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Aerial Technologies:Gaining popularity in power transmission segment [free access]

March 14, 2017

According to Global Transmission Research estimates, the global high voltage transmission line network comprised around 4,112,200 km of 110 kV and above lines at the end of 2015. Of this, the overhead line network is estimated to be around 4,030,000 km. Another 1,352,000 km of high voltage network is proposed for development over the next 10 years up to 2025, the majority of which will be overhead lines. This vast existing and future network traverses a range of environments, climates and terrains. This poses several challenges during project execution as well as in maintenance during the useful life of overhead lines as they are subject to storms, ice, rain, humidity and atmospheric corrosion. World over, utilities are now considering new solutions to reduce costs, improve safety, and increase the reliability of their transmission systems.

 

In this context, the application of aerial technologies in transmission is gaining popularity in both project execution and for operation and maintenance (O&M) of existing networks. Advanced technologies like helicopter stringing and tower erection, light detection and ranging (LiDAR), sky crane and unmanned aerial vehicles (UAVs) or drones are used in planning, design and construction of overhead transmission networks. Their deployment ensures faster implementation without compromising on safety and reduced costs in several cases. Further, given the long time period involved in the execution of transmission projects, including long-drawn clearance procedures, using the right technologies could shorten the design and execution time resulting in overall savings to the developer and the public.

 

For O&M activities, utilities are deploying various aerial techniques such as hot line washing and live line maintenance using helicopters, LiDAR surveys, as well as using UAVs to perform line inspections and maintenance, storm damage assessments and vegetation management. The available aerial technologies offer a more effective and accurate means to undertake regular preventive and predictive maintenance of transmission lines to preserve the lines in proper operating condition. Further, this has gained significance as utilities have to adopt measures to extend the useful life of lines (a large part of the existing networks in Europe and North America were built in the 1960s and 1970s), increase electrical energy transmission capabilities, prevent failures, and ensure employee and public safety.

 

According to industry estimates, the global annual revenue of drones and other robotic technologies used in transmission and distribution (T&D) systems are expected to increase multifold to USD4.1 billion in 2024 from USD131.7 million in 2015. Further, a global investment of USD16.2 billion is expected in drones and robotics technologies for T&D systems up to 2024.

 

Applications in project commissioning

By deploying advanced aerial technologies in project commissioning, transmission system developers are able to speed up project execution as well as reduce implementation risks to a large extent. This results in early revenue inflow from the project.

 

Several transmission lines in the US have been laid using helicopter stringing. For instance, FirstEnergy Corporation, as part of its USD4.2-5.8 billion ‘Energizing the Future’ initiative aimed at strengthening transmission infrastructure, has been using the helicopter method to replace existing lines to enhance system reliability. Besides replacing existing equipment with advanced technologies, the other factors driving this investment are meeting projected load growth propelled by shale gas-related activity and other development in the region and undertaking system reinforcing to cope with power plant retirements. Some of the lines that have been replaced using helicopters under the project include 114.5 miles (184.27 km) of the 345 kV Bruce Mansfield Plant (Pennsylvania)–Glenwillow (Ohio) transmission line, the 7-mile (11.27-km) Adams–Pine line, and 7 miles (11.27 km) of wire on a 69 kV transmission line in Pittsburgh's North Hills district. Xcel Energy and Great River Energy also used helicopters for stringing the 240-mile (386.4-km), 345 kV Fargo–St. Cloud–Monticello line, which is part of the Capx2020 project.

 

France’s transmission system operator Réseau de Transport d´Électricité (RTE) regularly uses helicopters for stringing of transmission lines as well as erection of pylons. In fact, it has a separate aerial division, Services et Travaux Héliportés (STH), which is responsible for the surveillance, maintenance and construction of the network via a fleet that includes H225, AS355, H135 and H125 helicopters.

 

In India, Sterlite Power Transmission Limited (SPTL) became the first private transmission company to use aerial technologies such as helicopter stringing, LiDAR surveys and sky crane to design and construct its projects. It used the LiDAR technology to conduct topographic mapping with the help of aircrafts for its Bhopal Dhule transmission project. It also adopted helicopter stringing for the 765 kV Bhopal–Indore and 400 kV Bhopal–Bhopal lines. This helped to reduce the transmission line shutdown time, resulting in minimal disturbance to the local community and the environment. Transmitted from the aircraft, LiDAR beams helped the company to function in overcast and cloudy conditions providing high accuracy at high speed.

 

In another first in the country, SPTL deployed an air crane to set up a power transmission line in the mountainous terrain of Jammu & Kashmir as part of the Northern Region Strengthening Scheme XXIX (NRSS XXIX) project. It partnered with US-based Erickson to install transmission towers in the tough Himalayan ranges of Pir Panjal using a S64 Aircrane, which is a heavy lift helicopter. This will help SPTL drastically reduce project execution time and commission the NRSS XXIX project ahead of schedule. It has already commissioned the project’s first phase—the 400 kV Jalandhar–Samba line—12 months ahead of schedule. The second phase includes the Samba–Amargarh line and is currently under construction.

 

Applications in O&M, repair and vegetation management

To increase efficiency in maintenance, power line companies undertake manual detection from helicopters to spot trees that pose a risk to overhead lines. Helicopters are also used for hot line or live line maintenance, which is preferred by utilities as it does not require the line to be offline during maintenance activities, thus avoiding outages and service interruptions. In contrast, cold line maintenance/washing involves taking the line offline, leading to significant revenue loss for the transmission utility and customer dissatisfaction due to the resultant service interruption. Hot line washing can be done to clean insulators for up to 400 kV lines. Under this method, a high-pressure (300-800 psi) jet of de-mineralised water is released in the air. The water particles thus released split due to air resistance, making the water path non-continuous and offering sufficient electrical resistivity of more than 30,000 ohm-cm. The water used for hot line washing should have conductivity of less than 200 micro mhos per cc to avoid leakage of current.

 

To resolve vegetation management problems and to identify line defects, a more modern approach is to use manned helicopters equipped with LiDAR to scan overhead lines. This approach is also far more accurate than manual detection, thereby helping to reduce service interruptions and improve service quality. This method is being used widely for scanning and planning high voltage transmission networks across North America. However, using manned helicopters extensively for power line inspections is very expensive, and can cost over USD100 per km, depending on the data capture and quality requirements.

 

France-based energy company Électricité de France began using manned helicopters for maintaining and repairing transmission lines in as early as 1990. RTE oversees 105,000 km of transmission lines aerially across the country through its STH division to detect faults and undertake maintenance work. It undertakes visual and thermal inspection using helicopters. Notably, RTE through its STH division owns a fleet of 13 light and 2 heavy helicopters and is constructing a new site at Avignon airport to house all its airborne facilities from 2017.

 

India’s high voltage network developer Power Grid Corporation of India Limited (PGCIL) uses helicopters for aerial patrolling to optimise manpower requirement and time management, and improve efficiency in maintaining the lines. In August 2016, it commenced works on a project to conduct aerial patrolling of 17,000 route km of transmission lines in the northern region. It has also started using helicopters equipped with LiDAR, thermovision cameras, corona cameras, HD video and image sensors to identify major defects like tree infringement, damage to foundation, broken insulators or pollution on insulators, conductor defects and hotspots.

 

Many US-based transmission companies such as FirstEnergy Corporation use helicopter patrols to conduct transmission line inspections as part of their ongoing efforts to enhance service reliability. In fact, the use of LiDAR in network maintenance has increased in North America particularly since the introduction of the NERC FAC-003-3 reliability standard in July 2014.

 

Use of UAVs in electricity transmission

An emerging and promising technology is the use of UAVs for power line inspections and repair. UAVs are capable of performing fully robotic operation. They have a built-in video link with the operator, a high precision inertial measurement unit, a multi-global navigation satellite system receiver and an integrated multi-sensor system, along with an on board computer and storage unit. A consolidated UAV patrol provides increased efficiency as a single survey flight enables data capture for the needs of network planning, engineering, maintenance planning, vegetation management and fire threat analysis, thereby reducing costs and the need for a routine patrol cycle. The technology will help in improving the reliability, resilience and safety of the transmission networks.

 

Several transmission system operators across the world are conducting research and limited demonstration projects with UAV and robotics. In 2014, UAVs were deployed in Finland to collect essential inspection data for vegetation clearance and component maintenance planning of power lines. The collected LiDAR data was very helpful in determining the vegetation clearance needs. In addition, the visuals of components such as isolators, conductors and transformers collected by the UAVs were of a higher resolution than those collected using manned helicopters in the same area. In the same year, San Diego Gas and Electric became the first utility company in the US to use UAVs [after obtaining approval from the Federal Aviation Administration (FAA) to use drones] to inspect transmission lines. It deployed them in the rural areas of San Diego County.

 

Thereafter, others like PPL Electric Utilities, Florida Power & Light, Arizona Public Service Company and PG&E obtained FAA authorisation to use drones to assist with inspections of electric infrastructure. In November 2015, PPL Electric Utilities assessed the feasibility of implementing the technology to perform routine line inspections on its overhead power lines and substations in its service area in Pennsylvania. PG&E, in May 2016, conducted two separate test projects to ascertain the feasibility of using drones to monitor transmission infrastructure in remote areas and to detect methane leaks across its service area. PG&E is also working with NASA’s Jet Propulsion Laboratory among others to test NASA’s open path laser spectrometer sensor on a drone. The utility expects drones to play a vital role in future gas leak detection and in storm and disaster response.

 

More recently, in February 2017, Minneapolis-based Xcel Energy entered into a ‘partnership for safety plan’ agreement with FAA to research the safe operation of UAVs for inspecting critical infrastructure, particularly the utility’s transmission lines across 10 states. The utility has previously worked with FAA to develop UAV guidelines for the energy sector and conducted several pilots using drones. Xcel Energy also partnered with North Dakota for a research project involving use of UAVs to assess damage after severe weather conditions. In Nevada, NV Energy along with its partner Nevada Institute for Autonomous Systems, in November 2016, completed an unmanned aircraft system (UAS) pilot programme to inspect, collect and analyse data on sections of the utility’s T&D lines.

 

It may be noted that FAA is yet to finalise regulations on commercial use of UAVs, which are expected in spring 2017. Until such rules are finalised, the FAA provides authorisation for commercial use through the Section 333 exemption process. Under this exemption, UAVs must fly less than 400 feet above ground and follow line-of-sight restrictions. Further, only certified FAA pilots can operate commercial UAVs. However, the final FAA regulations are expected to remove this restriction, which will allow line workers to operate UAVs after receiving appropriate training. While line-of-sight restrictions are applicable, an investigation is ongoing to demonstrate and develop commercial UAS beyond line-of-sight flights for electric companies. For instance, Edison Electric Institute and Sharper Shape are undertaking research in this area.

 

In Europe also utilities are using drone technology for infrastructure inspection and data collection. On the regulatory front, the European Aviation Safety Agency (EASA) has been working on providing European Union (EU)-level regulatory clarity for operation of UAS in various civil applications. In December 2015, EASA released the technical opinion, which provided 27 concrete proposals for a regulatory framework for operating all UAS and established three categories of operation—open, specific and certified—with different safety requirements, each proportionate to the risk. Thereafter in August 2016, EASA issued prototype regulations for the open and specific categories. The agency foresees significant growth of the drone sector and predicts that the EU will be the second biggest market for drones in 2020. The EU is reviewing these regulations and the final regulations on UAS are expected by the end of 2018, providing a common legislative framework for the operation of drones.

 

Meanwhile, individual EU countries have their own regulatory frameworks for the operation of drones. For instance, in France, one general rule is that UAS must stay within the pilot’s line-of-sight, similar to the regulation in the US. For particular activities, operators have to make a declaration to the civil aviation authority, which has to be renewed every two years. RTE lists the use of drones to maintain ultra-high voltage lines as one of its innovation priorities. Germany and the UK also have their own aviation authorisation procedures for the use of UAS for commercial purpose.

 

Drones are being tested in other parts of the world as well. For instance, in Australia, Transgrid, which operates in New South Wales, tested its own UAV for various applications following the issuance of a license by the Civil Aviation Safety Authority (CASA) in late September 2015. It found that inspections of line defects, substation and building condition assessments and easement clearances can be performed by the UAV.

 

In India, after obtaining the requisite clearance from the Director General of Civil Aviation (DGCA) and the Ministry of Home Affairs, PGCIL commenced patrolling of the ±500 kV Balia–Bhiwadi high voltage direct current (HVDC) line using UAVs from April 2016. These UAVs are equipped with gimbal-mounted ultra HD video cameras, which can take high resolution photographs and videos of towers and their components for the detection of faults or defects. Patrolling of towers using UAVs will help PGCIL eliminate the need for tower-top patrolling (by climbing the tower) for such inspections. Meanwhile, India’s private utility SPTL, in October 2016, approached the DGCA for obtaining a licence to operate drones for providing transmission line O&M services in the country. Once it gets the permission, or when the country issues general guidelines on operating drones, SPTL plans to offer drone-based O&M services to other transmission utilities besides employing them on its own networks. To obtain the technology, earlier in August 2016, SPTL acquired a minority stake in Finland-based company Sharper Shape to introduce its automated drone-based asset inspection and maintenance services to the Indian transmission sector.

 

From the perspective of utilities, the advantages of using drones in operations are that they are a cost effective, efficient and safe method of carrying out functions that helicopters do for them. Besides being a cheaper and safe option, UAVs can stay airborne for extended periods, use less fuel, have better maneuverability due to their small size, produce less noise and have a lower environmental impact. On the flip side, the privacy issues related to drones are yet to be resolved, which makes it difficult to get licences from the authorities. The line-of-sight restrictions followed by several countries makes it difficult for utilities to fly drones over transmission networks in areas with tall trees and difficult terrain.

 

The use of drones by transmission utilities is still in the nascent stages and the business model they choose will evolve over time. Once its application becomes more established and with greater clarity on the regulations governing UAVs, some utilities may prefer to own small drones for use on their networks and lease them to others (like SPTL in India), while others may lease them from drone companies that already have the necessary licences and permissions.

 

Conclusion

Aerial technologies and methods for inspection and maintenance of transmission lines and project execution are evolving continuously to increase efficiency, provide greater public and employee safety, reduce costs and manpower requirements as well as to extend asset life. While use of aerial technologies by transmission utilities is not a new phenomenon, UAVs are the latest innovation. With greater regulatory clarity and results of the tests and pilots being conducted by various utilities across the world, this technology is expected to become mature and its use more widespread in the coming years.