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HVDC IN
FUTURE
TRANSMISSION
SYSTEM
By:
IYAPPAN.M
B.E., EEE.,
ARUNAI ENGINEERING
COLLEGE
[email protected]
SANTHOSH.S
B.E., EEE.,
ARUNAI ENGINEERING
COLLEGE
[email protected]
REASONS FOR AC
GENERATION AND
TRANSMISSIONS
Due to ease oftransformation ofvoltage levels (simple
transformer action)
and rugged squirrel
cage motors,
Alternating Current is
universally utilized.
Both for Generationand Loads and hence
for Transmission.
Generators are atremote places, away
from the populated
areas i.e. the loadcenters
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]
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They are either PitHead Thermal or
Hydel
Voltage is boosted upto 220 or 400 KV by
step-up transformers
for transmission to
Loads.
COMPARISON OF
HVAC & HVDC
SYSTEMS
Conventionally powertransmission is effected
through HVAC systems
all over the world.
HVAC transmission ishaving sever limitations
like line length,
uncontrolled power
flow, over/low voltages
during lightly/over
loaded conditions,stability problems, fault
isolation etc.
Considering thedisadvantages of HVAC
system and the
advantages of HVDCtransmission, power grid
has chosen HVDC
transmission for
transferring 2000 mw
from ER to SR.
HVDC: Uses Less
Current
oDirect current: Rollalong the line;
opposing force
friction (electrical
resistance).
oAC current willstruggle against
inertia in the line
(100times/sec)-
current inertia
inductance-reactive
power.
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DC HAS GREATER
REACH:
Distance as well asamount of Power
determine the choice of
DC over AC.
DIRECT CURRENT
CONSERVES
FOREST
AND SAVES LAND
Fewer support TOWER,less LOSSES.
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ADVANTAGES OF
HVDC OVER HVAC
TRANSMISSION
Controlled power flowis possible very
precisely
Asynchronous operationpossible between
regions having differentelectrical parameters
No restriction on linelength as no reactance in
DC lines
Stabilizing HVACsystems -dampening of
power swings and subsynchronous frequencies
of generator.
Cheaper than HVACsystem due to less
transmission lines & less
right of way for the
same amount of power
transmission
Important Milestones
in the Development of
HVDC technology
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Hewitts mercury-vapour rectifier, which
appeared in 1901.
Experiments withthyristors in Americaand mercury arc valves
in Europe before 1940.
First commercial HVDCtransmission, Gotland 1
in Sweden in 1954.
First solid statesemiconductor valves in
1970.
First microcomputerbased control equipment
for HVDC in 1979.
Highest DCtransmission voltage
(+/- 600 kV) in Itaip,Brazil, 1984.
First active DC filtersfor outstanding filtering
performance in 1994.
First CapacitorCommutated Converter
(CCC) in Argentina-Brazil interconnection,
1998
First Voltage SourceConverter for
transmission in Gotland,
Sweden ,1999
PURPOSE &FUNCTION OF
THYRISTOR VALVE
Connects AC phases toDC system
Conduct High Current currents upto 3000A
without the requirement
of paralleling of
thyristors
Block High Voltage Blocks high voltage in
forward and reversedirection up to 8KV
Controllable thyristortriggering /conduction
possible with the gate
firing circuits
Fault tolerant and robust1122--PPuullssee CCoonnvveerrttoorr
BBrriiddggee
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HHIIGGHHLLIIGGHHTTSS Commonly adopted in
all HVDC applications
Two 6 pulse bridgesconnected in series
30 phase shift betweenStar and Delta windings
of the converter
transformer
Due to this phase shift,5th and 7th harmonics are
reduced and filtering
higher order harmonics
is easier
