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1. HVDC TRANSMISSION SYSTEM

2. CONTENTS:
• HISTORY.
• INTRODUCTION.
• WHY PREFERS.
• HOW DOES IT WORKS.
• ADVANTAGES/DISADVANTAGES
• HVDC FOR RENEWABLE SOURCES.
• CONCLUSION

3. History.
• Firstly HVDC b/w Swedish and Gotland in 1954.
• In North America, total HVDC transmission
capacity in 1987 was 14,000 MW.

4. INTRODUCTION
• HVDC stands for.
• for long distance transmission.
• requires converter stations at each end of the
line.
• can interconnect diff power systems( i.e 50 Hz
and 60 Hz)

5. HVAC
ADVANTAGES
• Voltage transformation.
• Easy conversion into mechanical.
energy and vice versa.
LIMITATIONS
• Long distance transmission
• Difficult to use cables, already at 100
km high reactive power consumption

6. NEEDS OF HVDC
The losses which occurs in the systems are at all the
stages
i.e. , at generation , transmission & distribution
level.
The losses at transmission level can be greatly
reduced by HVDC transmission.

7. WHY TO PREFER HVDC THAN HVAC?
 Long distance transmission
 5 times more energy transmits than AC(same lines)
 Less losses (no inductance, capacitance).
 Cost of transmission medium & land is low.
 Maintenance & operation cost is low.
 Initial cost is high but overall cost is low than ac.

9. COMPARISON B/W AC & DC
TRANSMISSION COST.

10. HVDC TECHNOLOGY
• If DC is required to be used for transmission
and since our primary source of power is A.C,
• The following are three basic steps:-
1. Convert AC into DC (rectifier)
2. Transmit DC
3. Convert DC into AC ( inverter)

11. HOW IT WORKS ?

12. COMPONENTS OF HVDC
TRANSMISSION SYSTEMS
• Converters
• Smoothing reactors
• Harmonic filters
• Reactive power supplies
• Electrodes
• DC lines
• AC circuit breakers

13. CONVERTERS
• Perform AC/DC (rectifier) and DC/AC (inverter) conversion
• consist of bridges and transformers
DC SMOOTHING REACTORS
• Decrease harmonics in voltages and currents in DC lines.
• Prevent current from being discontinuous.
AC HARMONIC FILTERS
• Used to reduce harmonics (in voltages and currents) caused by
converters which generate harmonics,
• Hence prevent from interference with any comm system.

14. REACTIVE POWER SUPPLIES
• Converter may consume reactive pwr of abt 50% / more of active pwr.
• Reactive power is, therefore, provided near converter.
• For a strong AC power system, this reactive power is provided by a shunt
capacitor.
ELECTRODES
• Used to provide connection to the earth for neutral.
DC LINES
• They may be overhead lines or cables.
• DC lines are very similar to AC lines.
CIRCUIT BREAKERS
• Used to break cct if fault occurs in the transformer and for taking the DC
link out of service.

16. 6 PULSE RECTIFIER

17. 6 PULSE RECTIFIER WAVEFORM

19. 6 PULSE RECTIFIER

20. INVERTER OPERATION.

21. CONTROL OF HVDC SYSTEMS
Objectives of Control
• Efficient and stable operation.
• Maximum flexibility of power control without
compromising the safety of equipment.
• Implementation and their performance during normal
and abnormal system conditions.

22. BASIC MEANS OF CONTROL
• This can be accomplished by:
• Controlling firing angles of the rectifier and inverter.
• Controlling alpha is done by amount of gate current.
• Lesser the angle, more stable the signal.

23. BASIC PRINCIPLES OF CONTROL
• Direct current from the rectifier to the inverter
• Power at the rectifier terminal
• Power at the inverter terminal
cilcr
doidor
d
RRR
VV
I



 coscos
ddrdr IVP 
2
dLdrddidi IRPIVP  Schematic diagram of control

24. POWER FLOW DIRECTION
• Decrease voltage at station B or increase voltage at station A,
power flows from A to B.

26. • Power reversal is obtained by reversal of polarity of both
direction.

27. APPLICATION BASED HVDC TRANSMISSION TYPES
• Unique solution to connect asynchronous systems or grids
with different frequencies.

28. • Most economical solution to transmit electrical energy over
distance more than 600km.

29. • Alternative to submarine transmission, also economical for
shorter distances i.e 10 km or more.

30. FOR 10 KM

31. Types of DC links
Monopolar
Bipolar
Homopolar

32. MONOPOLAR LINKS
• It uses one conductor .
• Return path by ground/water.
• Due to –ive polarity, no corona effect occurs.

33. BIPOLAR LINKS
• Has two conductors.
• Junction b/w the conductors is grounded.
• Can carry half the rated load, if fault occurs in
one pole.

34. HOMOPOLAR LINKS
• Has two conductors polarity( usually
negative.)
• The return path for such a system is through
ground.

35. ADVANTAGES

36. TECHNICAL ADVANTAGES
• System stability
• less Corona Loss and no skin effect
• Greater Reliability.

37. ECONOMIC ADVANTAGES
• Trans Lines => less lines & less meterial required,
cheaper.
• Towers => narrower, simpler and cheaper
• Line losses => less increases efficiency.
• Earlier lines can be used.

38. DISADVANTAGES
• Power loss in conversion, switching and
control.
• Expensive inverters.
• Per kilometer cost reduces if lines are of fairly
of large distances.

39. HVDC FOR RENEWABLE ENERGY
SOURCES.

40. EXAMPLES OF PROJECTS
1) Gotland – HVDC
• Capacity: 50 MW
• Length: 70 km
• In operation since 1999
Requirements
• additional wind power, 90 MW
• minimized environmental
impact

41. GOTLAND PROJECT

42. HVDC PLUS
• Known as IGBT TECHNOLOGY
• IGBT can be turned on and off in controlled
manner.
• Switching up to 200 levels making it efficient,
giving more smooth ac signal.

43. HVDC PLUS TECHNOLOGY.

44. HVDC IN PAK
• 1000 MW from Taftan to Quetta through a
500 KV,HVDC transmission line, under
discussion (from IRAN).
• Proposed 500 MW from India through a
400 KV AC transmission line and a back-to-
back HVDC converter in Pakistan, estimated
construction time 24-30 months

45. CONCLUSION
• Recent studies indicate that HVDC systems are very
reliable.
• Very large investments in e.g in China and India
shows that high-voltage direct current will very
important in the future, especially in big, new-
industries countries.

46. •Thank you!