PROPERLY-DESIGNED transformers are highly efficient (up 99.5% for 500MVA transformers) devices that are chiefly used to step down (or step up) alternating voltages and also for matching loads. They range in size from multi-tonne, multi-MVA transformers in electricity distribution systems to 1VA, PCB-mounted transformers for portable instruments. Besides their high efficiencies, they are also notable for their reliability and freedom from the need for maintenance — virtues stemming from their lack of moving parts. AC became standard partly because transformers have these attractive properties, relegating DC to special purposes.
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