Asset management is one of the most complex elements of the utility business. For transmission enterprises, it is a core function and is strongly linked with both revenue and reliability of electricity supply. Decisions need to be made on a continuous basis during the lifespan of a transmission line, with emphasis on extending the life of the assets, maintaining or improving reliability and performance, optimising costs and ensuring safe operation of the system. In India, many transmission lines that were built decades ago are beginning to show their age and now approaching the end of their expected lifetime, necessitating asset maintenance and monitoring. Besides, the large influx of renewable energy is causing the network to undergo rapid changes, in the process of moving towards a smarter grid. The management of the existing ageing network along with an evolving grid calls for enhanced asset management by utilities.
A range of different techniques like condition-based monitoring (CBM), time-based condition monitoring (TBCM), time-based maintenance (TBM) and online condition monitoring (OLCM) are followed for maintenance purposes.
CBM comprises condition monitoring, assessment and maintenance actions (including refurbishment and replacement), based on the condition. It has two main functions – first to prevent a functional failure and, second, to mitigate the consequences of that failure. CBM has the potential to increase availability of equipment, reduce the occurrence of major failures, and reduce routine and remedial maintenance costs. For CBM to work, it is necessary to be able to predict the onset of failure early enough to rectify the problem or avoid the consequences of failure. At moderate maintenance costs, CBM leads to high availability of transmission assets. A refined version of CBM is reliability-centred maintenance, whereby the maintenance schedule is optimised by considering two aspects: the condition of the equipment and the importance of the equipment for the network. TBM is planned maintenance, as it must be scheduled in advance. A maintenance plan for a piece of equipment is put together that needs to be performed regularly. With the maintenance plan in place, the maintenance is performed each time the calendar rolls over the specified number of days. This means that it can be used with both predictive maintenance and preventive maintenance.
Tools and technologies
Power Grid Corporation of India Limited (Powergrid) incorporates various advanced technologies to maintain transmission lines. Geographic information system (GIS) mapping is helpful in performing corridor mapping, vulnerability (flood and fire) analysis, mapping the change in the course of rivers and hence, in disaster-preparedness. It involves the mapping of transmission towers with the help of GPS coordinates, which are mapped to either Google or the Bhuvan platform. Aerial patrolling of lines using helicopters and tower-top patrolling using drones has also begun in India in areas such as deep forests, hilly terrainand snow-bound areas, where ground patrolling is difficult and time-consuming. These helicopters are also equipped with gimbal-mounted LiDAR (light detection and ranging), thermovision cameras, and high resolution video and digital cameras to identify defects in transmission lines. They eliminate the need for tower-top climbing for detailed inspection. Powergrid also uses an Android-based application, Patrosoft, to generate reports and alerts.
Besides, for transmission lines of up to 765 kV, hotline maintenance is done using insulated buckets. In order to avoid pollution, room temperature-vulcanised coating is used on all insulators in a 50 km range of the coast. A process bus uses optical fibre to avoid fire in the cables. In the case of copper cables, this technique helps in preventing widespread damage to transformers due to fire. Another advantage of a process bus is that it reduces the number of cables and earth faults in the direct current system, while also being economical
At the substation level, Powergrid is integrating online monitoring systems with its National Transmission Asset Management Centre, regional transmission asset management centres and local supervisory control and data acquisition system. It also uses resin impregnated paper bushings, which are explosion-proof and fire-resistant and help in avoiding breaking of the porcelain insulator inside the transformer. Controlled switching is another method used to avoid reignitions and to minimise inrush or magnetising currents. The method of dynamic contact resistance measurement has helped in drastically reducing the number of failures of extra high voltage circuit breakers. It helps in judging the health of arcing contact in addition to the main contact.
In essence, asset management plays an important role in avoiding abnormal stress in the transmission system and in obtaining the data needed for planning suitable maintenance (or replacement) measures before the occurrence of a failure. Technology advancement is enabling more efficient implementation of asset management, leading to an increase in system availability. In the future, efforts would be required to cover all the assets across the country, and to analyse data more effectively for enhanced asset management and operation.