1. 1. Welcome
2. 2. HVDC Transmission Seminar On Submitted To:- Prof. Anshul Bhati Prof. Vikram Singh Rajpurohit Submitted By:- Nadeem Khilji 11EVEEX032 8th Sem. EX
3. 3. Evolution HVDC Technology
4. 4. Agenda HVDC-Introduction Challenges with AC Power Lines Solution HVDC Technology Advantages Working Components HVDC Configurations Ground Return Earth Electrode HVDC Plus
5. 5. HVDC- Introduction 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. HVDC also allows transfer of power between grid systems running at different frequencies, such as 50 Hz and 60 Hz. Compared to alternating current, the direct current system is less expensive and loses less energy.
6. 6. Challenges with AC Power Lines Reduced Power quality causes the risk of declining network stability. Corona Loss & Radio Interference. High Short Circuit Currents Line Support More Insulation Requirement Erection Difficulties
7. 7. Solution: HVDC Technology It provides improved Power quality and Power flow control as well. More Power can be Transmitted per Conductor Introducing extruded DC-cables which have no technical limit to distance which can be installed. It can provide an alternative to overhead lines particularly when the total capital and environmental costs are considered.
8. 8. Advantages Advantages of HVDC Technical Advantages Economic Advantages
9. 9. Technical Advantages Smaller Tower Size Use of Ground Return Possible No Skin Effect Stable System Less Corona & Radio Interference Asynchronous Interconnection Possible Lower Short Circuit fault levels Power can be easily controlled
10. 10. 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.
11. 11. Lower Investment Cost It is true that HVDC terminal stations are more expensive due to the fact that they must perform the conversion from AC to DC, and DC to AC. But over a certain distance, the so called "break-even distance" (approx. 600800 km), the HVDC alternative will always provide the lowest cost
12. 12. Cost Structure Source: High Voltage Direct Current (HVDC)Transmission Systems Technology Review Paper Presented at : Energy Week 2000, Washington, D.C, USA, March 7-8, 2000
13. 13. How does it work ? HVDC transmission utilizes a converter station at either end of the system. A mercury arc valve or solid state valve (Thyristor) is used for the conversion of AC and DC current. The valve at the beginning of the system converts alternating current to HVDC, the HVDC travels to the next location through a cable. The valve at the end of the system converts the HVDC back to alternating current.
14. 14. Wind Power AC Transmission Line AC to DC Converter Station HVDC Transmission Line DC to AC Converter Station AC Transmission Line Distribution Line HVDC transmission system
15. 15. Components of an HVDC Transmission system Source: High Voltage Direct Current (HVDC)Transmission Systems Technology Review Paper Presented at : Energy Week 2000, Washington, D.C, USA, March 7-8, 2000
16. 16. Transmission Medium For Bulk Power Transmission over land, the most frequent transmission medium used is the overhead line. This overhead line is normally Bipolar, i.e. two conductors with different polarity. HVDC cables are normally used for Submarine Transmission. The most common types of cables are the solid and the oil filled ones. HVDC underground or submarine power transmissions: This new HVDC cable is made of Extruded Polyethylene, and is used in VSC based HVDC systems.
17. 17. HVDC configurations
18. 18. Monopolar Link One of the terminal of the converter is connected to the transmission line, while the other terminal is connected to the ground. The ground is used as a return path here. Also Monopolar link can be used to transmit power over sea by using special electrode for the earth return.
19. 19. Bipolar Link There are two pole/conductors. One operates at positive polarity and other is on negative polarity. The Bipolar link seems to be costlier than Monopolar, but it is more reliable than Monopolar. The advantage of Bipolar is that whenever one of the poles fails; the system operates as Monopolar link with the ground as return path.
20. 20. Multi terminal Link A Multi terminal HVDC system is used to connect with more than two converter stations. complex network as compared to Monopole and Bipolar HVDC link. The reversal of power can be easily achieved using the Multi terminal HVDC link.
21. 21. Back to Back (B2B) Used to connect the asynchronous system with different frequencies. The length of the back to back connection is kept very small. Sometimes it may vary depending on the system requirement. Helps to achieve the connection between any asynchronous systems.
22. 22. Converter Station Equipment Thyristor valves Converter Transformer DC Reactor Harmonics Filtering Equipment Control Equipment Reactive power compensation
23. 23. Converters 6 Pulse Rectifier
24. 24. 6 Pulse Rectifier Waveform
25. 25. 6 Pulse Rectifier Working
26. 26. 6 Pulse Inverter Operation
27. 27. 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.
28. 28. 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.
29. 29. HVDC Links HVDC Links are installed world wide some of the examples are as follows: In World S.No. Name Location Total Length (Km) Volt (KV) Power (MW) Type 1 Rio Madeira Rio Madeira Transmission Link, Brazil 2385 600 7100 Thyristor 2 Jinping-Sunan Jinping-Sunan Transmission Link, China 2090 800 (UHVDC) 7200 Thyristor 3. Inga-Kolwezi Inga-Kolwezi Transmission Link, Congo 1700 500 560 Thyristor 4. Talcher-Kolar Talcher-Kolar Transmission Link, India 1450 500 2500 Thyristor 5. Nor Ned Feda (Norway)- Eemshaven(Netherl ands) Submarine Power Cable 580(Submarine) 450 700 Thyristor
30. 30. HVDC Links in India :- S.No . Name Total Length (Km) Volt (KV) Power (MW) Mode of Operation Type 1 Bishwanath-Agra Transmission Link, India 1728 (Com.) 800 6000 Multi Terminal Thyristor 2 Rihand-Dadri Transmission Link, India 816 500 1500 Bipolar Thyristor 3. Ballia-Bhiwadi Transmission Link, India 780 500 2500 Bipolar Thyristor 4. Mundra-Mohindergarh Transmission Link, India 986 500 1500 Bipolar Thyristor
31. 31. Disadvantages The disadvantages of HVDC are in conversion, switching, control, availability and maintenance. HVDC is less reliable and has lower availability than alternating current (AC) systems, mainly due to the extra conversion equipment. The required converter stations are expensive and have limited overload capacity. At smaller transmission distances, the losses in the converter stations may be bigger than in an AC transmission line for the same distance. Operating a HVDC scheme requires many spare parts to be kept, often exclusively for one system, as HVDC systems are less standardized than AC systems and technology changes faster.
32. 32. HVDC Plus Technology Also known as IGBT Technology Its Self Commutated Technology No Harmonic Filters Conventional AC Transformers Compact Footprint Independent Active/Reactive Power Control Output Waveform is Very Close to Sine wave due to Multi Level Switching
33. 33. HVDC Plus Technology
34. 34. Conclusion HVDC offers Powerful Alternative to increase stability of a power system as well as to improve system operating flexibility and loss reduction. Removes the Synchronization Problem.