PREPARED BY
SUNIT KUMAR SAHOO

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Why we need HVDC ?
ADVANTAGES
Technical Advantages
 Reactive power requirement
 System stability
 Short Circuit Current
 Independent Control of ac system
 Fast change of energy flow
 Lesser Corona Loss and Radio interference
 Greater Reliability.
 Economic advantages
 Comparison between the prices of AC & DC Transmission
 Monopolar link
 Bipolar Link
 Incorporating HVDC into AC systems
 Two terminal DC page link point to point transmission.
 Back to Back DC link
 DC line in Parallel with AC link.
 Multi-Terminal DC link.
CONVERTER STATION EQUIPMENT
 Thyristor valves
 Converter Transformer
 DC Reactor
 Harmonics Filtering Equipment
 Control Equipment
 Reactive power compensation
GROUND RETURN
• Most dc transmission lines use ground return for reasons of economy and reliability
 Ground return are used by the monopolar and the bipolar page link for carrying the return current.
 The ground path has a low resistance and, therefore low power loss as compared to a metallic conductor path provided the ground electrodes are properly designed.
 The resistance of the ground path is independent of the depth of the line.
 Typical tower structure and rights of way for alternative transmission system of 2000 MW capacity
PROBLEMS
 The Design of grounding electrodes for low cost of installation and maintenance
 Location and screening of electrodes so that ground currents cause negligible electrolytic corrosion of buried and immersed metallic structures.
EARTH ELECTRODE
 HVDC system requires a properly designed earth electrode at each station.
 The electrode is situated at a safe distance (5 to 30 km) from the station.
 The earth electrode at one of the station acts as a anode and at the other end acts as a cathode.
RECENT ADVANCES
 GTO’s have come into use.
 Use of active ac and dc filters.
 Advanced fully digital control systems using optical fibers.
CONCLUSION
 Recent studies indicate that HVDC systems are very reliable.
 The data collected from 31 utilities says that forced unavailability of energy due to the converter station is 1.62%
 The scheduled unavailability of energy is about 5.39%.