The Rating or Power Transformers as Determined by the War Emergency

Accurate rating of transformers is one of the most important elements in the problem of providing continuous service to the customers of the utility industry. Rather than attempt to follow a general rule for the loading of transformers it is believed that the urgency of wartime needs amply justifies the effort required to place individual ratings on each transformer bank of the utility under consideration. Experience has shown that such ratings vary widely. The transformers cover a wide range of sizes, designs, manufacturers, and periods of manufacture; with weights per kilovolt-ampere ranging from 7 to 20 pounds, excitation voltages ranging from 95 to 110 per cent, their daily load factors from 25 to 100 per cent, and their seasonal loading from 0 to 100 per cent. The consequent saving of ``critical´´ material is self-evident when each case is considered individually. During the war it is desirable to base station ratings on the thermal capacity of all the transformers normally available for service, rather than attempt to set up station ratings based on abnormally high emergency ratings of the remaining units after the assumed failure of one unit. It is essential that these higher station ratings be properly applied so that the danger of failure is minimized.