What device is primarily used to regulate voltage in electrical systems?

The primary device used to regulate voltage in electrical systems is a step regulator. This device is specifically designed to adjust and stabilize voltage levels in electrical distribution systems, ensuring that the voltage delivered remains within a specified range even with varying load conditions. Step regulators are often used in conjunction with transformers to step up or step down voltages as needed, but their main function is to provide fine adjustments to maintain a consistent voltage level.

Other devices mentioned in the question play different roles. For instance, while transformers can change voltage levels, they are not primarily used for regulating voltage, especially under varying load conditions. Capacitors and inductors, on the other hand, mainly deal with reactive power and energy storage; they are not focused on voltage regulation in the same way that step regulators are. Therefore, the function of a step regulator directly aligns with the need for maintaining consistent voltage levels in electrical systems.