Key Differences Summarized
3. Voltage Levels
The most significant difference is voltage. Transmission substations deal with extremely high voltages, often hundreds of kV, to minimize losses over long distances. Distribution substations, on the other hand, handle much lower voltages, typically in the kV range, suitable for direct use by consumers. This voltage transformation is crucial for safety and efficiency.
Think of it like this: you wouldn't try to drink water directly from a fire hose. The pressure is way too high! Similarly, you can't plug your phone charger directly into a high-voltage transmission line. The voltage needs to be "stepped down" to a usable level, which is exactly what distribution substations do.
Voltage difference is also the critical differentiator between different types of substation equipment. For example, the insulations and clearances are much smaller for the Distribution Substations relative to the Transmission Substations. This has implications for the space required for each of these Substations.
This difference in voltage also necessitates a different type of worker/ engineer and their skill level, for designing and maintaining the different types of substations.
4. Location, Location, Location
Transmission substations are strategically located near power plants or at key points along the transmission network to facilitate efficient power transfer over long distances. Distribution substations are positioned closer to population centers and industrial areas, where they can deliver power directly to homes and businesses.
Imagine the power grid as a road network. Transmission substations are like major highway interchanges, connecting different sections of the highway. Distribution substations are like the off-ramps that lead to individual towns and cities, providing access to local roads.
Another reason why distribution substations are closer to areas with high population density, is to minimise the voltage drop on the lines, as the lower voltages suffer from higher losses as power moves through the distribution lines.
Its important to also consider the geographical placement. Transmission substations are usually built outside cities as it requires a larger area. On the other hand Distribution Substations can be inside or on the outskirts of cities.
5. Purpose and Function
The primary purpose of a transmission substation is to efficiently transmit large quantities of power over long distances. The main job of a distribution substation is to step down the high voltage transmission into lower voltage levels that is used in various residential and commercial buildings.
If transmission substations are highways, distribution substations are more like local roads. One makes long journeys easy, other makes the end user of the journey possible.
The purpose of these substations directly influences the equipment that is installed on them. Transmission substations often contain large circuit breakers that disconnect sections of the power grid during a short circuit/ fault on the network. Whereas, distribution substations include fuses that offer similar protection at a smaller and more local level. The protection schemes are usually layered, where, if a downstream protection does not operate, the upstream protection operates.
The function of a substation has a direct impact on its design. If a particular substation has a function of injecting reactive power into the network in order to increase the voltage locally, then Static VAR Compensators are installed there.
