HVDC AND LINKS

BY:G.MOHAMMED MUSTAFA EEE-THIRD-YEAR DHAANISH AHMED OF COLLEGE

OF ENGG.

INTRODUCTION

HVDC Stands for High Voltage Direct Current and is today a well-proven technology employed for power transmission all over the world.

HVDC technology is used to transmit electricity over long distances by overhead transmission lines or submarine cables.

It is also used to interconnect separate power systems,where traditional alternating current(AC) connections can not be used.

Different Categories of HVDC Transmissions

Non-synchronous Submarine cableLong-distanceOverhead linesUnderground cable

HVDC System Configuration

HVDC links can be broadly classifield into:

Monopolar linksBipolar linksHomopolar links

Monopolar Links

It uses one conductorThe return path is provided by ground or waterUse of this system is mainly due to cost considerations.A Mettalic return may be used where earth resistivity is too high.This configuration type is the first step towards a bipolar link

Bipolar Links

Each terminal has two converters of equal rated voltage ,connected in series on the DC sideThe junctions between the converters is groundedIf one pole is isolated due to fault,the other pole can operate with ground and carry half the rated load.

Homopolar Links

It has two or more conductors all having the same polarity,usually negative.Since the corona effect in DC transmission lines is less for negative polarity,homopolar link is usually operated with negative polarityThe return path for such a system is through ground.

Components of HVDC Transmission Systems

ConvertersSmoothing reactorsHarmonic filtersReactive power suppliesElectrodesDC lines AC circuit breakers

Control of HVDC systems

Objectives of Control• Efficient and stable operation .• Maximum flexibility of power control without

compromising the safety of equipment.• Principle of operation of various control

systems.• Implementation and their performance during

normal and abnormal system conditions.

WHY TO PREFER HVDC THAN HVAC?

Long distance transmissionFive times more energy transmits than ACLess losses(no inductance,capacitance)Cost of transmission medium & land is lowMaintenance & operation cost is lowIntial cost is high but overall cost is low than

AC

HVDC Vs HVAC

Comparison between the prices and losses of AC &DC Transmission

Advantages

Technical Reactive power

requirement. Short circuit current. Independent control of

ac system. Fast change of energy

flow. Greater reliability.

Economical 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 dc lines are lesser tha ac lines.

Disadvantages

The disadvantages of HVDC are in conversion,switching and control.

Expensive inverters with limited overload capacity.

Higher losses in static inverters at smaller transmission distances .

The cost of the inverters may not be offset by reductions in line construction cost and lower line loss.

Conclusion

HVDC is very important issue in transmission energy.

Problem of cascade blackout,can be reduced by application of HVDC.

The data collected from 31 utilities says that forced unavailability of energy due to the converter station is 1.72percent.

The scheduled unavailability of energy is about five percent.

QUERIES????

THANK YOU

PRESENTED BY:G.MOHAMMEDMUSTAFA

EEE-THIRD-YEARDHAANISH AHMED COOLEGE OF ENGG.