Substations are among the components of an electrical power system that plays a very important role in the transmission and distribution of electricity from generating power plants or sources, to the consumer’s load. It serves as an intermediary point between the source and load distribution networks. The main functions of these stations include voltage transformation, switching, and protection of the electrical circuits and thus manage the flow of electricity safely with reliability and efficiency. They are essential for ensuring the reliable delivery of electricity while maintaining grid stability and managing power quality.
Table of Contents
What does it look like?
Types of Substations
Classification based on insulation:
Air-insulated switchgear substation:
An air-insulated switchgear ss (AIS) is a type of electrical substation where the major components such as circuit breakers, busbars, disconnect switches, and other equipment are exposed to the surrounding air. It is a traditional and widely used design for the ss, particularly in areas where land is abundant and environmental considerations allow for open-air installations. They are often preferred for medium to high-voltage applications in urban and rural areas where cost-effectiveness and ease of maintenance are top priorities.
Gas-insulated switchgear substation:
A gas-insulated switchgear ss (GIS) is a type of electrical station in which the major components are assembled inside a sealed enclosure filled with gas, mainly sulfur hexafluoride (SF6).
Classification based on voltage levels:
Generating substation:
A generating station is also known as a power plant station which is a critical component in the infrastructure of a power generation facility. It serves as the interface between the electricity generated in the power plant and the transmission network, which transmits or evacuates the bulk power generated over long distances. The incommer is usually between 11KV and 33KV (HIGH VOLTAGE). The voltage is usually stepped up to higher voltages of 110KV and above for transmitting to long distances.
Transmission substation:
A transmission ss or a grid ss is a key part of the electrical grid that plays a crucial role in transmitting high-voltage electricity from generating stations to distribution stations and large industrial consumers. Incomer is usually between 66KV to 765KV (EXTRA HIGH VOLTAGE). Here the voltage is usually stepped down for further transmission to medium-distance or low-distance distribution points.
Primary Distribution substation:
A distribution station is a vital component of the electrical power system responsible for distributing electricity from extra-high-voltage transmission lines to lower-voltage distribution lines that serve secondary distribution stations, and commercial, and industrial consumers. The incomer is usually 33KV. The voltage here is stepped down usually to 11KV for further transmission to low-distance areas or load centers.
Secondary Distribution substations:
These are generally pole-mounted. Voltage ranges from 11 KV and lower. They serve residential and commercial consumers. Voltage is usually stepped down to 415 volts for use in domestic and commercial loads.
Classification based on function
Step-up substations:
A step-up SS is a crucial part of the electrical power grid that facilitates the transformation of electrical voltage from a lower level (typically generated by power plants 11KV to 15KV) to a higher level (132KV/220KV/400KV…) suitable for transmission over long distances. It uses a step up Transformer.
Step-down substations:
A step-down unit is a crucial component within the electrical power grid, serving to reduce the high voltage of electricity received from transmission lines to lower, safer levels suitable for distribution to residential, commercial, and industrial consumers. This transformation is vital for ensuring that electricity can be efficiently and safely utilized by end-users without compromising the integrity of the grid. Step down Transformer is taken into service here.
Classification based on service rendered:
Transformer substation:
Premises which has a transformer installed for the transformation of required voltages.
Switching substation:
Here only the switching of lines is done. No voltage alteration is done in this type. It usually has no Transformers.
Converting substation:
In this type, AC power is converted to DC power and vice-versa.
COMPONENTS OF A SUBSTATION
Transformer:
It is the most costly equipment in the premises. It functions to step up or down the level of voltage in electrically disconnected, magnetically coupled circuits.
Surge Arrester / Lightning Arrester:
This is basically the 1st line of defense of any substation as it protects the equipment from lightning and voltage surges. LA / SA is the 1st equipment in a bay and so it is also called 1st line of defence. Lightening arresters are always connected in electrically parallel connections.
Circuit Breaker
Circuit breakers are basically switching devices that, in conjunction with various protective relays, protect a circuit from various electrical faults by quick disconnection of the circuit. High voltage circuits produce a large amount of arc upon disconnection, the circuit breaker’s interrupter facilitates quick quenching of this arc upon disruption of the circuit.
Instrument Transformer:
The Instrument Transformers are used to lower the values of electrical parameters for metering and protection purposes. The meters are not rated to the high voltages because of cost and the increased use of insulation will add to the bulkiness of the design. The protection system relays are also rated to minimal voltage and current compared to that in the circuit. So to bring the actual values down, current transformers and potential transformers are used.
Disconnector switch or Isolators:
These are used for ease of maintenance in the circuit breakers and necessary feeders/lines. Most line isolators consist of an Earth switch or ground switch which is used to ground the line for safe maintenance activities.
Bus
The bus is basically composed of conductors for three phases. It runs perpendicular to the lines. The bus is the point that collects and distributes all power from lines to different feeder bays. Various Bus schemes used commonly are single bus schemes, double main and transfer bus schemes, one and half breaker schemes, etc.
