What is the primary use of a transformer in electrical systems?

The primary use of a transformer in electrical systems is to step up or step down voltage. This functionality is essential in power distribution, where electricity needs to be transmitted over long distances at higher voltages to reduce energy loss. By increasing the voltage, transformers allow for efficient transportation of electrical energy through transmission lines. When the electricity reaches its destination, transformers can then reduce the voltage to a safer, usable level for homes and businesses.

This capability to adjust voltage levels is crucial because it enables the optimization of electrical systems for both efficiency and safety. Other options like increasing current or converting AC to DC do not accurately represent a transformer's role. A transformer does not store electrical energy either; it simply facilitates the transfer and transformation of voltage levels in an electrical circuit. Thus, the correct answer highlights the primary operational feature of transformers in electrical systems.