Sub Station
The assembly of apparatus used to change some characteristics of electrical supply called the sub station
· It should be located at proper site
· It should provide safe and reliable arrangements
· It should be easily maintained and operated
· It should involve minimum capital cost
Classification of Substation
According to Service Requirements
· Transformer Substation
· Rectifier Substation
· Switching substation
· Power factor correction substation
· Converter substation
· Frequency changer substation
· Industrial substation
According to Constructional Features
· Indoor substation
· Outdoor substation
· Pole mounted substation
· Underground substation
Merits and Demerits
Merits of Indoor Substation
- Less space requirement and running cost
- Low voltage values
- More weather protection and life of equipments
Demerits of Indoor substation
- Erection time is more
- Future expansion and operation is complex
- Fault location identification and correction is difficult
- Dead investment is more
Merits of Outdoor substation
- Erection time is less
- Any values of voltage is used
- Fault location and correction is easy
- Capital investment is low
- Maintenance and operation is very easy
Demerits of Outdoor substation
- High running cost
- More requirements of space
- Life of equipments is less compare to indoor substations
Merits of Pole mounted substation
- Less space requirement
- Future expansion and fault location and correction is easy
- Easy operation and maintenance
Demerits of Pole mounted substation
- Erection is complex
- Voltage rating is low
- Running cost is higher
- Life of equipments is less
Merits of Underground substation
- Rating of substation is higher
- Running cost is less
- Operation is easy with neat arrangements
Demerits of Underground substation
- Space requirement and erection time is more
- Capital cost and Dead investment is more
- Fault correction and location is complex
- Future expansion is complex
Equipments in substation
- Insulators
- Conductors
- Relay and Circuit Breakers
- Transformers
- Current carrier equipments
- Fuses and switchyard
- Control cable
- Conduit system
- Disconnector switches and Isolators
- Control room
- Lightning arrestors
Layout of Substation
Bus bar Arrangements
- Single bus bar arrangement
- Main and auxiliary bas bar arrangement
- Double bus double breaker arrangement
- Sectionalized double bus arrangement
- Ring main bus bar arrangement
Isolators and Circuit Breakers
- Operation (Isolator) Manual
- Condition (Isolator) Off Load
- Excitation (Isolator) Mechanical
- Operation (C.B.) Automatic
- Condition (C.B.) On Load
- Excitation (C.B.) Relay Trip Coil
Current Transformer (C.T.)
- Thick wire
- Less winding
- Series connected
