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.