hvdc transmission 2ppt
TRANSCRIPT
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HVDCTRANSMISSION
Under the
guidance of :Mrs. Shaija P J
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INTRODUCTIONA high- voltage direct current(HVDC)electric power transmission usesdirect current for the bulktransmission of electrical power, in
contrast with the more commonalternating current systems. For long-distance distribution, HVDC systemsare less expensive and suffer lower
electrical losses. For shorterdistances, the higher cost of DCconversion equipment compared to anAC system may be warranted whereother benefits of direct current links
are useful.
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The first dc link was set up in 1954in between Swedish main land andthe island of Gotland.The use of an HVDC link in an acsystem requires converter stationsat each end of the line.
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ADVANTAGES
Advantages of
dctransmission
TechnicalAdvantag
es
EconomicAdvantag
es
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TechnicalAdvantagesReactive power requirement
System stabilityShort Circuit CurrentIndependent Control of ac systemFast change of energy flowLesser Corona Loss and Radio interference
Greater Reliability.
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No limits in transmitteddistance
Direction of power flow can be
changed very quickly
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Economic advantages
DC lines and cables are cheaper thanac lines or cables.
The towers of the dc lines arenarrower, simpler and cheapercompared to the towers of the ac
lines.Line losses in a dc line are lower thanthe losses in an ac lines.
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Comparison between the pricesof AC & DC
Transmission
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Types of DC links
Monopolar
Bipolar
Homopolar
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Monopolar
link
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Bipolar Link
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Two terminal DC link point to pointtransmission.
Back to Back DC linkDC line in Parallel with AC link.Multi-Terminal DC link.
Incorporating HVDC into ACsystems
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Thyristor valvesConverter TransformerDC ReactorHarmonics Filtering EquipmentControl Equipment
Reactive power compensation
CONVERTER STATION
EQUIPMENT
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Most dc transmission lines use ground returnfor reasons of economy and reliability
Ground return are used by the monopolarand the bipolar link for carrying the return
current.The ground path has a low resistance and,
therefore low power loss as compared to ametallic conductor path provided the ground
electrodes are properly designed.The resistance of the ground path is
independent of the depth of the line.
GROUND RETURN
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The Design of grounding electrodes for lowcost of installation and maintenance
Location and screening of electrodes so that
ground currents cause negligible electrolyticcorrosion of buried and immersed metallicstructures.
PROBLEMS
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HVDC system requires a properly designedearth electrode at each station.
The electrode is situated at a safe distance (5
to 30 km) from the station.The earth electrode at one of the station acts
as a anode and at the other end acts as acathode.
EARTH ELECTRODE
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GTOs have come into use.Use of active ac and dc filters.
Advanced fully digital control systems usingoptical fibers.
RECENT ADVANCES
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Recent studies indicate that HVDC systems arevery reliable.
The data collected from 31 utilities says thatforced unavailability of energy due to theconverter station is 1.62%
The scheduled unavailability of energy is about
5.39%.
CONCLUSION
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Thank you!