The main function of a capacitor in electrical power systems is:

The primary role of a capacitor in electrical power systems is to control the flow of reactive power. Reactive power is essential in AC systems, as it is used to maintain voltage levels necessary for the proper functioning of electrical equipment. Capacitors help manage and balance this reactive power, which is particularly important in systems where inductive loads, such as motors and transformers, are prevalent.

When these inductive loads operate, they consume reactive power, which can lead to voltage drops and reduced system efficiency. By installing capacitors in the system, reactive power is supplied, improving the overall power factor, enhancing voltage stability, and reducing losses in the power distribution network. This active contribution helps ensure that the available power is effectively utilized, maintaining the health and performance of the electrical grid.

While other options mention filtering noise or grounding, which have their own importance in specific contexts, they do not encapsulate the core function of capacitors within the broader scope of managing reactive power in electrical power systems. Increasing current levels, as implied by another option, does not accurately describe a capacitor's role, since the purpose of a capacitor is more aligned with voltage control and reactive power management rather than increasing current.