1. SUB-STATIONS

2.  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. • 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. Sub-stations
Service
requirement
Constructional
features

5.  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
Substations are classified as……..

6. 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, 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

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

12. 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

17.  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.
.
Electric substations are the part of power systems and used for
transferring power from generating points to load centres.some of
important components are…

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.
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. Single bus bar system…

29. GAS INSULATED SUBSTATION

30. Gas Insulated substations use
sulphur hexa fluoride(SF6) gas which
has superior dielectric properties.
Gas insulated substations are used
where there is space for providing
the substation is expensive in large
cities and towns

31. TYPES OF GAS INSULATED SUBSTATIONS
Gas insulated substations are classified according to
the type of configurations as………..
 isolated phase module
 3-phase common modules
 hybrid modules
Compact modules
Highly integrated systems

32. The individual circuit elements such as a pole of a circuit breaker, a single
pole isolator, one phase assembly of a current transformer etc..are
connected together forms an isolated phase GIS module.

33. In this type of module a three phase bay is assembled using the desired
number of three phase elements. This reduces the total number of
enclosures to one third.

34. It is the combination of isolated phase and three phase common
elements is used to achieve an optimal solution. Hybrid GIS technology
has gained popularity, specially in the medium and low voltage range

35. Compact GIS systems are essentially three phase common systems
in which the elements such as three phase circuit breaker, current
transformer etc…. Are placed

36. These are used in outdoor substations .highly integrated substations
are ready to install substations.

38. The high voltage conductor made up of
copper or aluminum is centrally placed in a
tabular metal enclosure. In isolated phase
GIS ,coaxial bus bar are common

39. The main parts of GIS are…….
 gas circuit
 seals and gaskets
 disconnectors
 earth switch
Circuit breaker
Current transformer
Plug in joints
Enclosure
Expansion joints

41. Gas circuit : gas circuit has to maintain the dual
purpose (i.e. arc interruption and insulation). Gas
circuit should maintain the pressure throughout its
life period so there should be no leakages
SEALS AND GASKETS : seals and gaskets are used to
capture the SF6 gas lekages.these are manufactured
with nitrile rubber and viton. These serves sealing
purpose

42. Disconnectors or isolators are used for electrical
isolation of circuit parts.
They are slow acting and operating at off load.
Disconnectors must be carefully designed and
tested to be able to break small charging current
without generating too higher over voltage.

43. Circuit breaker is a metal clad and uses SF6 gas for the
purpose of insulation and fault interruption. The circuit
breaker is directly connected to either current transformers or
isolators

45. fast earth switch: these are used to
protect the circuit connected current
transformer, voltage transformer
Maintenance earth switch: these are used
for grounding the high voltage conductors
during maintenance

46. PLUG IN JOINTS: these are designed in such a way that
they can carry rated full load current uninterruptedly
and can carry heavy transient currents types of plug in
joints are
Static joints
Quasi static joints

47. S.NO 145KV 170KV 245KV
1 Bay width
(m)
1.5 2.0 2.0
2 Bay depth 3.3 3.35 3.4
3 Bay height 3.2 3.4 3.4
4 Floor area
(sq.m)
4.95 6.7 6.8
5 Volume 15.84 22.78 23.12
6 Weight 3800 5000 5700

48. GIS have no risk for fire and explosion due
to leakage of oil.
They generate no noise and have no radio
interference.
The maintainence of GIS is free.
It offers solutions,
-Industrial areas where space and
pollution problems .
-Mountain areas where ice and snow
are major problems.

49. Gas insulations tend to be much more
expensive than air insulated installations
with the same ratings.
Care should be taken that no dust
particles enter into the live compartments
which results in flash over.
When fault occurs internally the
diagnosis of the fault and rectifying takes
very long time.