1. Page 1 05.08.2014
PRESENTATION ON HIGH
VOLTAGE DIRECT CURRENT
(HVDC) SYSTEM
Mohammed Azadar Naqvi
Summer Training in BHEL
Under Supervision of Mr. M I Khan
2. Page 2 05.08.2014
2300
Indian Power Scenario
Installed Capacity : 1,25,000 MW
Peak Demand : 92,000 MW
Peak Availability : 82,000 MW
Energy growth : 8-9% / annum
34,280 MW
35240 MW
16680
35,800 MW
2440
Surplus Regions
Deficit Regions
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Energy Resources
confined mostly to ER
and NER
Target beneficiaries are
mostly in WR and NR
Uneven Disposition of Energy
Resource
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Advantages of HVDC
Why HVDC rather than HVAC?
Long distances make HVDC cheaper
Improved link stability
Fault isolation
Asynchronous link
Right-of-way for an AC Line designed
to carry 2,000 MW is more than 70%
wider than the right-of-way for a DC
line of equivalent capacity.
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• The need to convert to and from AC implies the terminal
stations for a DC line cost more.
• There are extra losses in DC/AC conversion relative to AC
voltage transformation.
• Operation and maintenance costs are lower for an
optimized HVDC than for an equal capacity optimized AC
system.
• The cost advantage of HVDC increases with the length, but
decreases with the capacity, of a link.
• For both AC and DC, design characteristics trade-off fixed
and variable costs, but losses are lower on the optimized DC
link.
AC versus DC
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Cost comparison of ac and
dc transmission
Cost of DC terminal
Cost of AC terminal
Cost
Break even distance
Distance
Cost of AC Line
Cost of DC Line
≈ 500 – 700 km
Break even point indicates where lower cost of HVAC transmission crosses
the upper cost of HVDC link. Two line indicate the cost with ±10%.
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96 m 46 m
400 kV AC Lines ±500 kV DC Line
Comparison of right of way
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Typical tower structures
and rights-of-way for
alternative transmission
systems of 2,000 MW
capacity.
Comparison of right of way
(continued)
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For equivalent transmission capacity, a DC line has lower
construction costs than an AC line
A double HVAC three-phase circuit with 6 conductors is
needed to get the reliability of a two-pole DC link.
For the same conductor, DC losses are less, so other
costs, and generally final losses too, can be reduced.
Relative Cost of AC versus DC
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HVDC is particularly suited to undersea transmission,
where the losses from AC are large.
First commercial HVDC link (Gotland 1 Sweden, in 1954)
was an undersea one.
Back-to-back converters are used to connect two AC
systems with different frequencies –two regions where AC is
not synchronized – as in India
Special Applications of HVDC
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HVDC links can stabilize AC system frequencies and
voltages, and help with unplanned outages.
A DC link is asynchronous, and the conversion stations
include frequency control functions.
Changing DC power flow rapidly and independently of AC
flows can help control reactive power.
HVDC links designed to carry a maximum load cannot be
overloaded by outage of parallel AC lines.
Special Application (continued)
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Present HVDC Installation
Vindhyachal:2x250 MW June 89
Chandrapur 2x500 MWApril 97
Vizag I 1x500 MW, Sept 99
Sasaram 1x500 MW, Sept 02
Vizag II 1x500 MW, March 05
Rihand-Dadri: ± 500 kV, 1500 MW, Dec 90
Chandrapur-Padghe:±500,kV,1500MW, 1999
Talcher-Kolar :± 500 kV, 2000 MW, Sept 02
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13 Ohm
800 kV
775.6 kV
1875 A
1 Ohm
10 V
9.0 V
1 A
FUNDAMENTAL OF HVDC
OPERATION
19. Page 19 05.08.2014
Basic HVDC Single Line Diagram
DC OH Line
Converter
Transformer
DC Filter:
DT 12/24
DT 12/36
DC Filter:
DT 12/24
DT 12/36
Thyristor
Valves
400 kV
AC Bus
AC Filters,
Reactors
Smoothing Reactor
Converter
Transformer
DC Filter:
DT 12/24
DT 12/36
DC Filter:
DT 12/24
DT 12/36
Thyristor
Valves
400 kV
AC Bus
AC Filters
Smoothing Reactor
22. Page 22 05.08.2014
DC OH Line
Converter
Transformer
Thyristor
Valves
400 kV
AC Bus
AC Filters,
Reactors
Smoothing Reactor
Converter
Transformer
Thyristor
Valves
400 kV
AC Bus
AC Filters
Smoothing Reactor
Current
Current
Mode of Operation (Continued)
23. Page 23 05.08.2014
Mode of Operation (Continued)
DC OH Line
Converter
Transformer
Thyristor
Valves
400 kV
AC Bus
AC Filters,
Reactors
Smoothing Reactor
Converter
Transformer
Thyristor
Valves
400 kV
AC Bus
AC Filters
Smoothing Reactor
Current
Current
Under one pole outage, automatic changeover to MetallicUnder one pole outage, automatic changeover to Metallic
return with transmission capacity of healthy pole in less than 40sreturn with transmission capacity of healthy pole in less than 40s
24. Page 24 05.08.2014
DC OH Line
Converter
Transformer
Thyristor
Valves
400 kV
AC Bus
AC Filters,
Reactors
Smoothing Reactor
Converter
Transformer
Thyristor
Valves
400 kV
AC Bus
AC Filters
Smoothing Reactor
Mode of Operation (Continued)
Current
Current
Under one pole outage, automatic changeover to GroundUnder one pole outage, automatic changeover to Ground
return with transmission capacity of healthy pole in less than 60sreturn with transmission capacity of healthy pole in less than 60s
