1. SUB-STATIONS

2. INTRODUCTION
The assembly of apparatus used to change some characteristic(e.g. Voltage, a.c to d.c, frequency, power factor etc) of electric supply is called a sub-station

3. SITE SELECTION …..
It should be located at the centre of gravity of load
It should be easily operated and maintained
It should provide safe and reliable arrangement
It should involve minimum capital cost

4. CLASSIFICATION OF SUB-STATIONS
Service requirement
Constructional
features

5. ACCORDING TO SERVICE REQUIREMENT
Substations are classified as……..
Transformer sub stations : these are used to change the voltage levels of supply
switching sub stations: they simply perfome switching operations of power lines
Power factor sub stations: they improve the power factor of the system by using synchronous condensers
Frequency sub stations: those sub stations which change supply frequency
Converting sub stations: those sub stations which change a.c. power to d.c. power
Industrial sub stations: those sub stations which supply power to industries

6. TRANSFORMER SUB-STATIONS
Transformer substations are classified into 4 types these are……..
step up substation: the generation voltage is stepped up to high voltage
Primary grid substation: here the voltage level is step down to 66kv from 220kv for secondary transmission
Secondary substation: the voltage level is further step down to 11kv and these substations are generally outdoor type
Distribution substation: the electric power from 11kv lines is delivered to distribution substation. These are generally located near consumer localities…

7. ACCORDING TO CONSTRUCTIONAL FEATURES
According to constructional features, the sub stations are classified as:
Indoor sub station: these substations can be installed for voltages up to 11kv
Outdoor sub station: for voltages beyond 66kv these type of sub stations can be installed
Underground sub stations: in thickly populated areas, the space available is less so we install these type of substations
Pole mounted substations: this is an outdoor substation with equipment installed overhead on h-pole or 4 pole structure

8. INDOOR SUBSTATION…..

9. BLOCK DIAGRAM>>>>>>

10. pole mounted substation
It is a schematic view of pole mounted substation……

11. POLE MOUNTED SUBSTATION……

12. UNDERGROUND SUBSTATION……
While designing a underground sub station the following points are to be followed:
the size of substation should be minimum
There should be reasonable access for both equipment
There should be provision for emergency lights and protection against fire
There should be good ventilation
the transformers,switches,fuses should be air cooled to avoid bringing oil into premises

14. Schematic view………

15. SYMBOLS FOR EQUIPMENT IN SUB STATIONS

17. EQUIPMENT IN A TRANSFORMER SUB STATION.
EQUIPMENT IN A TRANSFORMER SUB STATION
Electric substations are the part of power systems and used for transferring power from generating points to load centres.some of important components are…
BUS BARS: various incoming and out going circuits are connected to bus bars.busbars receive power from incoming circuits and deliver power to out going circuits.

18. INSULATORS: insulators serve two purposes
1) they support conductors(busbars)
2) confine the current to the conductors
most commonly used material for manufacture of insulators is porcelain.

19. ISOLATING SWITCHES: in sub stations it is often desired to disconnect a part of system for general maintenance and repairs. this is accomplished by an isolating switch or isolators.

20. Circuit breaker: circuit breaker is used for switching during normal and abnormal conditions. it is used to interrupt short circuit currents .there are many types of circuit breakers..
1) air blast circuit breaker.
2) oil circuit breaker
3) sf6 circuit breaker

21. power transformers: these are used to step down or step up a. c
power transformers: these are used to step down or step up a.c. voltages and to transfer electrical power from one voltage level to another.

22. Current transformers: current transformer in essentially a step up transformer which steps down the current to a known ratio.

23. voltage transformer: it is essentially a step down transformer and steps down the voltage to a known ratio.

24. metering and indicating instruments: there are several metering and indicating instruments installed in a sub station to maintain watch over the circuit quantities.
in addition to these there may be following equipment in a substation.
1) fuses
2) carrier current equipment
3) sub station auxiliary supplies

25. BUS BAR ARRANGEMENTS IN A SUBSTATION
Single bus bar system…

26. Duplicate bus bar system…..

27. Key diagram of 66/11kv substation

28. Key diagram of 11/440v indoor substation

29. Thank you..