SUB
The assembly of apparatus used to
The assembly of apparatus used to
change
change
some characteristic(e.g. Voltage, a.c to
some characteristic(e.g. Voltage, a.c to
d.c,
d.c,
frequency, power factor etc) of electric supply is
frequency, power factor etc) of electric supply is
called a sub-station
The assembly of apparatus used to
The assembly of apparatus used to
change
change
some characteristic(e.g. Voltage, a.c to
some characteristic(e.g. Voltage, a.c to
d.c,
d.c,
frequency, power factor etc) of electric supply is
frequency, power factor etc) of electric supply is
called a sub-station
•
•
It should be located at the
It should be located at the
centre of gravity
centre of gravity
of load
of load
•
•
It should be easily operated and maintained
It should be easily operated and maintained
•
•
It should provide
It should provide
safe and reliable
safe and reliable
arrangement
arrangement
•
Sub-stations
Sub-stations
Service Service requirement requirement Constructional Constructional features features
Transformer sub stationsTransformer sub stations : these are used to change : these are used to change the voltagethe voltage
levels of supply
levels of supply
switching sub stationsswitching sub stations: they : they simply perfome switching operationssimply perfome switching operations
of power lines
of power lines
Power factor sub stations Power factor sub stations: they improve the power factor of : they improve the power factor of thethe
system by using
system by using synchronous condenserssynchronous condensers
Frequency sub stations Frequency sub stations: those sub stations which change supply: those sub stations which change supply
frequency
frequency
Converting sub stationsConverting sub stations: those sub stations which change a.c.: those sub stations which change a.c.
power to d.c. power
power to d.c. power
Industrial sub stationsIndustrial sub stations: those sub stations which supply power to: those sub stations which supply power to
industries
industries
Substations are classified as……..
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…
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
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
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…
INSULATORS
: insulators serve two purposes1) they support conductors(busbars)
2) confine the current to the conductors
most commonly used material for manufacture of insulators is porcelain.
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.
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
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.
Current transformers: current transformer in
essentially a step up transformer which steps down the current to a known ratio.
voltage transformer: it is essentially a step down transformer and steps down the voltage to a known ratio.
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
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
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
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
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
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
Compact GIS systems are essentially three phase common systems in which the elements such as three phase circuit breaker, current transformer etc…. Are placed
These are used in outdoor substations .highly integrated substations are ready to install substations.
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
The main parts of GIS are…….
gas circuit
seals and gaskets
disconnectors
earth switch
Circuit breaker
Current transformer
Plug in joints
Enclosure
Expansion joints
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
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.
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
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
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
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 S NO 145KV 170KV 245KV
