, in fact, be only 96.5%. There are a number of IEEE transactions that confirm that this test method will yield inaccurate results.
