hvdc transmission 2ppt

7/31/2019 Hvdc Transmission 2ppt

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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!

hvdc transmission 2ppt

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