Line of duty

Online Editor

Oliver Semling showcases a flagship gas insulated line (GIL) project for high-power, long-distance transmission.

The Jiangsu Nantong Bin Jiang region of China is a major centre for the textile and food industries. With the city expansion and the need for green development, the original overhead transmission line in Nantong City required a complete renewal. This transmission line was one of the earliest long-distance lines, facing increased energy demand and high load, pushing it to its limits. Thus, a massive relocation project incorporating the latest technology was initiated. The gas insulated line (GIL) emerged as an alternative to overhead lines. Stäubli’s customised ML-CUX was used for the busbars in the extensive Bin Jiang GIL pipeline gallery project.

Challenging conditions

GIL systems are increasingly installed to meet the growing energy demand in highly industrialised areas. The Bin Jiang GIL project encountered several challenges, including extreme humidity and temperature ranges. While their design, construction, and installation are complex, GILs offer advantages such as minimal landscape disruption, space efficiency in cities, low electromagnetic radiation, and a safe alternative to overhead lines. In the Bin Jiang GIL Pipeline Gallery project, the original four 220kV high-voltage overhead transmission lines were converted into a shallow underground pipeline gallery, standing at around 1.5m tall. The pipeline’s total length spans approximately 30km, making it the longest line at the same voltage level in China.

The construction of the Bin Jiang GIL pipes encountered numerous challenges, including complex pathways crossing rivers, roads, and difficult terrain like the harbour access road and Yangtze River Road. Pipe jacking, a tunnelling method with minimal surface disruption, was employed to bypass these obstacles and city intersections.

A safe and reliable busbar connector is a key factor for power transmission on the 250kV gas-insulated transmission lines. The pipe jacking spanned approximately 240m, with a maximum inclination of around 10°. Challenging geological conditions and structural hurdles necessitated accommodating large angles and elevation variances in the design.

The Stäubli engineers faced two major difficulties. Firstly, the tolerance range of the spiral spring contacts did not align with the required deflection angle of +/- 5°. Additionally, the GIL design called for a sliding lifespan of several tens of thousands of cycles over several decades. Existing solutions failed to meet these rigorous specifications. By utilising the high-performance and flexible ML-CUX, the GIL design, specifically the pipe-to-pipe connection, achieved high reliability, simplified construction, and extended service life. Moreover, the GIL had to endure high humidity and temperatures ranging from -40°C to 50°C.

A sophisticated solution

The design of the 250kV GIL busbar connector posed challenges in terms of durability, reliability, and safety. To overcome these obstacles, Stäubli engineers developed a connection solution utilising the high-performance capabilities of ML-CUX. Machining and assembly were simplified, and only one ML-CUX unit was required instead of two spiral springs. The chosen solution involved employing an ML-CUX/62N with an approximate diameter of 100mm. This specific configuration offered significant advantages, including exceptional tolerance absorption, the highest power density, low contact resistance, and minimal heat generation. Ultimately, the Stäubli busbar connector outperformed its competitors and successfully passed rigorous on-site tests in China.

The Chinese customer carried out the installation work, with Stäubli Hangzhou (STHZ) providing comprehensive technical support. Established in 1997, STHZ is the first Stäubli Group production site outside the European region. Customer service is a top priority here. In one instance, after a long meeting with colleagues from the Swiss head office, the customer required technical support at the installation site. STHZ promptly analysed and discussed the problem. As a result, their technical support staff drove overnight to the installation site, nearly 300km away from Hangzhou, successfully resolving the issue on-site.

Reduced TCO and more customer benefits

The Stäubli ML-CUX offers several significant advantages, including low installation effort, stable power transmission, and a long life cycle. Another benefit is material savings: during comparative tests with competitors, the ML-CUX exhibited a temperature rise 10% lower than that of its counterparts. This reduction enabled material savings in the longitudinal direction. Additionally, by decreasing the groove depth, material could be conserved in the diameter.

The solution is also demand-driven: the ML-CUX accommodates the design of GIL systems by providing a generous deflection angle, meeting the demands of the market.

Furthermore, it offers the following advantages: low contact resistance and heat generation; high flexibility and compensation for large tolerances and misalignments; high performance and reliability guaranteed by full type testing; and consistent high quality ensured through 100% inspection throughout the manufacturing process.

Overall, these benefits contribute to reducing the total cost of ownership (TCO).

GIL flagship project

GIL solutions have obvious advantages such as high reliability, maintenance-free operation, long service life and comparatively low environmental impact. The Bin Jiang GIL pipeline gallery project provided valuable lessons for future large-scale projects. The Chinese customer recognised the impressive performance of Stäubli’s ML-CUX. The successful collaboration with partners in China establishes a solid foundation for further joint applications in constructing gas-insulated pipelines. Stäubli is already involved in the Chongquing 250kV Chenbao line GIL project.

The Bin Jiang GIL pipeline gallery project serves as a success story for all involved parties and has become a flagship project for the Stäubli Group.

Oliver Semling is with Stäubli Electrical Connectors.

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