Which of the following describes a substation?

A substation is an integral part of the electricity supply network, primarily responsible for the transformation and regulation of electrical power. It typically contains transformers that step down high-voltage electricity from transmission lines to a lower voltage suitable for distribution to homes and businesses. Additionally, substations are equipped with various switching devices that manage the flow of electricity and ensure the stability and reliability of the power system.

The presence of transformers is essential, as they allow for the efficient transmission of electricity over long distances and help maintain voltage levels within the required limits. Switching equipment is also crucial for routing power, disconnecting faulty sections, and managing load distribution across the grid.

The other options do not capture the full functionality and purpose of a substation. For example, an underground facility that generates electricity refers more to power generation sites rather than substations that distribute and facilitate the power flow. A standalone grid that distributes renewable energy is a description of a microgrid, which operates independently of the larger power grid and is not the function of a typical substation. Meanwhile, a small transformer installed at each home is indicative of distribution transformers, which are different from the larger transformers found in substations.