Introduction in High voltage dc you are HVDC stands for High Voltage Direct Current. It's a technology used for transmitting electricity over long distances with lower energy losses compared to traditional AC (Alternating Current) transmission systems. HVDC systems are often used for interconnecting power grids, transmitting power from remote renewable energy sources, and improving grid stability. They involve converting AC to DC at the sending end, transmitting the power via cables or overhead lines, and then converting it back to AC at the receiving end. HVDC stands for High Voltage Direct Current. It's a technology used for transmitting electricity over long distances with lower energy losses compared to traditional AC (Alternating Current) transmission systems. HVDC systems are often used for interconnecting power grids, transmitting power from remote renewable energy sources, and improving grid stability. They involve converting AC to DC at the sending end, transmitting the power via cables or overhead lines, and then converting it back to AC at the receiving end.

1. EEU725A HVDC AND FACTS
• Introduction to HVDC:
• Introduction of DC Power transmission technology – Comparison of
AC and DC transmission, Application and Description of DC
transmission system, Planning for HVDC transmission, Modern
trends in DC transmission, Types of HVDC Systems.
• Analysis of HVDC Converters:
• Pulse Number-Choice of converter configuration, simplified
analysis of Gratez circuit, 12- pulse converter based HVDC systems
and their characteristics, Control of Converters.
• Harmonics and Filters:
• Introduction – Generation of Harmonics, Design of AC filters and
DC filters, HVDC light and HVDC PLUS (Power Universal Link), Series
and Parallel operation of converters.
•

2. EEU725A HVDC AND FACTS
• Introduction to FACTS:
• The concept of flexible AC transmission – reactive power control in
electrical power transmission lines, uncompensated transmission
line, Introduction to FACTS devices and its importance in
transmission Network, Introduction to basic types of FACTS
controllers, Comparison of HVDC and FACTS.
• FACTS Controllers:
• Principles of series and shunt compensation, description of static
var compensators (SVC), thyristor controlled series compensators
(TCSC), static phase shifters (SPS), static synchronous series
compensator (SSSC), STATCOM.

3. The history of the evolution of electric power system
• The commercial use of electricity began in the late 1870s when arc lamps
were used for lighthouse illumination and street lighting.
• First Complete Electric Power System – 1882
• The first complete electric power system (comprising a generator, cable,
fuse, meter, and loads) was built by Thomas Alva Edison – the historic
Pearl Street Station in New York City which began operation in September
1882.
• This was a dc system consisting of a steam-engine-driven dc
generator supplying power to 59 customers
within an area roughly 1.5 km in radius.
• The load, which consisted entirely of
incandescent lamps, was supplied at
• 110 V through an underground cable system.

4. Introduction of AC Systems – 1886
• In spite of the initial widespread use of dc systems, they were
almost completely superseded by ac systems. By 1886, the
limitations of dc systems were becoming increasingly
apparent. They could deliver power only a short distance from
the generators.
• To keep transmission power losses and voltage drops to
acceptable levels, voltage levels had to be high for long-
distance power transmission. Such high voltages were not
acceptable for generation and consumption of power;
therefore, a convenient means for voltage transformation
became a necessity.
• The development of the transformer and ac transmission by L.
Gaulard and J.D. Gibbs of Paris, France, led to ac electric
power systems. George Westinghouse secured rights to these
developments in the United States.

5. • In 1886, William Stanley, an associate of Westinghouse,
developed and tested a commercially
practical transformer and ac distribution system for 150 lamps
at Great Barrington, Massachusetts.
With the development of polyphase systems by Nikola Tesla,
the ac system became even more attractive.
• By 1888, Tesla held several patents on ac
motors, generators, transformers, and transmission systems.
Westinghouse bought the patents to these early inventions,
and they formed the basis of the present-day ac systems.
• AC vs DC [Tesla vs Edison]
• In the 1890s, there was considerable controversy over
whether the electric utility industry should be standardized on
dc or ac.
• There were passionate arguments between Edison, who
advocated dc, and Westinghouse, who favoured ac.
•

6. • This posed a problem for interconnection. Eventually 60 Hz was adopted
as standard in North America, although many other countries use 50 Hz.
• The increasing need for transmitting larger amounts of power over longer
distances created an incentive to use progressively higher voltage levels.
• Early AC Systems
• The early ac systems used 12, 44, and 60 kV (RMS line-to-line).
• This rose to 165 kV in 1922, 220 1W in 1923, 287 kV in 1935, 330 kV in
1953, and 500 kV in 1965.
• Hydro Quebec energized its first 735 kV in 1966, and 765 kV was
introduced in the United States in 1969.
• To avoid the proliferation of an unlimited number of voltages, the industry
has standardized voltage levels.
• The standards are 115, 138, 161, and 230 kV for the high voltage (HV)
class, and 345, 500 and 765 kV for the extra-high voltage (EHV) class.

7. The limitation of HVAC transmission
system
• Reactive Power Loss: ...
• Stability: ...
• Current Carrying Capacity: ...
• Skin and Ferranti Effect:
• Power Flow Control is not Possible: ...
• Requires less space compared to ac for same voltage rating and size. ...
• Ground Can be used as return conductor. ...
• Less corona loss and radio interference.

8. Constraints of AC Transmission
P
distance
Thermal Limit of conductors
DC Line
AC line
Voltage and
Stability Constraints
SIL
CONSTRAINTS FOR LONG DISTANCE TRANSMISSION

9. SIL -Surge Impedance Loading is the connected load in transmission line for
which reactive power generated is equal to reactive power consumed i.e. the
flow of reactive power is zero. There is an exact balance between reactive power
generation and consumption
Surge Impedance Loading is a very essential parameter when it comes to
the study of power systems as it is used in the prediction of maximum loading
capacity of transmission lines.
following equation
Capacitive VAR = Inductive VAR
V2
Where,
V = Phase voltage
I = Line Current
Xc = Capacitive reactance per phase
XL = Inductive reactance per phase
Upon simplifying
Where,f = Frequency of the system L = Inductance per unit length of the
line l = Length of the line Hence we get, V/I=Sq Root L/C=Zs

10. • Reactive Power Loss:-
inductances and the capacitance in the transmission lines and
also there are so, many elements that is, corresponding to the
reactive power loss will be one of the concern in AC system.
• The Ferranti effect
if the system is system is lightly loaded or unloaded then
receiving end voltage is higher than the sending end voltage, to
control the Ferranti effect We normally use the reactors. We
have the three types of reactors one is your line reactors, bus
reactors and the tertiary reactors,
• Skin effect
• if the two conductors are there and the AC current is flowing.
So, due to the effect of current and flux in first coil it will be
affecting another coil and thereby; it will change the
reactance and the impedance of the line.

11. • The power flow control;
• the actual AC system, it is not possible to control, it depends upon
the current will follow depending upon the impedance seen by the
current
• Stability the stability is one of the concerns in your AC system, if
your system is highly loaded though that system is more prone to
the instability.
• Current carrying capability
1. cannot have long cables or long transmission lines due to the
huge charging, and especially in the extra high voltage system
2. cannot load the line fully to their thermal limit,
3. cannot have a longer distance cable.
( Due to the excessive charging it is not possible to have a long
distance cable and so, that we have to go for the DC cables in that
cases the skin effect and the Ferranti effect is also prominent in
the AC).

12. Why HVDC ?
• Direct current : Roll
along the line ;
opposing force
friction (electrical
resistance )
• AC current will
struggle against
inertia in the line
(100times/sec)-
current inertia –
inductance-reactive
power

13. Major advantage of HVDC
In the HVDC transmission system all these four problems
are eliminated, and that becomes advantage of the DC
transmission system means,
• There is no reactive power loss at all as reactive L and C has
no impact on that then
• There is no stability concern, because there is no Power
angle delta.
•The stability concern does not arise and thereby we can
load our transmission lines up to it is thermal limit.

14. Lower losses explained
~
AC Load
Generator
L L L L
R R R R
C C C
Inductors (L) counteract changes of the line current  Inductive losses
Capacitors (C) counteract changes of the line voltage  Capacitive losses
Current and voltage changes polarity 50 or 60 times per second !
Resistors cause resistive losses and can not be avoided
DC =
Direct Current flows without any changes in Current and Voltage
thereby eliminating the Reactive Losses
The ideal world
Reality
Transmission line equivalent, simplified

15. HVDC Transmission Systems – 1950s
• With the development of mercury arc valves in the
early 1950s, high voltage dc (HVDC) transmission
systems became economical in special situations.
• The HVDC transmission is attractive for transmission
of large blocks of power over long distances. The
cross-over point beyond which dc transmission may
become a competitive alternative to ac transmission
is around 500 km for overhead lines and 50 km
for underground or submarine cables.

16. HVDC Transmission System
DC generation has problem of commutation and insulation, so HVDC
cannot be generate. Also, voltage transformation is not possible with ease
and efficiency in DC by transformer like device.
In AC form electricity can be
generated and step up by
transformers. For HVDC transmission
it is converted into DC with the help
of rectifier.
The DC power will flow through the
overhead lines. At the user end, this
DC has to be converted into AC by
an inverter placed at the receiving
end.
Then this AC is stepped down to safe
utility voltage using transformers.

17. Milestones in HVDC
• The first modern commercial application of HVDC
transmission occurred in 1954 when the Swedish
mainland and the island of Gotland were
interconnected by a 96 km submarine cable.
• With the advent of thyristor valve converters, HVDC
transmission became even more attractive. The first
application of an HVDC system using thyristor valves
was at Eel River in 1972 – a back-to-back scheme
providing an asynchronous tie between the power
systems of Quebec and New Brunswick.

18. • With the cost and size of conversion equipment
decreasing and its reliability increasing, there has
been a steady increase in the use of HVDC
transmission.
• Interconnection of neighbouring utilities usually
leads to improved system security and economy of
operation. Improved security results from the mutual
emergency assistance that the utilities can provide.
Improved economy results from the need for less
generating reserve capacity on each system.

19. • In addition, the interconnection permits the utilities
to make economy transfers and thus take advantage
of the most economical sources of power.
• These benefits have been recognized from the
beginning and interconnections continue to grow.
• Almost all the utilities in the United States and
Canada are now part of one interconnected system.
The result is a very large system of enormous
complexity.
• The design of such a system and its secure operation
are indeed challenging problems.

20. HISTORICAL BACKGROUND
☺1880- DC at low voltage levels (Thomas Alva Edison )
☺AC system- Higher voltage levels (Nikola Tesla)
☺“war of currents”
☺1882-1930- Thury systems
☺1901-Hewitt’s mercury-vapour rectifier (HVDC Born)
☺1929- Uno Lamm’s mercury arc valves (Father of HVDC)
☺1945 – Commercial HVDC system in Berlin
☺1954 –First commercial HVDC( 96 km sea cable, 20 MW,
Sweden mainland and the island of Gotland)
☺1960- Thyristor based valve technology
☺1967 –First tested in the Gotland transmission
☺1972 –Introduced on a larger scale in Canada(320 MW)

21. HISTORICAL BACKGROUND(CONT..)
☺ First microcomputer based control equipment for
HVDC in 1979
☺ Highest DC transmission voltage (+ 600kV, 3150MW)
in Itaipu, Brazil, 1984
☺ First DC Active filter in1994
☺ HVDC 2000 developed by M/S. ABB-1995
☺ First CCC in Argentina – Brazil inter connection in
1998
☺ First VSC for transmission in Gotland Sweden in
1999
☺ +800kV,6400MW UHVDC Xiangjiaba-Shanghai-2010
*REAL HISTORY

24. Advantages of HVDC
1. The HVDC link is a asynchronous connection between two AC stations i.e.,
the transmission of power is independent of sending or receiving end
frequencies. Hence, it allows power transmission between AC networks
with different frequencies or networks, which cannot be synchronized, for
other reasons.
2. Inductive and capacitive parameters do not limit the transmission capacity
or the maximum length of a DC overhead line or cable.
3. For a long cable connection, e.g. beyond 40 km, HVDC will in most cases
offer the only technical solution because of the high charging current of an
AC cable. This is of particular interest for transmission across open sea or
into large cities where a DC cable may provide the only possible solution.
4. It provides accurate, efficient and fast control of the active power flow.
5. A lesser number of conductors and insulators are required thereby
reducing the cost and losses of the overall system.

25. 6. It requires less phase to phase and ground to ground clearance. So
their towers are less costly and cheaper.
7. An HVDC system does not contribute to the short circuit current of
the interconnected AC system. Lesser corona loss is less as
compared to HVAC transmission lines of similar power.
8. The bipolar HVDC system uses earth return. If any fault occurs in
one pole, the other pole with ‘earth returns’ behaves like an
independent circuit. This results in a more flexible system.
9. It does not generate or absorb any reactive power. So, there is no
need for reactive power compensation.
10. The conductor cross section is fully utilized because there is no
skin effect and proximity effect.
11. Fast modulation of DC transmission power can be used to damp
power oscillations in an AC grid and thus improve the system
stability .

26. * RUN UP FUNCTION

27. Economics of Long Distance HVDC
• Assume: same insulator characteristics for AC and DC and
based on peak voltage, and AC line operating at the same
current level (!)
2 * V * I <> √3 * V * I * cos f
For a given power: DC requires less ROW, cheaper towers,
less conductor, insulator costs.
but Terminal Equipment is costly
• Operational Costs : losses : AC > DC

28. DC terminal equipment are very
costly compare to AC stations.
The DC line cost and loss cost
curve is not as steep as the AC
curve because of considerably
lower line costs per kilometer.
For long AC lines the cost of
intermediate reactive power
compensation has to be taken into
account.
The break-even distance is in the
range of 500 to 800 km depending
on a number of technical and
commercial factors.

29. 29
General Cost Structure of HVDC Terminal Station
20 %
Valves
16 %
Xmers
5 % F&I
10 %
Engg.
8 %
E.T.C.
10 %
Other
Eqpt. 7 %
Control
system
10 % AC
Filter
14 %
Civil

30.  Bulk power transmission with lower line losses as no
reactive power transfer takes place
 Connect two asynchronous system.
 Provides system stability.
 Controllability of power flow at high speed.
 Additional flexibility in grid operation
 Firewall against grid disturbances
30
ADVANTAGES OF HVDC TRANSMISSION

31. ADVANTAGES OF HVDC (CONTD..)
• No skin/proximity effect
• Distance is not limited by stability point of view
• Corona effect less significant
• Environmental benefits
• Less right of way for transmission lines
• No contribution to short circuit level of the ac bus
connected.

32. ADVANTAGES OF HVDC (CONTD..)
 Exact power flow control
 Interconnected systems maintain their autonomy
 Disturbances in one system are not propagated to
the other
 Efficient use of generating capacity
 Stability control

33. Lower losses
HVDC 2x500 kV

34. Assuptions for a comparison :
- Total distance: 800 km
- Span length: 500 m
Number of towers:
Average weight:
Total weight of steel:
765 kV AC
Transmission Line
Three Lines
1600 pcs
7500 kg
3 x 1600 x 7500 = 36.000 tons
± 600 kV DC
Transmission Line
Two Bipoles
1600 pcs
5000 kg
2 x 1600 x 5000 = 16.000 tons
DC towers versus AC towers
Less than half the amount of steel !

35. 
Right Of Way (ROW)
DC
HVDC
HVAC with FACTS
Conventional HVAC

36. 400 MW AC
2000 MW DC
Comparison of AC & DC Transmission Line Corridor

37. AC transmission line require large corridors
DC line transmitting as much power
requires fewer towers
HVDC conserves forests and saves land
Transmission line corridor with HVDC Cable
HVDC cables

38. Long Distance Transmission :
AC vs DC
• DC : Power Flow is controlled (modulation for stability
enhancement, fault current limiting in DC lines is also
possible)
• Ground return possible in DC due to relatively low ground
impedance for extended periods. Buried metallic structures
may pose problems due to corrosion.
• Transformation of voltage level for utilization of not possible
without converter station.

39. Assuptions for a comparison :
- Total distance: 800 km
- Span length: 500 m
Number of towers:
Average weight:
Total weight of steel:
765 kV AC
Transmission Line
Three Lines
1600 pcs
7500 kg
3 x 1600 x 7500 = 36.000 tons
± 600 kV DC
Transmission Line
Two Bipoles
1600 pcs
5000 kg
2 x 1600 x 5000 = 16.000 tons
DC towers versus AC towers
Less than half the amount of steel !

40. Investment Costs
Distance
AC Terminal costs
Total AC cost
DC terminal
Costs
Total DC Cost
Variables -
Cost of Land -
Cost of Materials
- Cost of Labour -
Time to Market
Permits etc.
Investment costs versus distance
Critical Distance

41. Limitations of HVDC
• High cost-Conversion equipments
• Converter Station Size- Large
• Need of ancillary components- Filters,PE,Thermal M.S.
• High cost of DC circuit breakers
• Inability to use transformers to change voltage levels
• Generation of harmonics
• Complexity of control
• Link charging problem during grid failure.
• SCR must be higher than 3.
• Converters consumes reactive power

42. Limitation of HVDC transmission:
1. Converter stations needed to connect DC link to AC power grids are very
expensive, more complex and have small overload capacity.
2. In contrast to AC systems, designing and operating multi-terminal HVDC
systems is complex.
3. Converter substations generate current and voltage harmonics, consume
reactive power. As a result, it is necessary to install expensive filter-
compensation units and reactive power compensation units.
4. Grounding HVDC transmission involves a complex and difficult
installation, as it is necessary to construct a reliable and permanent contact
to the Earth for proper operation and to eliminate the possible creation of a
dangerous “step voltage.”
5. Converters consumes reactive power

44. APPLICATIONS OF HVDC
• Long undersea cable links (> 50 km)
• Long overhead lines (> 500 km)
• Interconnection of different grids or networks
• Combinations of the above
• Increasing existing grid utilization.
• Integration of generation( conventional/non-
conventional)

45. U1 sin(a1) U2 sin(a2)
X (~ distance)
)
sin( 2
1
2
1
a
a 



X
U
U
P


 30
2
1 a
a (to maintain transient stability)
HVDC
U1 sin(a1) U2 sin(a2)
Power flow independent from system angles
DC
DC I
U
P 

N
DC I
I 

0
HVAC
Interconnection with HVDC

47. AC transmission principles
P
E 1
E 2
X
sin d
X
~ ~
E1
d
=
E2
0
Power Direction
R
Ud2
Ud1
E1
d
P
Ud1
(Ud1
-Ud2
)
R
=
E2
0
~
~
DC transmission principles
HVDC Control

49. •High voltage direct current (HVDC) power systems use High voltage D.C.
(500KV or 800KV) for transmission of bulk power over long distances.
•HVDC transmission systems is more costly, but it gives improved
efficiency, stability, reliability, and transmission capacity.
•The transmission of electricity in the form of HVDC over long distances by
means of submarine cables or overhead transmission line is preferred over
EHVAC transmission. HVDC has advantage of cost, losses and many other
factors.
•The high-capacity (800-kV, 6,000-MW) HVDC bipole line is from Bishwanath
Chariali in Assam to Agra in Uttar Pradesh through Alipurduar in West
Bengal.
•The high-voltage corridor would facilitate transfer of 24,000 MW from
future generation projects in the north-eastern region and Bhutan to the
northern states.
•This line is built by Power Grid Corporation of India at an investment of Rs
12,000 crore