What is a Transformer?
A transformer is an electrical device which converts alternating current from one voltage to another. it can be designed to "step-up" or "step-down" voltages and works on the magnetic induction principle. A transformer has no moving parts and is a completely static solid state device which insures, under normal operating conditions, a long and trouble-free life. A transformer consists of two or more coils of insulated wire wound on a laminated steel core. When voltage is introduced into one coil (called the primary), it magnetizes the iron core. As a result, a voltage is induced into the secondary, or output coil. The change of voltage (voltage ratio) between the primary and secondary depends on the turns ratio of the two coils.
What does a transformer do?
Principle of Operation
A transformer operates on the principle of magnetic induction. Each transformer consists of two or more coils of insulated conductor (wire) wound on a laminated steel core. When a voltage is supplied to the PRIMARY (input) coil, it magnetizes the steel core, which in turn induces a voltage on the SECONDARY (output) coil. The voltage induced from the primary to the secondary coils is directly proportional to the turns ratio between the two coils. (See Fig. 1)
For example, if a transformer's input, or primary leg has twice as many turns of wire as the secondary, then the ratio would be 2:1. Therefore, if you applied 480 volts to the primary, 240 volts would be induced in the secondary. This is an example of a two winding "step-down" transformer. (See Fig. 2) If the voltage is to be "stepped-up" or increased, the same transformer could be turned around and connected so that the input side would have the 240 volts and the output would be 480 volts. (See Fig. 3)
Standard transformers rated at 3kVA and larger can be used for either step-up or step-down service. Transformers rated 2kVA and below have compensated windings and should not be used in reverse feed applications. (Note: some system design considerations apply.)