What is the primary function of a transformer in an electric circuit?

The primary function of a transformer in an electric circuit is to regulate the voltage level. Transformers are designed to either step up (increase) or step down (decrease) voltage levels in AC circuits without altering the frequency. This ability to adjust voltage levels is critical for efficient power transmission over long distances and for ensuring that electrical devices receive the appropriate voltage for their operation.

Using transformers helps to minimize energy losses that occur during transmission, allowing for more efficient distribution of electricity. They work based on the principles of electromagnetic induction, where an alternating current in one coil generates a magnetic field that induces a voltage in another coil.

Although other functions listed in the question are important in the electrical system, they do not represent the primary role of a transformer. For instance, changing the phase of the current or converting AC to DC involves different types of equipment such as phase converters or rectifiers, and storing electric charge pertains to capacitors and batteries rather than transformers.