Substation: Duties;Service;Voltage;Importance;Design

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Classification Substation: Duties; Service Rendered; Operating Voltage; Importance; Design

Classification of Substation on the Basis of Nature of Duties


It could be classified into the following three categories:


  1. Step-Up or Primary Substations.

Such substations are usually associated with generating stations. The generated voltage, which is usually low ( 3.3, 6.6, 11 or 33 KV), is stepped up to primary transmission voltage so that huge blocks of power can be transmitted over long distance to the load centers economically.

2. Primary Grid Substations.

Such substations are located at suitable load centers along the primary transmission voltage is stepped down to different suitable secondary voltages. The secondary transmission lines are carried over to the secondary substations situated at the load centers where the voltage is further stepped down to sub-transmission or primary distribution voltages.

3. Step-Down or Distribution Substations

Such substations are located at the load centers, where the sub-transmission/primary distribution voltage is stepped down to secondary distribution voltage (415/240V). These are the substations which feed the consumers through distribution network and service lines.

Classification of Substations on the Basis of Service Rendered




On the basis of this, it can be classified as follows:

  1. Transformer Substations:

Transformers are installed on such substations to transform the power from one voltage level to another level as per needs.

2. Switching Substations:

Such substations are meant for switching operation of power lines without transforming the voltage. At such substations different connections are made between various transmission lines.

3. Converting Substations:


Such substations are meant for either converting ac to dc or vice versa or converting frequency from higher to lower or vice versa.

Classification of Substations on the Basis of Operating Voltage

It can be categorized as:


  1. High Voltage Substations ( HV Substations) involving voltage between 11 KV and 66 KV.
  2. Extra High Voltage Substations (EHV Substations) involving voltages between 132 KV and 400 KV.
  3. Ultra High Voltage Substations (USV Substations) operating on voltage above 400 KV.

Classification of Substations on the Basis of Importance

  1. Grid Substations.

These are the substations from where bulk power is transmitted from one pint to another point in the grid. These are important because any disturbance in these substations may cause the failure of the grid.

2. Town Substations:

These substations step-down the voltages at 33/11 KV for further distribution in the towns and any failure in such substations results in the failure of supply for whole of the town.

Classification of Substations on the Basis of Design

  1. Indoor Type Substation

In such substations the apparatus is installed within the substation building. Such substations are usually for a voltage up to 11 KV but can be erected for the 33 KV and 66 KV when the surrounding atmosphere is contaminated with impurities  such as metal corroding gases and fumes, conductive dust etc.

2. Outdoor Substation

(a) Pole Mounted Substations:

Such substations are erected for distribution of power in localities. Single stout pole or H-pole and 4-pole structures with suitable platforms are employed for transformers of capacity up to 25 KVA, 125 KVA and above 125 KVA (but up to 250 KVA) respectively.

(b) Foundation Mounted Substations:

For transformers of capacity above 250 KVA the transformers are too heavy for pole mounting. Such substations are usually for voltage of 33,000 volts and above.

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