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High Voltage Direct Current (HVDC)
Table of Contents
Abstract ........................................................................................................................................... ii
- Introduction ............................................................................................................................. 1
- History & Evolution ................................................................................................................ 2 2.1 The Need For HVDC ............................................................................................................ 2 2.2 First Commercial Project – Gotland 1 .................................................................................. 3 2.3 Rapid Development of HVDC Technology .......................................................................... 4
- Advantages & Disadvantages .................................................................................................. 5 3.1 Advantages: .......................................................................................................................... 5 3.2 Disadvantages: ..................................................................................................................... 6
- Efficiency ................................................................................................................................. 7
- Conclusion ............................................................................................................................... 8
- References .............................................................................................................................. 9
List of Figures
Figure 1. Mercury Arc Rectifier (1922) [1] .................................................................................... 2 Figure 2. World’s first HVDC link between Sweden and the Island of Gotland [2] ...................... 3 Figure 3. HVDC Thyristor Arrangement [4] .................................................................................. 4 Figure 4. Cahora Bassa HVDC System Stretching Between Mozambique and Johannesburg [5] 5 Figure 5. HVDC Cooling System [7] ............................................................................................. 6 i
Abstract
This mini report reviews the history, advantages and disadvantages, and efficiency of High Voltage Direct Current (HVDC) transmission technology and presents a study and analysis on the technology along with current developments. It also speaks on the challenges regarding the
unanimous acceptance of the technology as a viable means of transmission. Introduction
This mini report reviews the HVDC system from its history to its efficiency. It discusses what held the technology which was the mercury arc technology not being ready for use until 1954 which was patented by Uno Lamm, how the silicon thyristor ignited its success, the various advantages and disadvantages such as being able to transmit power across great distances and poses complicated cooling due to additional equipment needed when compared to AC systems, and its greater efficiency when compared to AC system along the same transmission line [1–8].
however, due to technology limitations regarding valves, which are responsible for the conversion of AC to AC and vice-versa, HVDC’s development was held back [1]. Figure 1. Mercury Arc Rectifier (1922) [1] In the late 1920s, the mercury arc rectifier emerged as a potential converter technology, however, it was not until 1954 that the mercury arc valve technology had matured enough for it to be used in a commercial project [1]. 2.2 First Commercial Project – Gotland 1 The first commercial HVDC link, delivered by ASEA in 1954, carried power between the mainland of Sweden and the island of Gotland [2]. Consisting of 98 km of undersea cable between Västervik on the mainland of Sweden and Ygne on the island of Gotland, the project operated at 100 kV [2]. It utilised mercury arc type valves which Uno Lamm, a Swedish electrical engineer working at ASEA at the time, had patented in 1929 [2]. After 25 years of development, Lamm’s invention was ready for commercial use. Initially, the project had a rating of 20 MW [2].
Figure 2. World’s first HVDC link between Sweden and the Island of Gotland [2] The Gotland 1 soon became a test bed for a series of technological breakthroughs in pursuit of developing HVDC [2]. For this, the site is regarded as the most significant heritage site for HVDC development [2]. From its inception, ASEA (later to become ABB) had gained commercial success with its HVDC technology and has remained a world leader in the field [2]. However, its initial success did not go unreserved; as potential customers were concerned about the mercury valves fragility [2]. From history, it can be seen that the complex technology was remarkably robust [2]. ASEA went onto to build 5 more projects at Gotland with the final project from Gotland 1 to the Pacific DC Intertie in the 1970, still utilising mercury arc valves [2]. This pioneering development led to a number of successful projects [2]. However, at the same time a new technology, the silicon semiconductor thyristor, began to emerge as a viable technology for the valves of HVDC systems [3]. The thyristor valve first came into use in HVDC applications in 1970 and from that time forward the limitations of HVDC were largely eliminated [3]. 2.3 Rapid Development of HVDC Technology In 1972, New Brunswick, Canada, thyristor valves were first incorporated into the Eel River project since its inception [3]. It was a back-to-back scheme operating at 80 kV with a 320 MW capacity [3]. 75 schemes with thyristor valves followed and 12 incorporating insulated-gate bipolar transistor (IGBT) valves were commissioned [3]. The projects were carried out by multiple companies, especially ASEA, who make up 60% of the HVDC worldwide market [3]. Other notable companies are Siemens and Areva [3]. The introduction solid-state thyristor ignited the industry, companies involved in this technology still continue to develop and innovate [4]. The
- Due to the proximity effect, hysteresis, eddy current, and the skin effect, DC resistance is lower than AC resistance. DC lines have a less impact on the environment than AC lines [5].
- Voltage source converter (VSC) HVDC systems allow for the interconnection of AC systems with very low fault levels (i.e weak AC system) [4].
- Regarding fault levels of an AC system, DC systems do not contribute to this where rating levels of equipment are a concern [5].
- The HVDC system connecting AC systems do not transfer oscillations from on AC system to another and become cheaper to install than AC systems, depending on power transfer requirements, at 600-800 km [4]. Figure 4. Cahora Bassa HVDC System Stretching Between Mozambique and Johannesburg [5] 3.2. Disadvantages:
- Regarding remote rural areas or electrification loads, along the length of the DC link, power taooffs are more difficult [6].
- There are proposals of multi0terminal DC systems to overcome this problem; however, they are often expensive and will lead to affecting the overall reliability of the DC link as these solutions increases its complexity [6].
- To operate and maintain DC converter stations optimally, a high level of expertise is a requirement. These stations can be placed in different countries resulting in a possibility of contractual, ownership, and operations responsibilities complications [6].
- Compared to AC substations, DC converter stations occupy significantly more space [7].
- Where it would be beneficial to system strength, HVDC infeeds do not add to a network’s fault level strength [7].
- HVDC systems create harmonics, and these harmonics require filtering and pose complicated cooling systems increasing the overall cost [7]. Figure 5. HVDC Cooling System [7]
4. Efficiency
Line losses are superbly lower for DC than for AC [8]. It was found that for a given 2000 km link, line losses for 800 kV DC are about 5 %, while a similar rated AC system of 765 kV sits at about 10 % [8]. For the transmission of comparable amounts of power, the cost of a power line is lower for DC [8]. A HVDC transmission line rated at 6000 MW with a length of 2000 km, only requires one power line coupled with two suspended conductors [8]. The 765 kV AC system above requires three power lines, each with three suspended conductors [8]. The power flow in the line can be
5. Conclusion
It can be seen that HVDC has the potential to meet many future grid system and transmission network requirements which owes itself to lower line loss, greater integrability and achieving long distances, and high transmission efficiency. HVDC is developing rapidly and solves many challenges that traditional AC systems fail to resolve. There are a growing needs for remote and widespread electrical power transmission, particularly in Africa, which is not only capable of transmitting large quantities of power over great distances, but to do it reliably and a less troublesome manner than AC; considering these demands, HVDC can be the future’s transmission technology.
5. References
[1] (^) O. Peake, “The history of high voltage direct current transmission,” Australian Journal of Multi-disciplinary Engineering, vol. 8, no. 1, pp. 47 - 55, 2010. [2] (^) K. S. S. Huq and H. K. R, “A Technical Review on High Voltage Direct Current (HVDC) Transmission,” International Journal of Electrical Engineering., vol. 11, no. 1, pp. 77-85,
[3] (^) O. Vestergaard and P. Lundberg, “Maritime Link The First Bipolar VSC HVDC with Overhead Line,” IEEE, vol. 9, no. 1, pp. 2-7, 2019. [4] P. Tuson, “HVDC strengthening in Southern Africa,” IEEE, pp. 47-50, 2007. [5] (^) P. Kiger, “High-Voltage DC Breakthrough Could Boost Renewable Energy,” NATIONAL GEOGRAPHIC NEWS, 7 December 2012. [Online]. Available: https://www.nationalgeographic.com/science/article/121206-high-voltage-dcbreakthrough. [Accessed 2021 September 11]. [6] “HVDC Transmission,” Allumiax, 11 December 2020. [Online]. Available: https://www.allumiax.com/blog/hvdc-transmission. [Accessed 11 September 2021]. [7] (^) G. Lagrotteria and D. Pietribiasi, “HVDC Cables - The technology boost,” IEEE, pp. 1-5,
[8] (^) Y. Zhu and Q. Guo, “Research on Power Modulation Strategy for MMC-HVDC and LCCHVDC in Parallel HVDC System,” IEEE, vol. 3, no. 6, pp. 2-4, 2019.
