How L&T Navigated the Intricacies of High-Altitude Environments
Constructing substations in the Himalayan Ranges
When we envision places of high altitudes, such as the majestic Himalayas, what springs to mind? Picturesque landscapes with rugged terrains, snow-covered peaks and cascading waterfalls, right? Absolutely!
Embarking on projects amidst high altitudes poses unique challenges. In this article, we delve into how L&T, with its wealth of experience, has successfully tackled such challenges.
L&T’s Power Transmission & Distribution (PT&D) business vertical boasts a remarkable track record of constructing substation projects in the awe-inspiring Himalayan Ranges. In places such as Wangtoo and Lahal in Himachal Pradesh, the gas insulated substations (GIS) were built at an impressive altitude of 1,700 meters above the mean sea level (MSL). Additionally, L&T has executed numerous substation projects in Nepal, spanning the Koshi corridor at Basantapur and Baneshwar, where altitudes range from 1,500 meters to 2,500 meters above MSL.
Navigating the challenges
Image 1 depicts the rugged terrain, high altitudes and extreme weather conditions of the Himalayan Ranges. One can imagine the numerous challenges involved in constructing substations in such places. These challenges can be broadly categorised into electrical and construction/design aspects.
Electrical challenges
- Insulation strength. In most electrical equipment, air serves as insulation between live to live and live to earth components. Therefore, for air-insulated equipment, the insulation strength relies on the dielectric properties of air. At greater altitudes, where air pressure decreases, the air becomes thinner, leading to a reduction in insulation strength. Standard electrical equipment available in the market is typically designed for altitudes up to 1,000 meters above MSL. Consequently, every piece of equipment must be redesigned when the location exceeds 1,000 meters MSL. This results in larger equipment sizes, and specific clearances between live lines and live to earth connections must be calculated for the particular altitude.
- GIS design. Substations can be classified into two types: air-insulated substations (AIS) and gas-insulated substations (GIS). In AIS, the equipment remains exposed to the atmosphere, with air serving as the insulation medium. Conversely, GIS houses the entire substation equipment, including the bus bar, within a pressurised SF6 gas enclosure, acting as insulation between live components and live to earth connections. In mountainous regions, GIS is often preferred due to its smaller footprint requirement, which is approximately one-tenth of the footprint that AIS needs.
- Altitude correction factor. In GIS, although the majority of the substation equipment remains within gas-filled enclosure and is not exposed to the atmosphere, certain portions, such as incoming lines, related equipment connections and transformer connections, are exposed. Thus, such equipment needs to be suitably designed to withstand the altitude conditions of the area. The reduced oxygen levels and thinner air at higher altitudes also impact the efficiency of diesel engines. Therefore, when sizing diesel generator (DG) sets, it is crucial to take into account altitude correction factors to ensure the desired output.
- Effect of subzero temperature and snow. Similarly, subzero temperatures can hamper battery performance, making it necessary to implement heating systems to maintain battery functionality. Additionally, the presence of snow deposits must be factored in when designing conductors and structures to withstand the added load.
- Earthing systems. Another significant challenge lies in earthing systems. In mountainous regions at higher altitudes, soil resistivity tends to be exceptionally high. Given the criticality of the earthing system for substation safety, both for equipment and personnel, various mitigation measures must be employed to address this issue.
Construction Challenges
- Challenging terrain. It is important to note that for substation construction, the ideal land profile is flat with minimal variations in level. However, in hilly terrains, such flat land is seldom available. The best option is to excavate the area, striving to make the land as flat as possible. Nevertheless, due to the need to accommodate various substation buildings in a single location, extensive excavation can prove to be impractical and costly. To address this, different benches or terraces are created along the slope profile, allowing for different buildings at different elevations. Refer to Image 1 for a visual representation of these benches.
- Stability and landslides. The steep 1V:1H slope profile of the land in many substation projects poses significant challenges during the construction of facilities such as the substation building, transformers and auxiliary buildings. As several areas are prone to landslides in the Himalayan Range, stability analyses must be conducted at each design stage, which are scrutinised carefully with the assistance of geotechnical experts. With elevation differences ranging from 6 to 12 meters, RCC retaining walls are constructed to support the terraces. However, electrical clearances must be considered while designing the electrical connectivity between equipment located on different benches.
- Approach roads. Considering the heavy vehicular movement required for transporting power transformers, well-designed approach roads are crucial. Easy access roads play a vital role in facilitating the transportation of all electrical equipment.
- Extreme weather. Meticulous calculations and structural loading must account for factors such as ice load, which increases the weight of structures to withstand low temperatures. Heavy snow deposits during winter can create additional problems, including restricted movement in the area, which can impact the construction schedule. Advanced planning is necessary to consider these factors and ensure the timely completion of projects. During summer, the melting snow can cause water to flow through the substation land, adversely affecting the construction process. It is essential to devise appropriate diversion plans to address this issue. Additionally, while designing stormwater drains, these aspects should be considered to provide a permanent solution.
Achieving success in high-altitude substations
By dealing with these challenges effectively and consistently, the PT&D vertical of L&T has established itself as a leader in overcoming high-altitude obstacles. Through a combination of innovation, engineering expertise and meticulous planning, L&T has successfully transformed the once-daunting task of constructing and operating substations in the treacherous terrains of the Himalayas into a resounding success story. L&T has consistently completed all high-altitude substation projects within the designated timeframes, setting the bar very high indeed.
This article is written by KK Jembu Kailas.
KK Jembu Kailas is the Lead Subject Matter Expert in Electrical and Electronics Engineering at L&T Edutech. He has over 36 years of experience in power system engineering, industrial electrification and electrical substation engineering.
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