Respecting the environment

Transcription

1 MAIN FEATURE CHAPTER I RESEARCH WITH AN EYE ON THE FUTURE Respecting the environment Low power losses and a lesser visual impact on the landscape make Gas-Insulated Lines (GIL) a very environmentally friendly transmission solution compared to overhead lines. Alstom Grid s eco-design makes them even more so. Power electronics also have great environmental credentials as distributed energy sources become more widespread. Meanwhile, ester oils have proved their value in distribution transformers; research is now focusing on overcoming the challenges to their potential for power transformers. 12 Alstom Grid///Summer 2010

2 Encapsulated in a 400 to 600 mm diameter metallic case, Gas-insulated Lines bear a resemblance to pipelines. Gas-Insulated Lines (GIL): choices today and tomorrow Thanks to their high transmission capacities and reliability, GIL have been in use alternative to cables or overhead lines in a growing number of applications. ing from a few meters to 900-1,000 meters. Directly laid on the soil or in trenches or tun- widen (and lengthen) to stand-alone installations up to several kilometers for resolving right-of-way issues. GIL provide an effective technological answer to the increasing energy needs of our urban society and to the extension and reinforcement of the present electricity transmission and distribution networks. Transmitting bulk power over short and long Gas-Insulated Lines are a transmission technology developed in the late 1960s for use in substations, hydro power plants, underground facilities, and so on. Their high transmission capacity (up to 3,000 MVA through one GIL circuit) and multiple advantages for transmitting bulk electric power in such complex sites. In substations, for instance, GIL serve as connections between GIS switchgear and power transformers or overhead lines, at distances rangdistances in a safe and environmentally friendly way represents one of the major challenges of the coming decades; GIL is a key to solve this issue. Electric pipelines Encapsulated in a 400 to 600 mm diameter metallic case, Gas-Insulated Lines bear a resemblance to pipelines. Originally developed for GIS connections, GIL have similar bus sections and busbar arrangements. The electric pipeline consists mainly Alstom Grid///Summer

3 MAIN FEATURE CHAPTER I RESEARCH WITH AN EYE ON THE FUTURE The T155 Gas-Insulated Substation installed at Shuqaiq, Saudi Arabia, a major Alstom Grid reference demonstrating that the company can of a pair of tubular aluminum coaxial conductors, the inner one being at the high voltage level and the outer one being earthed. To ensure insulation, the space between the enclosure and the conductor 6 ) or a pressurized gas mixture of nitrogen and SF 6. With their very high conductor crosssection, GIL are designed for high transmission capacities with rated currents typically reaching 4,000 A at 550 kv, and a shortcircuit current capability up to 63 ka, explains Mathieu Bernard, GIL Project Manager. This offers multiple advantages: GIL combine low capacitance (and therefore very low transmission losses), high reliability, and operational safety thanks to a robust casing and the fact that they are long lifetime up to 50 years with virtually no material ageing. Moreover, thanks to route capabilities, GIL are adapted to solve complex geographic installation issues like hydroelectric power plants in new or existing underground conditions, Bernard adds. One drawback, however, is their cost, which is still relatively high when compared to seven times more expensive). In fact, GIL are not designed to compete with overhead lines everywhere but rather as a means of power transmission where OHL cannot or must not be applied. High service continuity ago, more than 250 km of three-phase GIL systems have been installed in the world (750 km of single-phase pipes). They operate at different voltage levels between GIL combine low capacitance, high reliability and operational safety kv and 800 kv (mainly at the 420 kv level), and demand has significantly increased over the past few years. At Alstom Grid alone, over 50 km of three-phase circuits have been installed or ordered since the beginning of GIS production, including 30 km over the last 12 years, showing clear acceleration. Almost maintenancefree and with low operating costs, GIL are now widely recognized as a well-proven technology with a long service record and a high level of reliability. Even so, modern digital monitoring systems help further improve their reliability and service continuity, says François Biquez, Senior Expert R&D Manager for transmission enable the real-time monitor- 14 Alstom Grid///Summer 2010

4 ing of parameters such as SF 6 or gas mixture density, SF 6 leakage trend analysis, temperatures in compartments, partial discharges, internal arc localization and detection, etc. Abnormal conditions that could lead to potential failures are therefore rapidly detected. As a result, safety for personnel and switchgear is enhanced, as well as security and quality of power supply, protection of the environment (against SF 6 leakages), asset management (maintenance and outage planning, integration in a digi- due to energy deregulation requiring more rapid and accurate data management, and so on. On the other hand, today s computerized design tools offer the ability to adapt GIL to severe operating conditions. For each particular installation, calculations can be made to select the right solution and ensure optimal working conditions while adhering to strict regulatory standards. The dimensioning of a GIL clearly depends on its dielectric withstand performance and on its thermal capability to carry the rated current, explains Biquez. As the thermal limits of the product are affected by the way the GIL is installed, computer simulations are necessary to decide on the appropriate design. In the case of an underground hydro power plant, thermal simulations have enabled Alstom Grid s designers to evaluate the thermal behavior of the GIL enclosure as a function of the tunnel height, or to compare the conductor and enclosure temperature distribution depending on whether the GIL is placed in a horizontal tunnel or a vertical shaft. Opting for a GIL solution brings major envi- to a very low capacitance, the electrical resistance and power losses of GIL are extremely reduced up to 70 percent lower than M O R E Alain Girodet TECHNICAL BENEFITS OF GIL COMPARED WITH CABLES AT HAMS HALL The 420 kv Hams Hall substation in the West Midlands, England, required a new connection to reinforce the network. However, existing overhead lines and buried cables and pipes demanded that the connection be in trenches at the one end and above ground at the other end. Both GIL and cables offered suitable solutions. However, for both technical and economic reasons, the British utility National Grid adopted the Alstom Grid GIL solution. A continuous current rating of 3,190 A would have required two cables with two outdoor terminations per phase compared with one GIL, says Alain Girodet, Senior Expert, Alstom Grid High Voltage Technology and Materials Manager. Cable junctions would also have been more of an issue from a dielectric perspective, he adds. To minimize environmental risks with GIL, an insulating gas mixture made of 20 percent SF 6 and 80 percent N 2 was chosen, as well as a totally welded pipe design (which required special care in the assembly process to avoid weld slags seeping inside the GIL). Another advantage is that the N 2 /SF 6 mixture can be easily separated and recycled after use. HIGH SERVICE CONTINUITY Alstom Grid///Summer

5 MAIN FEATURE CHAPTER I RESEARCH WITH AN EYE ON THE FUTURE those of overhead lines (OHL). This means less waste of energy, and no need for reactive compensation for lengthy GIL, contrary to long cable connections. Another advantage is a lower visual impact on the landscape, suggesting that GIL may be a realistic solution in sites where OHL would be banned. A costly solution, indeed but the expense may be worth it, one chief executive of a U.S. transmission company nitely expensive if their construction is resolutely opposed by local communities. To minimize the environmental impact of its GIL solutions, Alstom Grid has implemented an eco-design approach, as for a number of its products. The latest designs are nowadays completely optimized in a sustainable development perspective. The whole life of the product is considered, from cradle to grave. It starts with a life cycle encountered when manufacturing and using the GIL, from raw material extraction and transportation to the disposal of the product at the end of its life. Up to 16 indicators are used, showing the impact of the various steps of the product life cycle on features such as global warming, ozone toxicity, hazardous waste, amount of slag/ ashes, etc. Each component of a GIL may then be optimally designed to achieve contributing to a moderate and responsible use of the needed resources, and ensuring a high recyclability rate. The latest developments have led, for instance, to a more environmentally friendly insulation medium: the amount of greenhouse effect SF 6 gas produced has been dramatically reduced through the use of a g as mixture based on percent of nitrogen and the rest of SF 6, says Biquez. Alstom Grid was also able to optimize the section of the conductors, enabling the GIL to exhibit lower heat losses compared with OHL and HV cables. Ensuring safety for people As high voltage power transmission lines even in crowded public areas, the safety of the surroundings is essential. Thanks to the design of their aluminum enclosures, GIL completely exclude the risk of explosion. materials (such as oil) makes the GIL abso- even in the case of an electrical fault; the GIL will even play the role of a buffer or and a GIS, thus preventing the fire from spreading and allowing the rest of the system explosion-proof characteristics, GIL can be installed in shared infrastructure like road and rail tunnels, open public areas, etc. An illustration of an in-public area installation of a GIL is the Hams Hall project in the U.K., which was energized in 2004 (see sidebar). radiation emission. Cross-bonding of singlephase enclosures allows the return current to pass through the enclosures. This creates a screen effect that provides the GIL with a lower magnetic field radiation compared with alternative solutions such as cables and OHL. Computer calculations show that mag- phase GIL system (operating at 550 kv and 4,000 A) are lower than 250 μt, half the exposure limit for workers set by the European Union directive. At a distance of 1 meter to the enclosure, the value drops to 10 μt, less than one-tenth the emission of buried XLPE cables 1 meter above ground level, and less than a quarter of overhead lines (below the lines at 1 meter above ground level). In fact, GIL enclosures can even be safely touched. M O R E Gerhard Seyrling INTERVIEW WITH GERHARD SEYRLING, SENIOR VICE-PRESIDENT INNOVATION & STRATEGY What is Alstom Grid s experience with GIL? Alstom Grid has long experience with GIL design and installation, especially for large power sites. One of our major references is the PP9 project in Saudi Arabia: with total circuit lengths of approximately 5.6 km, more than 17 km of single-phase enclosures were necessary. Alstom Grid has developed and masters a whole range of or welded connections and various insulating gas mixtures to optimize cost, performance, reliability and environmental protection. How can GIL compete against overhead lines and cables? GIL have proved their ability to respond to any installation constraints as well as carrying high power ratings without requiring multiple circuit overhead lines, the major advantage is better integration in the urban environment and landscapes. Compared with cables, GIL can transmit greater quantities of energy: 3,000 MVA can be transmitted through one GIL circuit while two circuits would be required for the alternative HV cable solution; this performance has a direct impact on price, footprint and right-of-way requirements. What are customers looking for? Besides substations, answers to two types of issues. One is carrying high rated currents in urban areas where OHL are prohibited; the other is to ensure regional and international bulk power connections with GIL offering powerful solution through tunnels, bridges, and so on. 16 Alstom Grid///Summer 2010

6 Alstom Grid has installed (or received orders for) more than 50 kilometers of 3-phase GIL systems since the beginning of GIS success are the Jebel Ali power plant in the United Arab Emirates, Shuqaiq in Saudi Arabia, and the Hams Hall substation in the West Midlands, U.K. Alstom Grid///Summer