Electrical Substation

What is Electrical Substation?

Electrical Substation is an important part of the electrical power system. The substation is an electrical power station where the voltage level is changed by special apparatus (power transformer, and other switchgear equipment) and sent to a different location which is called a substation. Most of the substations in the electrical power system are step down substations whereas the voltage level is changed from upper voltage to lower voltage. Power substation consists of a large number of the component such as

  • Power Transformer
  • Switchgear components(like a relay, circuit breaker, air break switch, isolator, circuit breaker, etc.)
  • Some protective devices (such as lightning arrestors, fuses, and others)
  • Instrument Transformer (such as Potential Transformer, Current Transformer)
  • Bus bar
  • Insulator

What are the types of Substation?

The electrical voltage is transmitted and distributed by using a power transformer, distribution transformer, and switchgear equipment. Basically, a 132KV substation is considered as the primary substation or high voltage substation or sometimes called a transmission substation. But 33KV substation is considered as the distribution substation or distribution voltage. Though there are various types of substations, we consider two main types of substation such as

  • Service requirement substation
  • Constructional feature substation

Service Requirement Substation

Those substations change voltage levels, improve power factors, and convert AC to DC electrical power such kinds of substations are called service requirement substations. There are various types of service requirement substations such as

Transformer Substation or transformer stations

Those substations change voltage levels by using power transformers such kinds of substations are called transformer substations or transformer stations. This substation is received power at the same voltage and transfers it to the other voltage. It is important to note that, most of the substations of the electrical power system is a transformer type substations.

Switching Substation 

Switching substations is one of the most important substations that operate by the switching system. The switching substation is used to stable the power in the incoming and outgoing lines it performs as a switching operation. It means that there is no change in voltage level in the switching substation.

Power Factor Correction Substation

The power factor correction substation is a very important station because sometimes the power factor becomes low but it is very important to improve the power factor due to reducing the power loss. The power factor improvement capacitor is an important component of this substation. Basically, a synchronous condenser or static capacitor is used in this substation.

Frequency Changer Substation   

The electrical supply frequency range is 50 Hz, or 60 Hz sometimes frequency becomes low or high. That substation is used to change the supply frequency such kind of substation is called a frequency changer substation. This type of substation basically used for industrial applications.

Converting Substation

Converting substation is a type of substation that is an essential substation where voltage conversion is required note that, our total power circuit carries Alternating Current (A.C.). Suppose somewhere needs D.C. then, you need to convert A.C. power into D.C. power, or sometimes D.C. power is converted to the A.C. power. This type of substation is called converting substation.   

Constructional Feature Substation

It is one of the important substation categories and also has several sub-categories. A constructional feature substation consists of a large number of electrical substation components and this substation provides reliable or continuous power supply. There are four types of constructional feature substations such as

Indoor Substation

The indoor substation is one of the ing substations in the power system. Indoor substation carries voltage up to 11KV these types of substations are installed indoors due to economic consideration. Sometimes indoor substations may be erected at voltage up to 66KV. The indoor substation is more reliable and takes small space to install and requires a lower operating cost.

Outdoor Substation

The outdoor substation is played an important role in the power system because the large voltage is delivered through this substation. Outdoor substations are used for all voltage levels of more than 60KV. It takes less time to build such substations but uses more space. Outdoor substations are mainly classified into two types, namely, pole-mounted substations and foundation-mounted substations. The outdoor substation consists of a very expensive component.

Underground Substation

The underground substation is made in a thickly populated area where underground components are available. The underground substations help bring high voltage electricity directly to the city center. The stations are environmentally friendly, almost indomitable, and have no planning problems faced by surface-built solutions.

Pole Mounted Substation

Pole mounted substation or distribution substation is an outdoor substation it is made of a four-pole or H pole structure. It is a distribution substation that establishes an overhead line. This is the cheapest form of the substation because it is not involved in any building work. The voltage range is not more than 11KV (sometimes uses 33K in special cases).

Types of Distribution Substation

An electrical substation is one of the major parts of the transmission and distribution of electricity to consumers. Basically, the AC distribution system consists of two parts, such as the primary distribution system and the secondary distribution system. Primary distribution system means that 11KV substation, if we explain then secondary transmission substation deliver 33KV, 66KV power to the primary distribution substation and voltage is step down to the 11KV, 6.6KV, 3.3KV by using step down transformer.


The standard voltage limit is 11KV. This 11KV three phase power line is supplied to the various distribution substations that is called secondary distribution substation. This 11KV voltage is stepped down to a known ratio of 11KV/400V by using step-down distribution transformer. The power line goes to the consumer locality by three phase four wire system. Those are three phase load (three-phase induction motor, or any three phase load) that takes three phase directly (400V). But residential load or single phase domestic load takes a power line and neutral those voltage limits of 230V.

What is an Electrical Power Grid Substation?

We know that power substation plays a crucial part to reach power near the consumer. An electrical power grid substation means that a very high voltage power line (230KV, 400KV) is connected there and multiple power lines can also be connected there. Basically, the power grid substation is located near the central point from where power can be transmitted to different locations. Basically, the purpose of the power grid substation is to step down the very high voltage level like 230KV/132KV, 230KV/33KV, or 400KV/132KV. This 132KV or 33KV high voltage transmission line runs to the different transmission substations to be sub-divided for the distribution.

What is 132KV Substation or 220KV Substation?

Electricity is generated at low voltage and transmits to the high voltage from one place to another place by the transmission conductor which is called an electrical transmission line. Basically, a 220KV substation or 132KV substation means that primary transmission substation. Basically, a 2220KV or 132KV transmission line runs from the generating station and meets at any substation to divide the voltage level for another electrical substation.

What is 33KV Substation?

Basically, 33KV Substation is an electrical substation and it is also called a secondary transmission substation. After ending 132KV line or 132KV receiving station power line is subdivided into some transmission lines which carry 33KV. This 33KV transmission line runs to another locality and meets any electrical substation to subdivide the voltage level which is called the 33KV substation. It is noted that after ending the secondary transmission line the primary distribution line (11KV) will start its journey.

What is Central Substation?

The central substation is an important part of the power plant. Whereas electrical power is divided (change voltage level). Basically, it is a high voltage electrical substation (132KV/33KV or 66KV/33KV). The central substation is a step down substation (voltage level is changed from high voltage to low voltage). High voltage switchgear equipment is also installed here. Such kind of substations is located at a far distance from the locality and enclosed brick walls to safe the adjacent people from unexpected electrical hazards.

What is Bus bar Arrangement in Substation?

The bus bar is an important component of the electrical substation. The electrical substations have three housing systems that can be used depending on the voltage and load. The choice of a particular system depends on various factors such as system voltage, substation location, degree of reliability, cost, etc. The substations have the following important bus-bar arrangements:

  • Single bus-bar arrangement substation
  • Single bus-bar with sectionalization substation
  • Duplicate bus-bar arrangement substation

Single Busbar Arrangement in Substation

As the name implies, it has a single bus bar and all incoming and outgoing lines are connected to it. The main advantages of this type of management are low initial cost, easy maintenance, and easy operation. However, the main problem with the single bus-bar system is that if the bus bar has to be repaired or there is a fault in the bus, the supply is completely disrupted.


This system is not used for voltages above 33KV. Indoor 11KV sub-stations often use single accommodation in substations. There are two 11KV incoming lines through circuit breakers and isolators connected to two 400V outgoing lines and transformers that step down the voltage level (11KV / 400V) and bus bars via circuit breakers.

Single bus bar with Sectionalization Substation?

In this system, the single bus is divided into twelve sections and the load is distributed evenly across all sections. Any two sections of the bus bar are connected by a circuit breaker and disconnectors. Two main advantages are claimed for this arrangement. First, if any defect occurs in any section of the bus, that part can be disconnected without affecting the supply from other sections.


Second, the repair and maintenance of any part of the bus bar can only be carried out by de-energizing that section, eliminating the possibility of closing the entire department. This system is used for voltages up to 33 kV. There are two 33 kV incoming lines and sections connected through the circuit breakers and disconnectors shown. Each 11 kV outgoing line is connected to a section via a transformer (33KV/11KV) and a circuit breaker. It is easy to see that each bus department behaves as a separate bus bar.

Duplicate bus-bar Arrangement Substation?

This system has two bus bars, an original bus bar, and an extra or spare bus bar. Each bus bar has the capacity to receive a full substation load. The incoming and outgoing lines can be connected to any bus breaker and disconnector bus bar with the help of a bus-bar coupler. Typically, inbound and outbound lines are connected to the main bus bar.


However, in case the main bus bar is repaired or there is a defect in it, it can be maintained by moving the supply continuity of the circuit to the additional bus bar. For voltages above 33kV, a duplicate bus-bar system is often used. Two 66KV incoming lines can be connected to the bus bar by a bus bar connector. Two 11KV outgoing lines are connected to the bus bars via transformers (66KV/11KV) and circuit breakers.

What is Instrument Transformer?

A modern power system consists of a bunch of valuable components. An electrical power line carries a large current in a thousand amperes and very high voltage. Basically, an Instrument transformer is used to measure the current and voltage of the electrical power lines. There are two types of instrument transformer

  • CT (Current Transformer)
  • PT (Potential Transformer) 

What is Current Transformer (CT)?

Basically, the Current transformer is considered a step-up transformer that steps down the current or decreases the line currently at a known ratio. The primary winding of the current transformer consists of one or more turns of thick wire these are connected in series with the power line. But the secondary winding of the current transformer consists of a large number of turns of fine wire with the line.

The current transformer (CT) is measured current and rated at 100/5 A. It means that, if the input current becomes high then the output current will be low. If the primary current becomes 50 A then the secondary current will be 2.5 A (50/2.5 A). It means that the current transformer will step down the line current by a factor of 20.  

What is Potential Transformer (PT)?

A potential transformer (PT) is a step own transformer that steps down the line voltage to a known ratio. The primary winding of the potential transformer consist of a large number of turns and the secondary winding of the Potential Transformer (PT) consist of a small number of turn by the thick conductor.

If the primary voltage or line voltage of the potential transformer (PT) becomes 66KV then the PT will give 110V as secondary voltage (66KV/110V). It means that if the line voltage becomes 66KV you will get 110 V in the secondary of the PT, for this reason, PT is a step-down transformer.

What is bus bar?

The bus bar is a very important substation component. The bus bar is a copper road or aluminum road or thin-walled tube where incoming and outgoing lines are connected. The bus bar cannot change the voltage level but it keeps stable the voltage level and the voltage level is changed by the transformer. Basically, three types of bus bar arrangements are used in the substation such as single-line bus bar, single-line bus bar with sectionalization, and duplicate bus bar.   

Electrical switchyard components

The switchyard components are an important part of the electrical power system. The switchyard components are used for switching and protection purposes. Basically, these are used for high voltage switching, protecting, and controlling purposes. There are different types of electrical switchyard components, such as

  • Conductors
  • Insulators
  • Lighting arresters (LA)
  • Instrument transformers (CT, PT)
  • High voltage power transformers
  • Relays
  • Bus bars
  • Circuit breakers

What is the difference between relay and fuse?

Relay and fuse both are crucial and more useable devices in the modern power system. We need to remember that relay is not an electrical fuse and the fuse is not a relay. It is true that the fuse is almost similar to the circuit breakers. Fuse and circuit breaker both are used for overcurrent and overvoltage protection purposes. Now we will compare between relay and fuse:

Relay is the electrically operated switchFuse is an electrical safety device that is used for the power system protection purposes
Relay is used to interrupt or connect the circuitFuse is the protective device that can interrupt the circuit.
Relay provides the signal to the circuit breakers to trip the circuitFuse limits the overcurrent and protects the circuit
Relay cannot work aloneFuse can work alone and protect the circuit from surge voltage

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