Role of Power electronics in HVDC and Transmission system. What are the components of Power electronics used in HVDC. Types of HVDC Links. Advantages of HVDC over HVAC.

1. APPLICATIONS OF POWER
ELECTRONICS - HVDC
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2. CONTENTS
 Introduction
 HVDC
 Need for HVDC
 Components of HVDC
 Types of HVDC Links
 Advantages
 Disadvantages
 Conclusion
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3. INTRODUCTION
 Power Electronics is the study of switching electronic circuits
in order to control the flow of electrical energy.
 It is literally impossible to list all the applications of power
electronics today, as it has penetrated almost all the fields.
 Some of the few are listed below,
 Aerospace and Defense
 Automotives and Traction
 Home Appliances
 Telecommunication
 Utility System and Renewable energy
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4. HVDC
 A High Voltage Direct Current (HVDC) electric power transmission
system uses direct current for the bulk transmission of electrical
power, in contrast with the more common alternating current (AC)
systems.
 HVDC allows power transmission between unsynchronized AC
transmission systems.
 For long distance transmission, HVDC systems may be less
expensive and suffer lower electrical losses.
 An HVDC link can be controlled independently of the phase angle
between source and load.
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5. NEED FOR HVDC
 As the load demand increases, for higher efficiency there must
be only two possibilities,
 To increase the generation
 Minimize the losses
 The losses which occur at all the stages in the system at
generation, transmission and distribution level.
 As the losses are greater in AC than DC, the losses can be
greatly reduced by HVDC transmission.
 Although there are certain in advantages of HVDC systems but
also have the limitations.
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6. COMPONENTS OF HVDC
 Converters
 Smoothing reactors
 Harmonic filters
 Reactive power supplies
 Electrodes
 DC Lines
 AC Circuit breakers
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7. COMPONENTS (Contd.,)
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 CONVERTERS:
Perform AC to DC and DC to AC conversion.
HVDC converters are usually built as 12-pulse circuits.
Consists of valve bridges and transformer.
 SMOOTHING REACTORS:
Smoothing Reactors are serially connected reactors inserted in DC
systems to reduce harmonic currents and transient over currents and/or
current ripples in DC systems.
Prevent commutation failure in inverter.

8. COMPONENTS (Contd.,)
 HARMONIC FILTERS:
 Harmonic filters is used to eliminate these harmonics.
 Converters generates harmonics in voltages and current.
These Harmonics cause the over heating of capacitors and
nearby generators and interference with Telecommunication
systems.
 DC LINES:
They may be overhead lines or cables. DC lines are very similar
to AC lines.
 AC CIRCUIT BREAKER:
They used to clear the faults in transformer and for taking DC
link out of service.
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9. COMPONENTS (Contd.,)
 REACTIVE POWER SUPPLIER:
Under steady state condition, the reactive power
consumed by the converter is about 50% of the active power
transferred. Under transient conditions it could be much higher.
For a strong AC power system, this reactive power is provided by
a shunt capacitor.
 ELECTRODES :
Electrodes are conductors that provide connection to
the earth for neutral and they have large surface to minimize
current and surface voltage gradients.
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10. TYPES OF HVDC
LINKS
 Monopolar links
 Bipolar links
 Homopolar link
 Back to Back Links
 Multi terminal links
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11. MONOPOLAR LINKS
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 It has a single
conductor of
negative polarity.
 It uses earth or sea
for the return path
of current.
Sometimes the
metallic return is
also used.
 Two converters are placed at the end of each pole.
 But this link has several disadvantages because it uses earth as a return
path.
 The monopolar link is not much in use nowadays.

12. BIPOLAR HVDC LINK
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 The Bipolar link has
two conductors one is
positive, and the other
is negative to the
earth.
 The midpoints of the
converter stations are
earthed through
electrodes.
 Advantage:
If any of their links stop operating, the link is converted into
Monopolar mode because of the ground return system.
The half of the system continues supplies the power.

13. HOMOPOLAR HVDC
LINK
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 It has two or more
conductors all
having the same
polarity, usually
negative
 Since the corona
effect in DC
transmission lines
is less for
negative polarity.
 The return path for such a system is through ground.
 The homopolar system is not used presently.

14. BACK TO BACK LINE
HVDC LINK
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 Usually
bipolar
without earth
return.
 Converter &
inverters are
located at the
same place.
 No HVDC Transmission line.
 Provides Asynchronous tie between two different AC
networks.
 Power transfer can be in either direction.

15. MULTIPLE TERMINAL
HVDC LINK
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 There are two possible connection for MT HVDC Schemes:
Constant voltage parallel scheme
Constant current series scheme
Three or more
terminals
connected in
parallel, some
feed power and
some receive
power from HVDC
Bus.

16. ADVANTAGES
 Loss is very less as no frequency reversals taken into account
 Interconnection of asynchronously operated power
Systems
 Absence of transmission line limitations
 Simple in construction
 Fast change of energy flow i.e. Ability of quick and
bidirectional control of energy flow
 Lesser corona loss and radio interference
 Greater reliability
 Can be used for submarine and underground transmission
 Low cost of DC lines, cables and Insulators and towers.
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17. DISADVANTAGES
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 Use of converters ,filters etc increases the overall cost
 Expensive inverters with limited overloading capacity
 DC circuit breakers are more expensive
 HVDC converters have low overloading capacity
 More maintenance is required for insulators
 Voltage transformation is possible only on AC side
 Higher losses in the static inverter at smaller transmission

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