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HVDC

TRANSMISSION

H-HIGH

V-VOLTAGE

D-DIRECT

C-CURRENT

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ANEY EXECUTIVE ENIGINEER+ 500KV HVDC TERMINAL STATIONMSETCL CHANDRAPUR

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SINGLE LINE DIAGRAM AC YARD,CHANDRAPUR

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SINGLE LINE DIAGRAM DC YARD,CHANDRAPUR

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MONOPOLAR GROUND CONNECTION

BIPOLAR CONNECTION

TYPES OF CONNECTIONS OF HVDC CONVERTER BRIDGE

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BACK -TO-BACK This is application where two AC systems to beconnected are physically in same substation and notransmission line or cable is required.This is used forinterconnection between asynchronous Power Systemnetworks.

TRANSMISSIONBETWEEN TWOSUBSTATION.

This is for bulk power transfer through dc line or cablefrom one Substation to another which aregeographically far away from each other.

MULTITERMINALSYSTEM

More than two HVDC Substation, geographicallyseparated are connected to each other by sametransmission line then it is multiterminal system.

PARALLELMULTITERMINALSYSTEM

If one or more converters are connected at same voltagelevel then system is parallel multiterminal.Here voltageremains same but the current capacity increases.

SERIESMULTITERMINALSYSTEM

If one or more converters are connected in series thensystem is series multiterminal.Here voltage increases.

UNIT CONNECTION This is scheme when generator is directly connected tothe converter transformer of the rectifier so thatgenerated power is directly fed into dc line

Different types HVDC Converter Bridge Arrangements

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MONOPOLAR METALLIC RETURN

6

RECTIFIER INVERTER

RECTIFIER INVERTER

POLE-1

POLE-2

MRTB

RECTIFIER INVERTER

RECTIFIER INVERTER

POLE-1

POLE-2

MRTB

GRTS

GRTS

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TWO TERMINAL HVDC

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PRINCIPLE OF POWER TRANSFER BETWEEN TWO CONVERTER STATIONS

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I=(V1-V2)/R

V1 V2

RECTIFIER INVERTER

TRANSMISSION LINERESISTANCE (R)

CURRENT(I)

P=V2*I

10V 9V

RECTIFIER INVERTER

TRANSMISSION LINERESISTANCE(R=1OHMS)

CURRENT(I)

I=(10-9)/1=1AMP

P=9*1=9W

12 9V

RECTIFIER INVERTER

TRANSMISSION LINERESISTANCE(R=1OHMS)

CURRENT

(I)

I=(12-9)/1=3AMPP=9*3=27W

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Static Ud/Id Characterstics

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Io(rectifier)Io(inverter)

Current Margin

DC Voltage

DC Current

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12 pulse bridge with three phase transformer connected

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DCCT

DCCT

To controlsystem

Tocontrolsystem

DC voltagedivider

DC voltagedivider

Smoothingreactor

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12 PULSE CONVERTER

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CHANDRAPUR PADHE HVDC

PROJECT

FEATURES:A. BIPOLE PROJECT

B. TRANSMISSION VOLTAGE 500KVC. POWER CARRYING CAPACITY 1500 MW OR 750MW

/POLE.D. OVERLOAD CAPACITY :

1650 MW FOR 2HRS AMBIENT ABOVE 33 C .2200 MW FOR 5 SECS AMBIENT BELOW 33C .

E. TYPE OF THRISTOR VALVE QUARAPULE VALVE.F. TYPE OF CONDUCTOR -QUARAPULE

CONDUCTOR/POLE.G. NO.OF FILTERS/STATION-4NOS.H. FILTER MVAR CAPACITY /STATION-800MVAR.

I. LINE LENGTH 753 KM.J. INTERSTATION COMMUNICATION AND

COMMUNICATION BETWEEN LD,KALWA THROUGHOPTICAL FIBRE

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RATING OFLINK

PowerTransmis

sionCapability (MW)

MinimumContinuousRating

1500

NominalRating 1500

2 hours

overloadrating 1650

CHA-PAD HVDC

+/- 500KV, 1500MW CHANDRAPUR PADGHE BIPOLE HVDC PROJECT

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AC SIDE VALVE HALL DC SIDE

A) AC FILTERS A)THYRISTOR VALVES A)DC FILTERS

B) CONVERTERBREAKERS

B)DC BUS ARRESTORS B)DC BREAKER(METALLIC RETURNTRANSFER BREAKER,GROUND RETURNTRANSFERSWITCH,NEUTRAL BUSSWITCH)

C) MEASURINGEQUIPMENTS

C)VALVE COOLINGSYSTEM

C) SMOOTHINGREACTOR

D) CONVERTERTRANSFORMERS

D)DC CTs, DC VOLTAGEDIVIDERS.

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CONVERTERTRANSFORMER

AC SIDE

DC SIDE

VALVEHALL

CONVERTERBREAKER

AC FILTER

DC BUSARRESTOR

D C

F I L T E R

DC VOLTAGEDIVIDER

DC CT

DC LINEISOLATOR

NBS

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AC SIDE EQUIPMENTSAC Side mainly Constitutes of1)Ac filters: They serve two purposeA) They offer low impedance path to the harmonics which travel on AC side

generated during the conversion process.B)Filters constitutes of R,L&C .These filter caters part of capacitive MVAR to the ACBus which helps in boosting the system voltage.

Harmonics Generated are:i)Harmonics of the order of h=2 to 5 due to voltage imbalance caused by firing

angle and transformer commutation inductance.ii)h=pq1 order Harmonics are generated on AC side of Converter where p is a

value dependent on 6 or 12 pulse Bridge and n=1,2,

Switching of the Ac filters through Circuits Breakers are done byReactive Voltage Controller depending on the DC power flow throughthe link.

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U

(a) (b) (c)Single Tuned Filter Double Tuned Filter

HP-12 HP-3 HP-24/36

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AC FILTER BANK

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AC SIDE EQUIPMENTS

2) Converter breakers: Breakers generally SF6 are used for catering ACsupply to the Converter Transformer. In Bipolar Projects sometimes

it is required that only one Converter Breaker caters load to bothpoles depending on the type of Bus bar arrangements .In such casesConverter Breakers of high current carrying capacity are employed s.Also Circuit Breakers are employed for Switching in and out of theAC Filters.

3) Measuring Equipments: Equipments like CVTs are installed formeasurement of bus voltages which useful in for control of poweron HVDC link. CTs installed in AC yard as well as Filter area areemployed for protection of AC Bus and Filters respectively.

4) Converter Transformers: This is one of the key equipments in HVDClink.AC supply is fed to the Converter through the transformer .Asthe name suggests the transformer is connected to the converter.

The secondary or the valve winding of the Transformer is directlyconnected to valve through either wall mounted bushing or thebushings of the transformer are protruding inside the valve hall andare connected to the valve. The secondary of the convertertransformer is carrying AC as well as DC valve current through it. Thetransformers may be of following type in case of 12- pulseconverters:-

i) 1phase 3 winding transformer 3units/pole.

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CONVERTER TRANSFORMER

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.

3A

3B

A

B1 B2

2A

2B

1PHASE THREE WINDING CONVERTER TRANSFORMER

PRIMARYWINDING

SECONDARYWINDING 1

SECONDARYWINDING 2

.

.

.

....

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CONVERTER TRANSFORMER

12 -PULSE CONVERTER FED BY THREE PHASE TRANSFORMER

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VALVE HALL EQUIPMENTS1) Thyristor Valves: Thyristor valves are heart of HVDC .These valves

are air insulated , water cooled and suspended in controlledenviroment. Previously the thyristor valves where erected on

ground but nowadays they are suspended to meet the seismicrequirements. The 12-pulse bridge consist of 3 nos. quadruple valve.Each quadruple valve is connected to one phase. One valve consistsof no. of thyristors connected in series depending on the rating ofthe thyristor. Each thyristor is equipped with damping circuit fordv/dt protection, series connected reactor for di/dt protection forgroup of thyristor and thyristor control unit for the firing as well as

for status monitoring of thyristor .

Configuration for Chandrapur Padghe project: 3 nos. Quadruple valve 1 valve consist of 16 modules 1 module consist of 6 thyristors 1 valve consist of 96 thyristors Each phase quadruple valve consist of 384 thyristor One pole converter consist of 1152 thyristor Series connected thyristor Fine Water cooled valves. Each thyristor of blocking voltage 7kv ,1700amp DC.

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Single Thyrister

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Thyrister Module

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Thyrister Module

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Quadruple Converter Valves

Quadruplevalve

Double valve

Single valve

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VALVE HALL EQUIPMENTS2) Fine Water Cooling system For Converter Valves:

Dissipation of losses in the form of heat from ThyristorValves.Fine water / Demineralised water used for heat dissipation.Few percent of water routed through water treatment

circuit.Temperature, Conductivity and leakage is monitored. 31

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DC SIDE EQUIPMENTSC Side mainly constitutes:DC Smoothing Reactor: Smoothing Reactor is the first equipment connectedseries on DC side i.e. HV side .As the name suggest it is for Smooth ripple free

C and also limits the sudden change in DC current during fault on DC line or DCus. The reactor are generally air insulated or oil filled smoothing reactor. At lowC voltage air insulated smoothing reactor are used but for high voltage oilsulated smoothing reactor is used.

pecification of Smoothing reactors in Chapad Project:nductance (L): 350mH

Rated Voltage : 500KV DCRated current 1700 amp DC

DC filters:- The harmonics generated on DC side are of the order of h=knhere k=6 or 12 depending on the type of converter 6 or 12 pulse. Thesermonics result in current harmonic in DC line. As no. of harmonics increasese amplitude of the harmonics decreases.

DC Switches/Breakers :- DC side Switches are basically High speed isolatorhich connect the neutral bus to earth electrode line or metallic return path oration ground .They divert/isolate the dc current in event of any fault on DCde. They do not perform the function of current breaking. There are 4 types ofC Switches:. NBS.NBGS. MRTB.GRTB

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DC SIDE EQUIPMENT) Neutral Bus Switch (NBS): This DC Switch performs the function of connectinge the converter to the neutral bus. In event of any fault on the neutral bus theBS isolates the neutral bus and the converter after the operation of respectiveotection.Neutral Bus Grounding Switch (NBGS): This Switch provides path for local /

ation grounding in event of breakdown on electrode line or any maintenancen electrode line or on Metallic return transfer breaker during bipolar balancedndition .Metallic return transfer Breaker (MRTB):- This Switch is used to commutatee current from ground return path to metallic return path. In this type ofansfer .The current that is commutated from Ground path to metallic path isar about 70 t0 80 percent of pole current due to difference in the resistancefered by these two paths. Hence Special Arrangement is adopted for current

uenching from Ground to metallic path which shown in figure) Ground return transfer Switch (GRTS) : The GRTS is used to commutaterrent from metallic return to ground return The maximum DC current that is tocommutated in this case is only 20 to 30 percent.

BREAKERCONTACTS

SPARK GAP

CAPACITOR

NON-LINEAR

RESISTOR