“HVDC TRANSMISSION” SUNIT KUMAR SAHOO REG NO-S BRANCH-EEE PREPARED BY

What is HVDC?.The HVDC technology is used to transmit electricity over long distances by overhead transmission lines or submarine cables..It is also used to interconnect separate power systems, where traditional alternating current (AC) connections can not be used. INTRODUCTION.The first dc link was set up in 1954 in between Swedish main land and the island of Gotland.

Now a days large blocks of power are needed to be transmitted. There arises some technical problems of transmitting power to such a long distance using ac. In the view of the draw backs of ac the HVDC transmission has come into picture. Why we need HVDC ?

ADVANTAGES Advantages of dc transmission Technical Advantages Economic Advantages

Technical Advantages Technical Advantages Reactive power requirement Reactive power requirement System stability System stability Short Circuit Current Short Circuit Current Independent Control of ac system Independent Control of ac system Fast change of energy flow Fast change of energy flow Lesser Corona Loss and Radio interference Lesser Corona Loss and Radio interference Greater Reliability. Greater Reliability.

No limits in transmitted distance Direction of power flow can be changed very quickly

Economic advantages DC lines and cables are cheaper than ac lines or cables. The towers of the dc lines are narrower, simpler and cheaper compared to the towers of the ac lines. Line losses in a dc line are lower than the losses in an ac lines.

Comparison between the prices of AC & DC Transmission

Types of DC links Monopolar Bipolar Homopolar

Monopolar link

Bipolar Link

Incorporating HVDC into AC systems Two terminal DC link point to point transmission. Two terminal DC link point to point transmission. Back to Back DC link Back to Back DC link DC line in Parallel with AC link. DC line in Parallel with AC link. Multi-Terminal DC link. Multi-Terminal DC link.

CONVERTER STATION EQUIPMENT Thyristor valves Thyristor valves Converter Transformer Converter Transformer DC Reactor DC Reactor Harmonics Filtering Equipment Harmonics Filtering Equipment Control Equipment Control Equipment Reactive power compensation Reactive power compensation

Converter transformers of one pole at Talcher, in front of the valve hall. AC harmonic filter area at Talcher

GROUND RETURN Most dc transmission lines use ground return for reasons of economy and reliability Most dc transmission lines use ground return for reasons of economy and reliability Ground return are used by the monopolar and the bipolar link for carrying the return current. Ground return are used by the monopolar and the bipolar 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 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. 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 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. 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. 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 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. 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. GTO’s have come into use. Use of active ac and dc filters. Use of active ac and dc filters. Advanced fully digital control systems using optical fibers. Advanced fully digital control systems using optical fibers.

CONCLUSION Recent studies indicate that HVDC systems are very reliable. 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 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%. The scheduled unavailability of energy is about 5.39%.

Thank you!