Asset management involves a strategic and systematic approach to managing physical assets, with a focus on business and engineering processes for resource allocation and utilisation. This enables better decision-making based on quality information and well-defined objectives.
The end goal of using asset management strategies is to optimise costs, reduce risks and improve performance. In the transmission segment, advanced hardware and software asset management strategies such as aerial patrolling, hotline maintenance, transmission line arresters and advanced software for real-time tracking of equipment performance can increase situational awareness as well as significantly reduce maintenance costs. A look at the latest trends in transmission technologies, and the operations and maintenance (O&M) solutions being deployed in the segment…
Latest technologies in transmission
Given the land constraints, the adoption of new designs that economise space has been a key trend in the transmission segment. For instance, high temperature low sag (HTLS) conductors are being deployed. These conductors have high power transfer capacity and also enhance the thermal limit of the existing lines.
Structural optimisation is being incorporated by using narrow base, multicircuit towers in place of conventional towers. This reduces the right-of-way (RoW) requirements. Similarly, GIS substations are being deployed to reduce the overall substation area and also to bring down maintenance needs. At present, the country’s largest power transco, Power Grid Corporation of India Limited (Powergrid), operates a total of 54 GIS stations. Also, hybrid substations are being set up by utilities to optimise space.
Further, process bus technologies, where the connection from equipment to control room is through fibre optic cable, are being adopted to cut down the number of copper wirings required and the downtime. This increases reliability and eases troubleshooting. Digital substations based on process bus technologies have been planned by Powergrid.
The use of resin impregnated paper (RIP) bushings is gaining traction over oil impregnated paper bushings. RIP bushings are explosion-proof, and fire-resistant and can save the porcelain insulator inside the transformer from breaking. Powergrid started using RIP bushings up to the 400 kV level in various transformers and reactors in 2014. It is now planning to procure RIP bushings of 765 kV on a trial basis.
Ester oil as an insulating medium is also being adopted for transformers. It is beneficial, as it is safe and has a fire point over 300 degrees Celsius. Moreover, it is completely biodegradable, and is non-hazardous to water, and also increases the lifespan of the transformer due to its slower degree of polymerisation and a higher capacity to absorb moisture. Powergrid has procured one transformer with synthetic ester as the insulating medium while another reactor is being procured with natural ester as the insulating medium.
O&M practices and solutions
Powergrid is deploying assets at a compound annual growth rate of 15 per cent. These assets increased from 231,709 MVA during 2014-15 to 368,512 MVA during 2018-19. Thus, the company is making efforts to improve their operational performance. From usage-based and condition-based maintenance, Powergrid has moved to predictive and reliability-centred maintenance of its assets.
Transmission lines and towers
Aerial patrolling of lines using helicopters and drones, as well as ground patrolling are some of the methods being used for monitoring transmission lines and towers. On a single day, aerial patrolling of 100-150 km can be done using helicopters to detect defects like broken insulators and hot spots. Helicopters are equipped with gimbal-mounted LiDAR (light detection and ranging), thermovision cameras, and high resolution (HD) video and digital cameras to identify defects in transmission lines. They eliminate the need for tower-top climbing for detailed inspection. Meanwhile, drone patrolling provides detailed information about the tower-top portion, that is, the condition of insulators, earth peak, earth wire, etc. Drones are equipped with gimbal-mounted ultra HD video cameras that can take high resolution photographs and videos of towers, especially the top portion components.
Ground patrolling gives detailed information about the lower portion of towers, that is, the condition of the foundation, earthing, bracing, tower components, etc. For improving ground patrolling, an Android-based application, Patrosoft, is being used for checking patrolling progress and updating patrolling data.
Powergrid has indigenously mapped its towers on the geographic information system (GIS). This is helpful in performing corridor mapping, vulnerability (flood and fire) analysis, mapping the change in the course of rivers and hence in disaster preparedness. This is done using GPS coordinates, which are mapped to either Google or the Bhuvan platform. Recently, during the cyclones that impacted the states of Odisha and Gujarat, the GIS platform was used to identify the transmission lines that came in the path of these cyclones and this helped in taking adequate measures.
Another initiative is hotline maintenance using insulated bucket trucks. This helps in early defect rectification, outage management, enhancing the availability as well as hotline maintenance till the 765 kV voltage level. The adoption of transmission line arresters (TLAs) in lightning-prone areas has helped in reducing trippings..
For the operation and maintenance of substations, condition monitoring tests are carried out for all equipment (like transformers and reactors, circuit breakers, CVTs and surge arresters) on a periodic basis. For instance, through dynamic contact resistance measurement of EHV circuit breakers, the number of failures can be drastically reduced as it can help in determining the health of arcing contact in addition to the main contact.
Frequency domain spectroscopy is another method for testing bushings. The tan delta of bushings is normally measured at 50 Hz. However, in some cases bushings fail even when they have normal tan delta values of 50 Hz. Thus, tan delta measurement of bushings across a frequency range of 1 MHz-1 kHz can be carried out for accurate results.
Controlled switching of transformers and reactors is another method which can be used to avoid reignitions and minimise inrush or magnetising currents. This can also reduce the stress on electrical devices, since fewer transients develop during circuit breaker switching.
Another O&M initiative undertaken by Powergrid is asset health indexing (AHI). Given its large base of transformers and reactors (about 2,300), manual monitoring of test results of such a huge fleet of equipment is difficult. AHI software has been developed indigenously to monitor the test results of transformers and reactors at a glance. This has enabled automatic analysis of equipment health, and helped in leveraging existing infrastructure and data.
The regular upgradation of assets to meet latest operational requirements is another key O&M strategy. This includes the replacement of static relays with numerical relays, the replacement of protection and control schemes of old substations as well as transformers with higher rating units to meet increased load demand around substations. Also, ageing assets can result in high O&M expenses and failures might lead to long outages. Thus, based on residual life assessment studies, further action for replacement can be taken.
Many challenges can emerge while undertaking O&M practices. For instance, RoW issues come up during line maintenance. Powergrid had to face severe agitations from local residents during line maintenance activities. Such situations require support from local administration and the local residents.
Further, adverse climatic conditions such as change in wind zone and cyclones pose a threat to transmission towers. Also, smog and insulator contamination due to industrial activities can cause insulator flashovers. These bottlenecks can be addressed through upgradations to tower designs. Emergency restoration system towers can be used for the early restoration of damaged transmission towers. The replacement of insulators with polymer/RTV-coated glass insulators is being carried out in high pollution areas.
An emerging challenge, is related to cybersecurity of the transmission network. To address this, a security incident and events monitoring system has been deployed at the centralised National Transmission Asset Management Centre. An information security lab has also been set up at Manesar. Going forward, gap assessment in cybersecurity of SAS systems is planned to be done by end 2019. Data link authentication from substations to RLDCs is planned to be done by 2021. Also, a centralised security operations centre is planned to be set up by 2023.
In sum, over the next few years, as the transmission network expands to integrate the rapidly increasing renewable energy capacity and adopts new and disruptive technologies, it will be critical for utilities to focus on asset management practices to effectively monitor and control these assets.
Based on a presentation by Seema Gupta, Director, Operations, Powergrid, at a recent Power Line conference