1. D.N.V.K.BHARGAV
13761A0274
EEE DEPARTMENT

2. OVERVIEW
• Why HVDC lines?????
• History
• Basic Structure
• Components
• Types of HVDC Systems
• HVDC Economical Attributes
• HVDC Environmental Impacts
• HVDC World Scenario
• HVDC Indian Population
• Emerging Applications
• Limitations

4. LIMITATIONS OF AC TRANSMISSION SYSTEMS
 Inductive and capacitive elements of overhead lines and cables put
limits to the transmission capacity and the transmission distance of
AC transmission links.
 This limitation is of particular significance for cables. Depending on
the required transmission capacity, the system frequency and the
loss evaluation, the achievable transmission distance for an AC
cable will be in the range of 40 to 100 km. It will mainly be limited
by the charging current.
 Direct connection between two AC systems with different
frequencies is not possible.
 Direct connection between two AC systems with the same frequency
or a new connection within a meshed grid may be impossible
because of system instability, too high short-circuit levels or
undesirable power flow scenarios.

7. HISTORY
 In 1882, a 50-km-long 2-kV DC transmission line
was built between Miesbach and Munich in
Germany.
 In 1941, the first contract for a commercial HVDC
system was signed in Germany: 60 MW were to
be supplied to the city of Berlin via an
underground cable of 115 km length. The system
with ±200 kV and 150 A was ready for energizing
in 1945. It was never put into operation.

8. AC
Transmision
Line
Converter
Station
Inverter
Station
AC Transmission
Line
Distribution
Line
HVDC
Transmission Line
TRANSMISSION SCENARIO

9. HVDC SYSTEM : STRUCTURE

10. COMPONENTS
• Thyristor Valves
• Converter Transformer
• Smoothing Reactor
• Harmonic Filter
• Surge Arrestor
• DC Transmission Circuit
• Control &Protection

11. THYRISTOR VALVES SETUP

12. THYRISTOR VALVES
 The thyristor valves make
the conversion from AC
into DC and thus are the
central component of any
HVDC converter station.
 Monitoring of the
thyristor performance is
achieved by a simple
voltage divider circuit
made from standard off-
the-shelf resistors and
capacitors .

13. SIX PULSE RECTIFIER

14. TWELVE PULSE RECTIFIER

15. CONVERTER TRANSFORMER
• The converter transformers transform the voltage of the
AC busbar to the required entry voltage of the
converter.
• At the same time, they ensure the voltage insulation
necessary in order to make it possible to connect
converter bridges in series on the DC side, as is
necessary for HVDC technology.

17. CONVERTER TRANSFORMER
ATTRIBUTES
 Main components of the
Converter Transformer
are:
• Core
• Tank
• Windings
• Bushings
 HVDC transformers are
subject to operating
conditions that set them
apart from conventional
system or power
transformers. These
conditions include:
• Combined voltage
stresses
• High harmonics content
of the operating current
• DC pre magnetization of
the core

18. SMOOTHING REACTOR
 Functions of Smoothing
Reactor:
• Prevention of
intermittent current
• Limitation of the DC fault
currents
• Prevention of resonance
in the DC circuit
• Reducing harmonic
currents

19. SMOOTHING REACTOR ATTRIBUTES
 There are basically two
types of reactor design:
• Air-insulated dry-type
reactors
• Oil-insulated reactors in
a tank
 The reactor type should
be selected taking the
following aspects into
consideration:
• Inductance
• Costs
• Maintenance and
location of spare units
• Seismic requirements

20. HARMONIC FILTERS
 The filter arrangements of an HVDC converter
station have two main duties:
• to absorb harmonic currents generated by
the HVDC converter and thus to reduce the
impact of the harmonics on the connected AC
systems, like AC voltage distortion and
telephone interference
• to supply reactive power for compensating the
demand of the converter station

22. DESIGN CRITERIA
 Reactive Power Requirements
 Harmonic Performance Requirements
• (the characteristic harmonics are of the order
n = (12 * k) ± 1 (k = 1,2,3 ...). )
 Network Impedance

23. SURGE ARRESTERS
Surge arresters are
designed optimally to the
following requirements:
• Excellent pollution
performance for coastal
and desert regions or in
areas with extreme
industrial air pollution.
• High mechanical stability,
e.g. for use in seismic
zones.
• Extremely reliable
pressure relief behavior
for use in areas requiring
special protection.

24. SURGE ARRESTERS CRITERIA
 The main task of an arrester is to protect the
equipment from the effects of over voltages.
 During normal operation, it should have no negative
effect on the power system.
 Moreover, the arrester must be able to withstand
typical surges without incurring any damage.
 Non-linear resistors with the following properties fulfill
these requirements:
• Low resistance during surges so that over voltages are
limited
• High resistance during normal operation in order to
avoid negative effects on the power system and
• Sufficient energy absorption capability for stable
operation

25. DC TRANSMISSION CIRCUIT
 DC transmission lines are mechanically
designed as it is practice for normal AC
transmission lines; the main differences are:
• The conductor configuration
• The electric field requirements
• The insulation design

26. INSULATION ASPECTS
 There are 3 different types of insulators
applicable for DC transmission lines:
• Cap and pin type
• Long-rod porcelain type
• Composite long-rod type

27. Cap and Pin Porcelain Long-Rod Composite Long-Rod
Insulator string
length
5270 mm
31 insulators
5418 mm
4 insulators
4450 mm
1 insulator
Creepage per unit 570 mm 4402 mm 17640 mm
Weight of string 332 kg 200 kg 28 kg
Breaking load 160 kN 160 kN 160 kN

28. DC CONDUCTORS

29. DC CABLE
 For HVDC submarine cables there are different
types available:
1. Mass-Impregnated Cable
2. Oil-Filled Cable
3. XLPE(Cross-Linked Poly Ethene)
4. Lapped Thin Film Insulation

30. ■2 Insulation material
■3 Core screen
■4 Lead alloy sheath
■5 Polyethylene jacket
■6 Reinforcement of steel tapes
■7 Bedding
■8 Armour of steel flat wires
■1 Conductor of copper-shaped wires

31. CONTROL & PROTECTION
 Main objectives for the implementation of the
HVDC control system are reliable energy
transmission which operates highly efficient and
flexible energy flow that responds to sudden
changes in demand thus contributing to network
stability.
 The control is divided into the following
hierarchical levels:
• Operator control level (WIN CC)
• Control and protection level (Simatic TDC)
• Field level (I/Os, time tagging, interlocking)

32. HVDC CONFIGURATIONS

33. HVDC ATTRIBUTES

34. ENVIRONMENTAL ISSUES
• An HVDC transmission system can produce effects on
environment through several potential impacts
occurring during both its construction and working
phase
• Some main recurring impacts during the construction
phase are related to cable landing, that could generate
interferences to marine flora and fauna, due for
example to sediment suspension, use of sonar, noise
emission and possible collision with operation vessels.
• During the working phase the generation of electric
and magnetic fields are predictable; this can annoy the
marine fauna and navigation system based on
magnetic compasses.

35. Usually, the main environmental components that could
be interfered by an HVDC project are:
• Water (sea bottoms, water streams, quality water)
• Biosphere (marine and land flora, fauna and habitat)
• Population (interferences with fishing and navigation,
traffic)
• Landscape (landscape degradation)
• Soil (occupation and consume of valuable soils)
• Electric and Magnetic fields
• Micro clime (heat generation)
• Noise (annoyance to marine fauna and population)

38. HVDC SCENARIO IN INDIA
HVDC LINK CONNECTING
REGION
CAPACITY
(MW)
Vindyachal North – West 2 x 250
Chandrapur West – South 2 x 500
Vizag – I East – South 500
Sasaram East – North 500
Vizag – II East – South 500

40. EMERGING APPLICATIONS
HVDC can be effectively used in a number of key
areas as follows
• Power supply to island.
• Remote small-scale generation
• Off-shore generation and deep sea crossing
• Multi-terminal systems.
• From the technology point of view, wind farm and
off-shore wind farms in particular are well-suited
for VSC-HVDC application.

41. ADVANTAGES OF DC TRANSMISSION SYSTEMS
 There are two conductors used in DC transmission
while three conductors required in AC transmission.
 There are no Inductance in DC transmission.
 Due to absence of inductance, there are very low
voltage drop in DC transmission lines comparing with
AC (if both Load and sending end voltage is same)
 There is no concept of Skin effect in DC transmission.
Therefore, small cross sectional area conductor
required.
 A DC System has a less potential stress over AC system
for same Voltage level. Therefore, a DC line requires
less insulation.
 In DC Line, Corona losses are very low.

42. CONTINUED…………….
 In High Voltage DC Transmission lines, there are no Dielectric losses.
 In DC Transmission system, there are no difficulties in synchronizing and
stability problems.
 DC system is more efficient than AC, therefore, the rate of price of Towers,
Poles, Insulators, and conductor are low so the system is economical.
 In DC System, the speed control range is greater than AC System.
 There is low insulation required in DC system (about 70%).
 The price of DC cables is low (Due to Low insulation)
 In DC Supply System, the Sheath losses in underground cables are low.
 DC system is suitable for High Power Transmission based on High Current
transmission.
 In DC System, The Value of charging current is quite low, therefore, the
length DC Transmission lines is greater than AC lines.

43. LIMITATIONS OF HVDC SYSTEMS
• Due to commutation problem, Electric power can’t be
produce at High (DC) Voltage.
• For High Voltage transmission, we can not step the level of
DC Voltage (As Transformer can not work on DC)
• There is a limit of DC Switches and Circuit breakers (and
costly too)
• Motor generator set is used for step down the level of DC
voltage and the efficiency of Motor-generator set is low
than transformer.
• So the system makes complex and costly.
• The level of DC Voltage can not be change easily. So we can
not get desire voltage for Electrical and electronics
appliances (such as 5 Volts, 9 Volts 15 Volts, 20 and 22 Volts
etc) directly from Transmission system.

44. SUMMARY
HVDC systems remain the best
economical and environmentally friendly option
for the above conventional applications.
However, three different dynamics - technology
development, deregulation of electricity industry
around the world, and a quantum leap in efforts
to conserve the environment - are demanding a
change in thinking that could make HVDC systems
the preferred alternative to high voltage AC
systems in many other situations as well.

45. REFERENCES
• Understanding Facts: Concepts and Technology of
Flexible AC Transmission Systems, Narain G.
Hingorani, Laszlo Gyugyi
• Flexible AC transmission systems, Song & Johns
• www.google.com
• Siemens HVDC references
http://www.energy.siemens.com/hq/en/power-
transmission/hvdc/hvdc-ultra/references.htm
Alstom HVDC resources
http://www.alstom.com/