The information in this chapter is on the construction, theory, operation, and the various uses of transformers. Safety precautions to be observed by a person working with transformers are also discussed.
A transformer is a device that transfers electrical energy from one circuit to another by electromagnetic induction (transformer action). The electrical energy is always transferred without a change in frequency, but may involve changes in magnitudes of voltage and current. Because a transformer works on the principle of electromagnetic induction, it must be used with an input source voltage that varies in amplitude.
When AC is used, the voltage and current levels can be increased or decreased by means of a transformer.
As you know, the amount of power used by the load of an electrical circuit is equal to the current in the load times the voltage across the load, or P = VI. For example, if the load in an electrical circuit requires an input of 2 amperes at 10 volts (20 watts) and the source is capable of delivering only 1 ampere at 20 volts, the circuit could not normally be used with this particular source. However, if a transformer is connected between the source and the load, the voltage can be decreased (stepped down) to 10 volts and the current increased (stepped up) to 2 amperes. Notice in the above case that the power remains the same. That is, 20 volts times 1 ampere equals the same power as 10 volts times 2 amperes.