The government’s ambitious renewable energy capacity addition targets will require a significant expansion of transmission capacity in difficult terrain and remote areas. In this regard, surveying can play a crucial role in setting up transmission infrastructure in a timely and cost-effective manner. It can help determine the number of transmission towers required to construct a transmission line across a river and also in selecting the optimum tower foundation based on the topography and type of soil. Further, surveying enables the selection of the shortest possible route for laying a transmission line, which also meets the statutory obligations for clearances.
The conventional methods of surveying include walkover surveys, preliminary surveys and detailed surveys, all of which take a considerable amount of time and manpower. These are manual methods and there is always a possibility that the results do not accurately reflect the details on the ground. On the other hand, modern surveying techniques leverage the latest technologies for mapping and aerial monitoring, and reduce the probability of error.
At the system planning stage, load demand and projected capacity addition are considered for routing purposes. For a reliable, secure and economical power transfer, different voltage levels, routes and connecting points are studied. These factors largely depend on the terrain, and therefore, at this stage primarily forest and physical maps are used, with minimal on-ground surveys. Surveying becomes pertinent at the project feasibility stage, where techno-economic clearance must be obtained. Reconnaissance involving the map study, walkover survey and preliminary survey are conducted. It forms the most important aspect of a transmission line survey as the cost of the transmission line is influenced to a great extent by the route chosen. Next, a walkover survey is carried out on these routes, collecting all relevant information to update the map. After the walkover survey, the most suited route is identified and further studied before conducting a preliminary survey.
The main objective of the preliminary survey is to transfer the route information to the ground and include deviations. At the project execution stage, a detailed survey of the route is carried out. It involves accurately determining the number and types of towers required along with extensions and special towers; the number and types of foundations and special foundations required through levelling, plotting and profiling; final alignment and pegging of locations; trial pit excavations; and detailed soil investigations wherever required.
Light detection and ranging (LiDAR) technology can be deployed for conducting aerial surveys to optimise route corridors for transmission lines and determine the position of towers. It uses laser distance measuring to conduct topographic mapping with the help of aircraft. A key advantage of a LiDAR survey over conventional surveys is the speed of data capture. In addition, the data processed through a LiDAR survey can be directly linked to PLS-CADD. Using this data, models can be created in PLS-CADD to assess the various criteria in relation to the location of transmission lines and towers. Such models can provide the best options for alignments, tower designs and tower positions to develop a least-cost solution. They can also compute and balance the cost against the reliability and performance of transmission infrastructure. Private transmission major Sterlite Grid deployed LiDAR technology for the first time in India for the construction of the Bhopal Dhule transmission project, executed by its subsidiary Bhopal Dhule Transmission Company Limited to conduct topographic mapping. According to the company, LiDAR beams transmitted from aircrafts helped Sterlite function in overcast and cloudy conditions providing high accuracy at a high speed. The risk of project execution came down significantly with the use of these technologies.
The growing focus on the timely delivery of transmission projects pushes developers to deploy aerial technologies such as drones. Drones help increase the uptime of the grid, reduce transmission tariffs, avoid grid blackouts and protect the environment by reducing deforestation along transmission line corridors. Drone-acquired information is highly beneficial for assessing potential site locations, designing site layouts, generating 3D visualisations and making right-of-way estimations. While drone surveys are quite cost-effective, they are difficult to implement because of the need for statutory approvals. Power transmission major, Power Grid Corporation of India Limited, has been deploying drones for the purpose of monitoring faults in transmission lines over various regions. Recently, state utility Kerala State Electricity Board also announced plans to deploy drones fitted with LiDAR for monitoring its high voltage transmission lines.
Going forward, the uptake of these modern technologies is expected to increase as there is greater pressure to deliver transmission projects within strict timelines, lower implementation risks and optimise costs.