Transformer Practical Applications

Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to gigawatt units used to interconnect large portions of national power grids, all operating with the same basic principles and with many similarities in their parts.

A rough classification of transformers by the power handled in the circuit, in watts (or, more accurately, VA (volt amperes)):

Up to 1 watt: Signal transformers, interstage coupling 1 - 1000 watts: Small power transformers, filament transformers, audio output transformers 1 kilowatt - 1 megawatt: Power transformers; larger units in this range may be oil filled 1 megawatt and over: Large power transformers, used for substations, large electrical consumers, and for power plants and transmission. Transformers can be classified into various types according to the ratio of the numbers of turns in the coils, as well as whether or not the primary and secondary are isolated:

Step-up the secondary has more turns than the primary Step-down the secondary has fewer turns than the primary Isolating intended to transform from one voltage to the same voltage. The two coils have approximately equal numbers of turns, although often there is a slight difference in the number of turns, in order to compensate for losses (otherwise the output voltage would be a little less than, rather than the same as, the input voltage). Variable the primary and secondary have an adjustable number of turns which can be selected without reconnecting the transformer. The transformer may be an autotransformer used for regulation or adjustability. For example, a typical Variac (TM) can transform 120 volts to an adjustable voltage that ranges from zero to 140 volts is an autoransformer with a sliding tap on the winding to allow adjustment. In all cases the primary winding, or the secondary winding, or both, may have taps that allow selection of one of several different ratios of primary to secondary turns. A transformer with a single winding where part serves as both primary and secondary is known as an autotransformer.