Substations play a crucial role in:

The correct answer is: a) Stepping up or down voltage levels.

Substations are electrical facilities that connect two or more transmission lines. They are used to step up or down voltage levels, as well as to switch and protect power lines.

Substations are an essential part of the electric power grid. They help to ensure that electricity is delivered safely and reliably to homes and businesses.

Here is a brief explanation of each option:

• Option a: Stepping up or down voltage levels. Substations use transformers to step up or down voltage levels. This is necessary to transmit electricity over long distances.
• Option b: Converting AC to DC power. This is not a function of substations. AC power is the type of power that is used in homes and businesses. DC power is used in some electronic devices, but it is not transmitted over power lines.
• Option c: Ensuring grid stability. Substations do help to ensure grid stability by switching and protecting power lines. However, this is not their primary function.
• Option d: Monitoring power quality. Substations do not monitor power quality. This is done by other devices, such as power quality meters.