Electrical substations are basically the interface that lies between transmission and distribution systems. These are designed to reduce voltage in transmission lines to levels that distribution systems can withstand. In-built circuit breakers protect the distribution system and also manage the current flow in different directions. These also manage fluctuations in voltage to manage heavy loads.
All in all an electrical substation comprises of the following components:
- Lighting arresters
- Instrument transformers
- Electrical power transformers
- Circuit breakers
- Bus bars
- Capacitor banks
Types of Substations
Different types of substations have their own voltage class, their use in a power system, insulated connections and the material used in their construction. Here are some common substations that exist in a system:
- Transmission Substation. As the name implies, this type of substation is used to join 2 or more transmission lines which have the same voltage running through them. That is why this substation also has high voltage switches to aid personnel in clearing faults safely. A transmission substation usually has transformers between the voltages, capacitors, reactors and other equipment that can manage power flow between systems easily. These can also be simple or complex depending on the voltage level. For instance, a transmission substation may just need a bus and some circuit breakers to work. Complex ones may require larger areas and a number of voltage levels, circuit breakers and protection to work. The equipment it might need can range from SCADA systems and relays to voltage and current transformers.
- Distribution substation. As the name implies a distribution substation transfers power from the transmission system to the distribution system of any given area. This saves power plants a lot of money since it can be quite costly to connect electricity consumers to the main network. It requires massive amounts of power which can also be hazardous. An economical and safer alternative is to allow distribution systems to reduce voltage intensity into levels that can be distributed on a local level easily. Usually, a distribution substation gets at least two transmission lines and the output is usually through a number of feeders. The voltage levels are usually medium according to the area served and how it is used. The feeders are usually based underground or along streets and the distribution transformers are usually near homes and offices of consumers. Besides transforming voltage, these substations also isolate faults in distribution as well as transmission systems. They also regulate voltage levels on distribution circuits that are several miles long. This system can also be installed along the entire line to ensure voltage levels remain in control. Large cities may have several complex distribution substations complete with voltage-heavy switching and strong backup systems. In smaller areas, this system may only be made up of a single transformer and very few facilities to control voltage.
- Converter Substations. These substations are usually associated with traction current and HVDC converter plants. Converter substations comprise of powerful devices that can alter the frequency of the current running through the system. Converter substations are also used to convert alternate current to direct current and vice versa depending on need.
Structure of an Electrical Substation
Most substations which are located above ground have some things in common in their construction. These usually include wooden poles, a metal tower featuring latticework and tube based metal structures. Substations that are based on larger areas are usually supported by steel lattice towers which are low cost.
However, smaller substations are located in suburbs where their physical appearance is given preference. Substations that are based indoors are either gas insulated or covered in metal for low voltages. However, whether these are located in urban or suburban areas, substations are designed to blend in with surrounding buildings.
The smallest substation is a compact substation. This is usually based outside and enclosed in a metal cage. Each component is located side by side to save as much space as possible.