A transformer is a passive electrical device that transfer energy between circuits through electromagnetic induction. Current flowing through one coil in the transformer produces a magnetic field, which induces voltage in a second coil.
Induction between coils allows a transformer to increase or decrease voltage, making transformers essential for power transmission, distribution and utilization in AC power applications.
Transformers are most often used to decrease supply voltage for low voltage circuits. They are also used to isolate equipment from mains power, maintain constant voltage, measure voltage potential, and measure current.