Features and Classification of Substations

A substation can be defined as an assembly of apparatus used to change some characteristics like voltage, AC, DC, frequency, power factor, etc., of electric supply.

Substations play a key role in power systems. The continuity of supply depends largely upon the successful operation of substations. Thus, it is imperative to exercise utmost care while designing and building a substation.

Some of the key factors to consider when planning and layout a substation include:

• It should be located at a proper site i.e. it should be located at the centre of gravity of load.
• It should provide safe and reliable arrangement. Safety consideration must be given to the maintenance of regulation clearances, facilities for carrying out repairs and maintenance, abnormal occurrences such as possibility of explosion or fire etc.
• It should be easily operated and maintained.
• It should involve minimum capital cost.

The Classifications of Substations

Substations can be broadly classified according to:

• Service requirement
• Construction features

Classification of Substations according to Service Requirement

A substation may be required to change the voltage level or improve power factor or convert AC power to DC power etc. As per the service requirement, substations may further be classified into:

Transformer Substations

These are substations that change the voltage level of electric supply. These substations receive power at some voltage and deliver it at some other voltage. Clearly, the transformer is the main component in such substations. Most of the substations in the power systems are of this type.

Converting Substations

These are substations that change AC power into DC power. They receive AC power and convert it into DC power with the help of appropriate equipment such as ignitron to supply for given purposes such as traction, electroplating, electric welding, etc.

Switching Substations

These substations do not change the voltage level, that is, the incoming and outgoing lines have the same voltage. But, they simply perform the switching operations of power lines.

Power factor correction Substations

These are substations that improve the power factor of the system. They are generally located at the receiving end of the transmission lines. These substations use synchronous condensers as the power factor improvement equipment.

Industrial Substations

These are substations which supply power to individual industrial needs.

Frequency changer Substations

These are substations that change the supply of frequency. Frequency change many needed for industrial utilization.

Related: Types of Busbar Arrangements in Grid Stations and Substations

Classification of Substations as Per Constructional Features

A substation typically consists of many components like circuit breakers, fuses, switches, instruments, etc. that must be housed properly to ensure the continuous and reliable service. As per constructional features, the substations are classified as:

Indoor Substations

For voltages up to 11 kV, the apparatus of the substation is installed indoor due to economic considerations. However, when the atmosphere is contaminated with impurities, these substations can be erected for voltages up to 66 kV.

Outdoor Substations

For voltages beyond 66 kV, equipment is often installed outdoor. This is due to the fact that, for such voltages, the clearances between conductors and the space needed for switches, circuit breakers and other apparatus becomes so great that it is not economical to install the equipment indoor.

Underground Substations

In highly populated areas, the space available for equipment and building may be limited and the cost of land may also be high. Under such circumstances, the substations are created underground.

Pole-mounted Substations

This is an outdoor substation with equipment that is installed overhead on H-pole or 4-pole structure. It is the most economical form of substation for voltages not exceeding 11 kV (or 33 kV in some cases). Electric power is often distributed in localities through such substations.

Also Read: Key Factors to Consider In Substation Design