Baby

1. HVDC
Transmission

2. Challenges
withAC
PowerLines
AClinesbecomeloadedclosertotheirthermal
capacitywithincreasinglosses.
Reducedpowerqualitycausestheriskofdeclining
networkstability.
Overhead lineschangethelandscape,causespublic
resentment.
LimitthedistanceoftraditionalACunderground
cablestoaround80km.

3. Solution:
HVDC
technology
HVDCtechnologyhasthepotentialtoplayan
importantroleinachievingthis solution.
It providesimproved power quality and power
ow control as well.
Introducing extrudedDC-cableswhich haveno
technicallimitto distancewhichcan beinstalled.
Itcan provide an alternative to overheadlines
particularlywhenthe totalcapitaland
environmentalcostsareconsidered.

4. HVDC-
Introduction
HVDC(high-voltagedirectcurrent) isahighly
e cientalternativefortransmittinglargeamounts
ofelectricityoverlongdistancesandforspecial
purposeapplications.
Comparedtoalternatingcurrent,thedirectcurrent
systemislessexpensiveandloseslessenergy.
HVDCcanbetransmittedthroughcablesboth
undergroundandunderwater.

5. Advantages
AdvantagesofHVDC
Technical
Advantages
Economic
Advantages

6. Technical
Advantages
Reactivepowerrequirement
Systemstability
ShortCircuitCurrent
IndependentControlofacsystem
Fastchangeofenergy ow
LesserCoronaLossandRadiointerference
GreaterReliability.
Directionofpower ow canbechangedveryquickly
LargeHVDCschemes(5000MW-6400MW) are
usedtoaccessremotehydropowerresources,hence
renewableenergywithnoCO2 emissions.
HVDCismoreeconomicalthanHVACforschemes
withtransmissiondistancesmorethan700km.

7. Economic
Advantages
DClinesandcablesarecheaperthanAClinesor
cables.
ThetowersoftheDClinesarenarrower,simpler
andcheapercomparedtothetowers oftheAC
lines.
LinelossesinaDClinearelowerthanthelosses
inanAClines.

8. Thediagramshowsa
comparisonofthelossesin1,
200MWoverheadline
transmissionsusingACand
HVDC.
LowerLosses

9. LowerInvestmentCost
•
•
ItistruethatHVDC
terminalstationsare
moreexpensivedueto
thefactthattheymust
performtheconversion
fromACtoDC,andDCto
AC.
Butoveracertain
distance,thesocalled"
break-evendistance"
(approx.600–800km),
theHVDCalternativewill
alwaysprovidethe

10. How doesit
work?
HVDCtransmissionutilizesaconverterstationat
eitherendofthesystem.
Amercuryarcvalveorsolidstatevalve(thyristor)
isusedfortheconversionofACandDCcurrent.
Thevalveatthebeginningofthesystemconverts
alternatingcurrenttoHVDC,theHVDCtravelsto
thenextlocationthroughacable.
Thevalveattheendofthesystemconvertsthe
HVDCbacktoalternatingcurrent.

11. Wind Power AC Transmission
Line
AC toDC
Converte
rStation
HVDC
Transmissio
n Line
DC toAC
Converte
rStation
AC Transmission
Line
Distribution
Line
HVDCtransmissionsystem

12. Components
ofanHVDC
transmission
system

13. Transmission
Medium
Forbulkpowertransmissionoverland,themost
frequenttransmissionmediumusedistheoverheadline.
Thisoverheadlineisnormallybipolar,i.e.two
conductorswithdi erentpolarity.
HVDCcablesarenormallyusedforsubmarine
transmission.
Themostcommontypesofcablesarethesolidand
theoil- lledones.
HVDCundergroundorsubmarinepowertransmissions:
Thisnew HVDCcableismadeofextruded
polyethylene,andisusedinVSCbasedHVDC
systems.

14. Typesof
HVDC
con guratio
ns
H
V
D
C
c
o
n
g
u
r
a
t
i
o
n
s
Monopole
Bipolar
Backtoback
Multi-terminal
systems
Tripole

15. Monopolar
Link
Oneoftheterminaloftheconverterisconnected
tothetransmissionline,whiletheotherterminalis
connectedtotheground.
Thegroundisusedasareturnpathhere.
AlsoMonopolarlinkcanbeusedtotransmit
poweroverseabyusingspecialelectrodeforthe
earthreturn.

16. BipolarLink
Therearetwopole/conductors.Oneoperatesat
positivepolarityandotherisonnegativepolarity.
TheBipolarlinkseemstobecostlierthanMonopolar,
butitismorereliablethanMonopolar.
Theadvantageofbipolaristhatwheneveroneofthe
polesfails;thesystemoperatesasMonopolarlinkwith
thegroundasreturnpath.

17. Multi
terminalLink
AMultiterminalHVDCsystemisusedtoconnectwith
morethantwoconverterstations.
complexnetworkascomparedtoMonopoleand
BipolarHVDClink.
Thereversalofpowercanbeeasilyachievedusingthe
MultiterminalHVDClink.

18. BacktoBack
(B2B)
Used to connect the asynchronous systemwith di erent
frequencies.
The length ofthe back to back connection is kept very
small.
Sometimes it may vary depending on the system
requirement.
Helps to achieve the connection between any
asynchronous systems.

19. Tripole
Twoofthethreecircuitconductorsareoperatedasa
bipole.
Thethirdconductorisusedasaparallelmonopole,
equippedwithreversingvalves(orparallelvalves
connectedinreversepolarity).
Theparallelmonopoleperiodicallyrelievescurrent
fromonepoleortheother,switchingpolarityovera
spanofseveralminutes.
Asof2012,notri-poleconversionsareinoperation.

20. Converter
Station
Equipment
Thyristorvalves
ConverterTransformer
DCReactor
Harmonics Filtering Equipment
ControlEquipment
Reactivepowercompensation

21. Ground
Return
Mostdctransmissionlinesusegroundreturnfor
reasonsofeconomyandreliability.
Groundreturnareusedbythemonopolarandthe
bipolarlinkforcarryingthereturncurrent.
Thegroundpathhasalow resistanceand,therefore
low powerlossascomparedtoametallicconductor
pathprovidedthegroundelectrodesareproperly
designed.
Theresistanceofthegroundpathisindependentof
thedepthoftheline.

22. Earth
Electrode
HVDCsystemrequiresaproperlydesignedearth
electrodeateachstation.
Theelectrodeissituatedatasafedistance(5to30
km) fromthestation.
Theearthelectrodeatoneofthestationactsasa
anodeandattheotherendactsasacathode.

23. Disadvantag
es
Thedisadvantagesof HVDCarein conversion,switching,control,
availabilityandmaintenance.
HVDCislessreliableandhasloweravailabilitythan alternating
current(AC)systems,mainlyduetotheextraconversion
equipment.
Therequiredconverterstationsareexpensiveandhavelimited
overloadcapacity.
Atsmallertransmission distances,thelossesin theconverter
stationsmaybebiggerthan in an ACtransmission lineforthe
samedistance.
OperatingaHVDCschemerequiresmanysparepartstobekept,
often exclusivelyforonesystem,asHVDCsystemsareless
standardizedthan ACsystemsandtechnologychangesfaster.

24. Conclusion
HVDCo ers powerfulalternativetoincrease
stabilityofa powersystem as wellas to
improvesystem operating exibilityand loss
reduction.

25. ThankYou