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“HVDC TRANSMISSION”

UCE BURLA

HEMANT KUMAR NAYAK ELECTRICAL ENGGINERING REG. NO.-0401101184

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INTRODUCTION

•Now a days large blocks of power are needed to be transmitted.

•There arises some technical problems of transmitting power to such a long distance using ac.

•In the view of the draw backs of ac the HVDC transmission has come into picture.

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•The first dc link was set up in 1954 in between Swedish main land and the island of Gotland.

•The use of an HVDC link in an ac system requires converter stations at each end of the line.

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HISTORYHISTORY IN the initial stages dc used to be IN the initial stages dc used to be

employed for generation ,transmission employed for generation ,transmission and distribution of electric power. The and distribution of electric power. The first 110V D C central electric station was first 110V D C central electric station was installed by Edison in New York installed by Edison in New York in1882.with the introduction of in1882.with the introduction of transformer and 3-phase ac system the transformer and 3-phase ac system the situation changed in favors of ac .for situation changed in favors of ac .for many reasons ,such as facility of many reasons ,such as facility of transformations of voltages from one level transformations of voltages from one level to another ,better performance of ac to another ,better performance of ac motors and superiority of ac generators in motors and superiority of ac generators in comparison to dc generator ,the power comparison to dc generator ,the power was generated ,transmitted, distributed was generated ,transmitted, distributed and utilized in the form of ac. But the and utilized in the form of ac. But the supporters of DC carried out extensive supporters of DC carried out extensive research on dc field And found the research on dc field And found the advantages of dc in high and extra high advantages of dc in high and extra high voltage of transmission for long distance .voltage of transmission for long distance .

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with the successful development of high power with the successful development of high power thyristers the HVDC transmission become thyristers the HVDC transmission become technically and commercially viable alternative to technically and commercially viable alternative to EHV/UHV-AC transmission.EHV/UHV-AC transmission.

The first dc link was setup in 1954 between The first dc link was setup in 1954 between Swedish mainland and island of got land .This was Swedish mainland and island of got land .This was a Monopolar ,100KV,20MW,cable system making a Monopolar ,100KV,20MW,cable system making use of sea return .the England –France cross use of sea return .the England –France cross Channel dc link was commissions in1961.this was Channel dc link was commissions in1961.this was bipolar +-100KV,160MW,Cable system over a bipolar +-100KV,160MW,Cable system over a distance of 65 KM .since then more and more distance of 65 KM .since then more and more HVDC system have been set up in the world.HVDC system have been set up in the world.

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HVDC Transmission has also been HVDC Transmission has also been introduced in India .A +-introduced in India .A +-500kv ,1500mw,810km bipolar HVDC line 500kv ,1500mw,810km bipolar HVDC line has already been set up between Rihand has already been set up between Rihand and Delhi. it is designed to operate in and Delhi. it is designed to operate in bipolar ,monopolar ground return ,and bipolar ,monopolar ground return ,and Monopolar metallic return mode. Monopolar metallic return mode.

Vindhyachal HVDC back to back system Vindhyachal HVDC back to back system for exchanging power between northern for exchanging power between northern and western region in either direction .and western region in either direction .

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Chandarpur-padghe bipolar system (-Chandarpur-padghe bipolar system (-+500kv,1500mw,736km),Jeypore +500kv,1500mw,736km),Jeypore back to back project(2*250mw),ana back to back project(2*250mw),ana Mau back to back project Mau back to back project (2*250mw)are also proposed .(2*250mw)are also proposed .

At present the world has over 50 At present the world has over 50 HVDC schemes in operation for a total HVDC schemes in operation for a total capacity of more than 50,000mw and capacity of more than 50,000mw and the capacity is increasing by about the capacity is increasing by about 2000mw every year.2000mw every year.

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why high voltage for why high voltage for transmission?transmission?

Because with increase in transmission voltage Because with increase in transmission voltage with same power supply the current in the with same power supply the current in the conductor decreases. so size of the conductor conductor decreases. so size of the conductor decreases and since current in the conductor decreases and since current in the conductor decrease so losses are decreases and hence decrease so losses are decreases and hence efficiency of the line increases. so high voltage is efficiency of the line increases. so high voltage is used in transmitting the power .also the voltage used in transmitting the power .also the voltage regulation will improve.regulation will improve. Reduction of electrical losses, increase in Reduction of electrical losses, increase in

transmission efficiency ,improvement of transmission efficiency ,improvement of voltage regulation and reduction in conductor voltage regulation and reduction in conductor material requirement.material requirement.

Line losses are reduced since line losses are Line losses are reduced since line losses are inversely proportional to transmission voltage .inversely proportional to transmission voltage .

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Transmission efficiency increases because of Transmission efficiency increases because of reduction in line losses .reduction in line losses .

Voltage regulation will improve because of Voltage regulation will improve because of reduction of percentage of line drop .reduction of percentage of line drop .

Size of the conductor material required is Size of the conductor material required is inversely proportional to the square of inversely proportional to the square of supply voltage .supply voltage .

Flexibility for future system growth.Flexibility for future system growth. Increase in transmission capacity of the line .Increase in transmission capacity of the line . Increase of surge impedance loading(load Increase of surge impedance loading(load

carrying capability of it’s supply line ).carrying capability of it’s supply line ).

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Disadvantage of HVAC?Disadvantage of HVAC? with increase in distance and voltage the with increase in distance and voltage the

problems associated with ac systems increase. these problems associated with ac systems increase. these problems are of problems are of

Corona loss and radio interference.Corona loss and radio interference. Heavy supporting structure and erection difficulties .Heavy supporting structure and erection difficulties . Insulating problem .Insulating problem . Stability problem.Stability problem. Current carrying capacity.Current carrying capacity. Ferranti effect.Ferranti effect. Surge impedance loading.Surge impedance loading. Mechanical vibrations and oscillations.Mechanical vibrations and oscillations. Radio interference.Radio interference.

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PRINCIPLE OF OPERATION OF PRINCIPLE OF OPERATION OF HVDC LINEHVDC LINE

It required two ac system which are to be It required two ac system which are to be connected by dc link.connected by dc link.

Step-up transformer at sending end and step-down Step-up transformer at sending end and step-down transformer at receiving end.transformer at receiving end.

Two Converter station one at sending end for Two Converter station one at sending end for converting ac to dc and other at receiving end for converting ac to dc and other at receiving end for converting dc to ac.converting dc to ac.

By changing the firing angle it act as rectifier(0 to By changing the firing angle it act as rectifier(0 to 90) deg. And inverter (90 to 180)deg. .so it can 90) deg. And inverter (90 to 180)deg. .so it can operate in bidirectional flow of power.operate in bidirectional flow of power.

The dc out-put voltage magnitude can be controlled The dc out-put voltage magnitude can be controlled by changing the firing angle of the converter.by changing the firing angle of the converter.

In practical HVDC converter station three-phase In practical HVDC converter station three-phase bridge converter are employed at both end .bridge converter are employed at both end .

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PRINCIPLE OF OPERATION OF HVDC LINEPRINCIPLE OF OPERATION OF HVDC LINE

It required two ac system which are to be It required two ac system which are to be connected by dc link.connected by dc link.

Step-up transformer at sending end and step-down Step-up transformer at sending end and step-down transformer at receiving end.transformer at receiving end.

Two Converter station one at sending end for Two Converter station one at sending end for converting ac to dc and other at receiving end for converting ac to dc and other at receiving end for converting dc to ac.converting dc to ac.

By changing the firing angle it act as rectifier(0 to By changing the firing angle it act as rectifier(0 to 90) deg. And inverter (90 to 180)deg. .so it can 90) deg. And inverter (90 to 180)deg. .so it can operate in bidirectional flow of power.operate in bidirectional flow of power.

The dc out-put voltage magnitude can be controlled The dc out-put voltage magnitude can be controlled by changing the firing angle of the converter.by changing the firing angle of the converter.

In practical HVDC converter station three-phase In practical HVDC converter station three-phase bridge converter are employed at both end .bridge converter are employed at both end .

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ADVANTAGES ADVANTAGES

Advantages of dc transmission

Technical Advantages

EconomicAdvantages

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Technical AdvantagesTechnical Advantages Reactive power requirementReactive power requirement System stabilitySystem stability Short Circuit CurrentShort Circuit Current Independent Control of ac systemIndependent Control of ac system Fast change of energy flowFast change of energy flow Lesser Corona Loss and Radio interferenceLesser Corona Loss and Radio interference Greater Reliability.Greater Reliability.

o No limits in transmitted distance

o Direction of power flow can be changed very quickly

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Economic advantagesEconomic advantages

•DC lines and cables are cheaper than ac lines or cables.

•The towers of the dc lines are narrower, simpler and cheaper compared to the towers of the ac lines.

•Line losses in a dc line are lower than the losses in an ac lines.

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Comparison between the prices of AC & Comparison between the prices of AC & DCDC

TransmissionTransmission

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Types of DC links

Monopolar

Bipolar

Homopolar

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Monopolar linkMonopolar link

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Bipolar LinkBipolar Link

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Incorporating HVDC into AC systemsIncorporating HVDC into AC systemsTwo terminal DC link point to point Two terminal DC link point to point

transmission.transmission.Back to Back DC linkBack to Back DC linkDC line in Parallel with AC link.DC line in Parallel with AC link.Multi-Terminal DC link.Multi-Terminal DC link.

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ESSENTIAL PARTS OF HVDC ESSENTIAL PARTS OF HVDC SYSTEMSYSTEM

AC sub station and HVDC sub AC sub station and HVDC sub station at each terminal.station at each terminal.

Interconnecting HVDC lines.Interconnecting HVDC lines.Electrode lines and earth Electrode lines and earth

electrodes.electrodes.

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MAIN PARTS OF HVDC MAIN PARTS OF HVDC TERMINAL SUBSTATIONTERMINAL SUBSTATION

AC switchyard.AC switchyard. Thyristor valves.Thyristor valves.o Converter Transformer.Converter Transformer. DC Reactor.DC Reactor. Harmonics Filtering Equipment.Harmonics Filtering Equipment. Control Equipment.Control Equipment. Reactive power compensation.Reactive power compensation. HVDC yard.HVDC yard. Electrical and mechanical auxiliaries.Electrical and mechanical auxiliaries.

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GROUND RETURNGROUND RETURN

Most dc transmission lines use ground return Most dc transmission lines use ground return for reasons of economy and reliabilityfor reasons of economy and reliability

Ground return are used by the monopolar and Ground return are used by the monopolar and the bipolar link for carrying the return current. the bipolar link for carrying the return current.

The ground path has a low resistance and, The ground path has a low resistance and, therefore low power loss as compared to a therefore low power loss as compared to a metallic conductor path provided the ground metallic conductor path provided the ground electrodes are properly designed.electrodes are properly designed.

The resistance of the ground path is The resistance of the ground path is independent of the depth of the line.independent of the depth of the line.

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PROBLEMSPROBLEMS

The Design of grounding electrodes for The Design of grounding electrodes for low cost of installation and low cost of installation and maintenancemaintenance

Location and screening of electrodes Location and screening of electrodes so that ground currents cause so that ground currents cause negligible electrolytic corrosion of negligible electrolytic corrosion of buried and immersed metallic buried and immersed metallic structures.structures.

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EARTHEARTH ELECTRODEELECTRODE

HVDC system requires a properly HVDC system requires a properly designed earth electrode at each designed earth electrode at each station.station.

The electrode is situated at a safe The electrode is situated at a safe distance (5 to 30 km) from the station.distance (5 to 30 km) from the station.

The earth electrode at one of the The earth electrode at one of the station acts as a anode and at the station acts as a anode and at the other end acts as a cathode.other end acts as a cathode.

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RECENT ADVANCESRECENT ADVANCES

GTO’s have come into use.GTO’s have come into use.Use of active ac and dc filters.Use of active ac and dc filters.Advanced fully digital control Advanced fully digital control

systems using optical fibers.systems using optical fibers.

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CONCLUSIONCONCLUSION

Recent studies indicate that HVDC Recent studies indicate that HVDC systems are very reliable.systems are very reliable.

The data collected from 31 utilities The data collected from 31 utilities says that forced unavailability of says that forced unavailability of energy due to the converter station is energy due to the converter station is 1.62%1.62%

The scheduled unavailability of energy The scheduled unavailability of energy is about 5.39%.is about 5.39%.

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Thank you!Thank you!