Substations serve as sources of energy supply for local areas. Main functions are to receive electrical energy transmitted at high voltage from power generating station, reduce voltage for local distribution and provides switching facilities.


Substations are classified in many ways such as on the basis of-

  • Nature of Duties

  • Service rendered

  • Operating Voltage

  • Importance

  • Design

Substation on The Basis of Nature of Duties:

In this basis Substations may classified into Three Categories as follows:

Step-Up or Primary Substation:  These are usually associated with generating stations. The generated voltage are usually low such as 3.3KV, 6.6KV, 11KV or 33KV is stepped up to primary transmission voltage so that huge power can be transmitted over long distance to the load center.

Primary Grid Substation: These are located at load center along the primary transmission line. In this substations primary transmission voltage is stepped down to different secondary voltages.

Step-Down or Distribution Substation: Such Substation are located at the load center. Where primary voltage is stepped down to secondary distribution voltage to 440 V or 230 V .

Substation on The Basis of Service Rendered: 

In this basis Substations may also classified into Three Categories as follows:

Transformer Substation: Transformer are installed on such substation to transform power from one voltage level to another.

Switching Substation: such substation are for switching operation of power lines without transforming the voltage level.

Converting Substation: Such substation are for converting Ac to DC or DC to AC or converting frequency higher to lower or lower to heigher.

Substation on The Basis of Operating Voltage:

according to operating voltages these substation also classified into three categories as follows:

High voltage (HV) Substation:- voltages between 11KV and 66KV

Extra High Voltage ( EHV) substation:- voltage between 132KV and 400KV

Ultra High Voltage (UHV):- voltage above 400KV.

Substation on The Basis of Importance:

In this basis Substations may classified into Two Categories as follows:

Grid Substation: These are the substation from where bulk power is transmitted from one point to another point in the grid.

Town Substation: These substation step-down the voltage at 33KV or 11KV for further distribution in towns.

Substation on The Basis of Design:

there are in two type as follows:

Indoor Substation: In these  type substation equipment are installed within the substation building . such are usually 11KV , 33KV and 66KV.

Outdoor Substation: These substation are further subdivided into two parts. as follows:

Pole Mounted: Such substation are created for distribution of power in localities.

Foundation Mounted: For transformer capacity above 250KVA the transformer are too heavy for pole mounting for that foundation mounted substation. operating voltage above 33KV.


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