In order to deliver the growing power demand in the country, there is a need to establish a strong transmission and distribution network and adopt appropriate testing and measuring solutions to maintain a robust power grid. The transmission line length in India grew at a compound annual growth rate of around 9 per cent between 2016-17 and 2021-22 to stand at 458,258 ckt. km (220 kV and above) as of May 2022, resulting in increased demand for transmission infrastructure and equipment including towers. Transmission tower testing is important for determining the dependability of towers in adverse weather conditions and ensuring their compliance with various standards and regulations.
Several tower manufacturers and approved government labs have established dedicated transmission tower testing facilities for commercial as well as research and development (R&D) purposes. Some of the common tower testing techniques are full-scale prototype testing that simulates various variables and conditions, real-time strain gauge monitoring of member loads, and reliability tests. There has also been a growing uptake of more sophisticated and advanced tower testing solutions.
Testing methods
In a traditional proof test, the design conditions are verified, only static loads are applied, the support has level-fixed foundations, and the restraints at the load points are the same as in the design model. If a proof test is ordered, it should be done on a full-size prototype structure or another tower of similar design before it is manufactured at scale. This kind of test will assess the ability of the towers and their connections to withstand design
loads specified for a structure under controlled conditions. Another function of proof tests is fit-up verification. However, the test cannot completely assess how the tower will respond to dynamic loads, if the foundations are not ideal, and the issues associated with connected wires at the load points.
The transmission line industry tests the prototypes of structures. These tests provide a higher level of structural reliability for transmission line structural systems. There are a number of other important reasons to perform tower tests. One of the key reasons is to justify and calibrate tower designs to the specific transmission design codes. Another advantage of testing is the complete assembly of the tower, which provides an insight into the fabrication details. A successful test also provides a level of confidence along with a computer model to design the tested tower and its combination of bodies and legs. A tower test can also be used during transmission line upgrades.
Test facilities in India
There are less than a dozen tower testing stations in India and hence tower manufacturing companies with a forward integrated presence in both transmission tower erection and transmission tower testing are more capable of timely realisation of transmission deliverables than their global counterparts. The Central Power Research Institute set up the first transmission tower testing station in 1976. This station is still open for commercial as well as R&D tests. Among the initiatives undertaken by private players, Larsen & Toubro’s digitally driven, green tower manufacturing units at Puducherry, Pithampur and Kancheepuram have a combined capacity of more than 150,000 tonnes of tower components per annum. The tower testing and research station at Kancheepuram is amongst the most renowned testing centres in the world. The clientele of this testing facility includes utilities from 30 countries.
KEC International is another private major that has developed significant tower testing stations in India – Maharashtra, Rajasthan and Madhya Pradesh. These world-class facilities are located in close proximity to our manufacturing plants and provide complete testing solutions for all kinds of transmission towers of up to 1,200 kV, including lattice and guyed towers, tubular and monopoles. During the pandemic, the company commenced virtual tower testing at the Butibori testing station, which allowed customers across the globe to verify design and quality parameters of towers through live video streaming. Also, Kalpataru Power Transmission Limited has developed a tower testing and R&D station, equipped with sophisticated and state-of-the-art equipment. It has the capacity of testing double-circuit towers up to 800 kV and single-circuit towers up to 1,200 kV, with 30×30 metre base width and 85 metre height.
The facility has an annual testing capacity of 1,800 mt of transmission and distribution towers and poles. This testing station and R&D centre has been recognised by the Department of Scientific and Industrial Research, Government of India.
The way forward
Transmission tower tests assess tower’s quality, longevity and installation procedure, helping transmission businesses mitigate RoW and land acquisition challenges. Furthermore, tower testing stations assist transcos in testing prototypes and towers of various specifications, allowing them to construct economically feasible transmission towers that meet the tender’s specific technical criteria. The demand for transmission tower testing is expected to rise due to the expansion of transmission infrastructure and the ever-increasing need for technical accuracy and quality excellence. In India, there are relatively few testing stations in comparison to actual tower installations, which presents a huge opportunity. Thus, the number of testing sites is likely to increase in the medium future.