RECENT TRENDS IN HVDC RECENT TRENDS IN HVDC TRANSMISSIONTRANSMISSION

PREPARED BY PREPARED BY PIYUSH KU. GUPTAPIYUSH KU. GUPTA NOGESHWAR KU. NOGESHWAR KU.

DEWANGANDEWANGAN

RUNGTA COLLEGE OF ENGG. & TECHNOLOGY

CONTENTCONTENT

Introduction.Introduction. Power flow in HVDC transmission.Power flow in HVDC transmission. Why use DC transmission?Why use DC transmission? Comparison between AC & DC transmission.Comparison between AC & DC transmission. Cost & power.Cost & power. Advantages and disadvantages.Advantages and disadvantages. Application of HVDC transmission.Application of HVDC transmission.

IntroductionIntroduction

Electrical power transmission was done with direct Electrical power transmission was done with direct current.current.

In 1950, a 116 km experimental transmission line In 1950, a 116 km experimental transmission line was commissioned from Moscow to Kasira at 200 was commissioned from Moscow to Kasira at 200 kV.kV.

The first commercial HVDC line built in 1954 was a The first commercial HVDC line built in 1954 was a 98 km submarine cable with ground return 98 km submarine cable with ground return between the island of Gotland and the Swedish between the island of Gotland and the Swedish mainland mainland

Today, the highest functional d.c. voltage for d.c. Today, the highest functional d.c. voltage for d.c. transmission is +/- 600 kV for the 785 km transmission is +/- 600 kV for the 785 km transmission line of the Itaipu scheme in Brazil.transmission line of the Itaipu scheme in Brazil.

Power flow in HVDC Power flow in HVDC transmissiontransmission

G - GeneratorG - Generator T1,T2 - TransformerT1,T2 - Transformer R - RectifierR - Rectifier I - InverterI - Inverter

G R I

T1 T2

LOAD

Why use DC transmission?Why use DC transmission?

Losses are lower.Losses are lower. Towers can be designed to be less costly per unit Towers can be designed to be less costly per unit

of length.of length. Lower visual profile.Lower visual profile. Transmission is by underground cable.Transmission is by underground cable. Power systems are not synchronized to Power systems are not synchronized to

neighboring networks due to frequency.neighboring networks due to frequency.

Comparison between AC & DC Comparison between AC & DC transmissiontransmission

Economics of transmissionEconomics of transmissionI.I. Carry much power in DC w.r.to ACCarry much power in DC w.r.to AC..

II.II. Losses reduce due to skin & corona effectLosses reduce due to skin & corona effect . .

Technical PerformanceTechnical Performance I.I. Full control over power transmittedFull control over power transmitted..

II.II. Fast control to limit fault current in DC linesFast control to limit fault current in DC lines

ReliabilityReliability I.I. HVDC links in the world is available.HVDC links in the world is available.

II.II. Thyristor valves is much more reliable than Thyristor valves is much more reliable than mercury arc valves.mercury arc valves.

Cost & powerCost & power

d*= break-even distanced*= break-even distance

POWER

DISTANCEDISTANCE

COSTS

AC

DC

d*

DCAC

Variation of cost with line length

Power transfer capability vs. transfer

Advantages and Advantages and disadvantagesdisadvantages

Disadvantages of DC transmission Disadvantages of DC transmission The difficulty of breaking DC currents which results in high cost The difficulty of breaking DC currents which results in high cost

of DC breakers .of DC breakers . Inability to use transformers to change voltage levels.Inability to use transformers to change voltage levels. High cost of conversion equipment.High cost of conversion equipment. Generation of harmonics which require AC and DC filters, Generation of harmonics which require AC and DC filters,

adding to the cost of converter stations.adding to the cost of converter stations. Complexity of control.Complexity of control.

But today's DC technology, which have tried to But today's DC technology, which have tried to overcome the disadvantages. overcome the disadvantages.

Development of DC breakers.Development of DC breakers. Modular construction of thyristor valves.Modular construction of thyristor valves. Increase in the ratings of thyristor cell that make up a valve.Increase in the ratings of thyristor cell that make up a valve. Twelve pulse operation of converters.Twelve pulse operation of converters. Use of metal oxide, gapless arrestors.Use of metal oxide, gapless arrestors. Application of digital electronics and fiber optics in control of Application of digital electronics and fiber optics in control of converters. converters.

Application of HVDC Application of HVDC transmissiontransmission

Long distance bulk power transmission.Long distance bulk power transmission. Underwater or underground cables. Underwater or underground cables. Control and stabilization of power flows in AC ties in an Control and stabilization of power flows in AC ties in an

integrated power system.integrated power system. Asynchronous interconnection of AC systems operating at Asynchronous interconnection of AC systems operating at

different frequencies or where independent control of different frequencies or where independent control of system is desired. system is desired.

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HVDC