PowerPoint Presentation: 1 12/12/2011 “HVDC TRANSMISSION” UCE BURLA HEMANT KUMAR NAYAK ELECTRICAL ENGGINERING REG. NO.-0401101184 PowerPoint Presentation: 2 12/12/2011 INTRODUCTION 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. PowerPoint Presentation: 3 12/12/2011 The first dc link was set up in 1954 in between Swedish main land and the island of Gotland. The use of an HVDC link in an ac system requires converter stations at each end of the line. HISTORY: 4 12/12/2011 HISTORY IN the initial stages dc used to be employed for generation ,transmission and distribution of electric power. The first 110V D C central electric station was installed by Edison in New York in1882.with the introduction of transformer and 3-phase ac system the situation changed in favors of ac .for many reasons ,such as facility of transformations of voltages from one level to another ,better performance of ac motors and superiority of ac generators in comparison to dc generator ,the power was generated ,transmitted, distributed and utilized in the form of ac. But the supporters of DC carried out extensive research on dc field And found the advantages of dc in high and extra high voltage of transmission for long distance . PowerPoint Presentation: 5 12/12/2011 with the successful development of high power thyristers the HVDC transmission become technically and commercially viable alternative to EHV/UHV-AC transmission. The first dc link was setup in 1954 between Swedish mainland and island of got land .This was a Monopolar ,100KV,20MW,cable system making use of sea return .the England –France cross Channel dc link was commissions in1961.this was bipolar +-100KV,160MW,Cable system over a distance of 65 KM .since then more and more HVDC system have been set up in the world. PowerPoint Presentation: 6 12/12/2011 HVDC Transmission has also been introduced in India .A +-500kv ,1500mw,810km bipolar HVDC line has already been set up between Rihand and Delhi. it is designed to operate in bipolar ,monopolar ground return ,and Monopolar metallic return mode. Vindhyachal HVDC back to back system for exchanging power between northern and western region in either direction . PowerPoint Presentation: 7 12/12/2011 Chandarpur-padghe bipolar system (-+500kv,1500mw,736km),Jeypore back to back project(2*250mw),ana Mau back to back project (2*250mw)are also proposed . At present the world has over 50 HVDC schemes in operation for a total capacity of more than 50,000mw and the capacity is increasing by about 2000mw every year. why high voltage for transmission? : 8 12/12/2011 why high voltage for transmission? Because with increase in transmission voltage with same power supply the current in the conductor decreases. so size of the conductor decreases and since current in the conductor decrease so losses are decreases and hence efficiency of the line increases. so high voltage is used in transmitting the power .also the voltage regulation will improve. Reduction of electrical losses, increase in transmission efficiency ,improvement of voltage regulation and reduction in conductor material requirement. Line losses are reduced since line losses are inversely proportional to transmission voltage . PowerPoint Presentation: 9 12/12/2011 Transmission efficiency increases because of reduction in line losses . Voltage regulation will improve because of reduction of percentage of line drop . Size of the conductor material required is inversely proportional to the square of supply voltage . Flexibility for future system growth. Increase in transmission capacity of the line . Increase of surge impedance loading(load carrying capability of it’s supply line ). PowerPoint Presentation: 10 12/12/2011 Disadvantage of HVAC? with increase in distance and voltage the problems associated with ac systems increase. these problems are of Corona loss and radio interference. Heavy supporting structure and erection difficulties . Insulating problem . Stability problem. Current carrying capacity. Ferranti effect. Surge impedance loading. Mechanical vibrations and oscillations. Radio interference. PRINCIPLE OF OPERATION OF HVDC LINE: 11 12/12/2011 PRINCIPLE OF OPERATION OF HVDC LINE It required two ac system which are to be connected by dc link. Step-up transformer at sending end and step-down transformer at receiving end. Two Converter station one at sending end for converting ac to dc and other at receiving end for converting dc to ac. By changing the firing angle it act as rectifier(0 to 90) deg. And inverter (90 to 180)deg. .so it can operate in bidirectional flow of power. The dc out-put voltage magnitude can be controlled by changing the firing angle of the converter. In practical HVDC converter station three-phase bridge converter are employed at both end . PRINCIPLE OF OPERATION OF HVDC LINE: 12 12/12/2011 PRINCIPLE OF OPERATION OF HVDC LINE It required two ac system which are to be connected by dc link. Step-up transformer at sending end and step-down transformer at receiving end. Two Converter station one at sending end for converting ac to dc and other at receiving end for converting dc to ac. By changing the firing angle it act as rectifier(0 to 90) deg. And inverter (90 to 180)deg. .so it can operate in bidirectional flow of power. The dc out-put voltage magnitude can be controlled by changing the firing angle of the converter. In practical HVDC converter station three-phase bridge converter are employed at both end . ADVANTAGES : 13 12/12/2011 ADVANTAGES Advantages of dc transmission Technical Advantages Economic Advantages : 14 12/12/2011 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. No limits in transmitted distance Direction of power flow can be changed very quickly Economic advantages: 15 12/12/2011 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. PowerPoint Presentation: 16 12/12/2011 Comparison between the prices of AC & DC Transmission : 17 12/12/2011 Comparison between the prices of AC & DC Transmission PowerPoint Presentation: 18 12/12/2011 Types of DC links Monopolar Bipolar Homopolar Monopolar link: 19 12/12/2011 Monopolar link Bipolar Link: 20 12/12/2011 Bipolar Link Incorporating HVDC into AC systems: 21 12/12/2011 Incorporating HVDC into AC systems Two terminal DC link point to point transmission. Back to Back DC link DC line in Parallel with AC link. Multi-Terminal DC link. ESSENTIAL PARTS OF HVDC SYSTEM: 22 12/12/2011 ESSENTIAL PARTS OF HVDC SYSTEM AC sub station and HVDC sub station at each terminal. Interconnecting HVDC lines. Electrode lines and earth electrodes. MAIN PARTS OF HVDC TERMINAL SUBSTATION: 23 12/12/2011 MAIN PARTS OF HVDC TERMINAL SUBSTATION AC switchyard. Thyristor valves. Converter Transformer. DC Reactor. Harmonics Filtering Equipment. Control Equipment. Reactive power compensation. HVDC yard. Electrical and mechanical auxiliaries. GROUND RETURN: 24 12/12/2011 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 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. PROBLEMS: 25 12/12/2011 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: 26 12/12/2011 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: 27 12/12/2011 RECENT ADVANCES GTO’s have come into use. Use of active ac and dc filters. Advanced fully digital control systems using optical fibers. CONCLUSION: 28 12/12/2011 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%. PowerPoint Presentation: 29 12/12/2011 Thank you!