An Overview of the Modernization of GIS

  

An entire transformer substation with a 110-kV-GIS; transformers and auxiliary systems are integrated in the sports stadium in St. Gallen, Switzerland.

By Michael Jesberger and Dr. Stephan Pàƒ¶hler, Siemens Energy

The success story of gas-insulated switchgear (GIS), which started to unfold almost exactly 40 years ago, is currently experiencing a new boom. Modern GIS substations seem to be the answer to many of the demands of a growing, power-intensive society.

The worldwide demand for electrical energy is currently increasing by 3 percent each year, some of the reasons being rapid growth in population, higher life expectancy and the trend toward greater urbanization. As a consequence, increasingly large amounts of energy need to be transported into expanding conurbations with the lowest possible losses. One obvious consequence of this scenario is that transmission networks in Europe are now being upgraded from 220 kV to 380 kV. More and more substations are being built in metropolises for the extra-high voltage level over 380 kV. This trend can also be seen in the megacities like Shanghai and Sydney.

Up to the end of the 1960s, only conventional air-insulated substations (AIS) were built in Germany. However, increased voltage levels mean that these substations require huge amounts of space, something that is quickly becoming scarce in populated areas. This is why GIS facilities developed 40 years ago are becoming more important than ever before. Depending on the operating voltage level, GIS substations may require up to 90 percent less space than their air-insulated counterparts. GIS substations are relatively immune to environmental conditions and can be installed in confined spaces, such as public buildings and sports stadiums. They can even be concealed beneath municipal recreation areas (see photos). The substations are continually being developed in line with growing requirements. Modern-day GIS switchgear’s high standards result from the extensive operating experience gathered over the past 40 years coupled with numerous manufacturer-driven innovations.

Innovative design in GIS development has not only resulted in reduced space requirements, but also in the use of less material and SF6 gas, while at the same time permitting enhanced performance. In addition to technical considerations, aesthetics, environmental sustainability, architecture, protected building status and property protection are playing an increasingly important role in substation design. Modern substations must blend into their surroundings and are required to be visually and acoustically imperceptible from the outside. Electromagnetic compatibility (EMC) is also becoming more important. In practice this means that complete high-voltage substations are now being built underground or they are being integrated into building complexes during the construction stage.

An entire transformer substation complete with all auxiliary systems has been integrated in the Dohas town planning concept in Qatar, for example. The transformer substations are equipped with gas-insulated high-voltage switchgear at the 220 kV and 66 kV levels, which will supply energy to the Westbay district (see photo, page 28).

Age-related Replacement

Whereas new networks are being built to cope with increasing energy requirements in emerging economies, the age-related need for replacements in industrial countries and the efficient integration of regenerative energy sources are also gaining in importance. According to EU Commission estimates from 2005, the average age of the installed infrastructure in Europe is between 30 and 40 years. Safety, efficiency and environmental sustainability requirements coupled with increased network requirements will prompt upgrades and extensions to many transformer substations over the next 10 years. These will result in an increase in overall power supply system reliability and will improve levels of personal safety during operation.

Network expansion on GIS design is based on two concepts: First, existing GIS switchgear can be extended using the latest technology and, secondly, existing AIS switchgear can be replaced by space-saving GIS switchgear. With the exception of changing technical parameters, such as rated current or short-circuit current, no technical reasons currently exist for replacing installed GIS switchgear, as these systems can be extended using series-production GIS components. This concept is to retain the equipment, as installed GIS switchgear will not be approaching the end of its service life in the near future.

GIS substations can be installed in confined spaces. The complete transformer substation inclusive a 69-kV-GIS is being built under a park in Anaheim, Calif.

The combination of gas-insulated and air-insulated designs, known as hybrid design or mixed technology, can also result in considerable space savings. In such cases, the main components, such as circuit-breakers, current and voltage transformers, disconnectors and earthing switches, are implemented in gas-insulated technology and connected to the air-insulated bus via overhead conductors in outdoor bushings. Thanks to the modular concept of gas-insulated components, almost all switchgear configurations can be implemented based on a hybrid design. Today’s requirements (higher voltages, larger amounts of energy, environmental sustainability) also have made it necessary to find new solutions for energy transmission paths.

Gas-insulated Transmission Lines

The gas-insulated transmission line (GIL) provides a transmission path solution. It consists of an aluminum conductor tube and an aluminum enclosing tube filled with an insulating gas mixture. It can transmit power capacities up to 3000 MVA. Wherever special solutions are required, GILs are an economically and ecologically viable alternative. Compared to other energy transmission systems, transmission losses are lower and electromagnetic field emissions are reduced by up to 90 percent. GIL’s encapsulated design means that the lines can be installed above ground or in tunnels, and can even be buried directly underground.

An entire transformer substation complete with all auxiliary systems has been integrated in a parking garage in Dohas, Qatar.

Siemens recently secured its first contract for an underground GIL from RWE Transportnetz Strom. As part of the power supply system expansion in the German Frankfurt region, the plan was to convert the Kelsterbach transformer substation, situated directly alongside the autobahn and opposite Frankfurt Airport, from 220 kV to 380 kV and integrate it into the 380-kV transmission network.

RWE Transportnetz Strom began operating the new 380-kV switchgear, which is of compact gas-insulated construction, at the end of 2007, replacing the previous 220-kV outdoor installation. It plans to connect the switchgear to the 380-kV system in second quarter 2010 at the latest.

Diagram of GIL-project Kelsterbach.

Because the space necessary for a high-voltage overhead line is not available—due to a new runway that will be built northwest of the airport—the incoming lines must be laid underground over a distance of nearly one kilometer. Beyond the terminal tower, the overhead transmission lines are routed via bushings into the GIL. The GIL is laid directly in the ground, in much the same way as a pipeline, and leads directly into the GIS, which is located some distance away.

Covering a route distance of about 900 meters, the Kelsterbach system with its two three-phase tubular systems represents the longest length of buried GIL installed by Siemens to date (see diagram above). About 500 individual modules will be delivered and welded together on site to implement the 5,400 meter long single-phase tube. The GIL modules have been installed and laid in the ground along the planned route since May 2009. The transmission line is due to be connected into the system early this year. Each of the two GIL systems has a transport capacity of 1,800 MVA (permanent load) in operation.

Finally, besides space problems and increasing power requirements, official approvals and public acceptance are becoming increasingly important in the construction of power supply installations.

In the past, for example, substations were erected as purely functional structures for permitting infrastructure development, today’s space-saving high-performance solutions, such as GIS and GIL, meet a variety of environmental requirements with maximum flexibility.

Modern GIS switchgear is compact, flexible and efficient in use. Reduced energy demand during production, sustainable resource utilization, in addition to low life cycle and maintenance costs, all combine to make GIS systems a sound investment for the future. They can make an extremely valuable contribution to power supply performance, quality and reliability.

Poehler is director, transmission for European projects under the umbrella of high voltage substations/GIL.

Jesberger is chief executive officer, high voltage substations.

On the “ËœNet: http://siemens.de/energy

 

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