Amid rapid evolution in the power landscape, transmission companies need to optimise the performance of their existing assets for cost-effectively achieving numerous operational goals. Asset management is the backbone of utilities in the power sector and helps to enhance an asset’s useful life. Asset management strategies focus primarily on condition assessment, refurbishment, replacement of assets, maintenance management and the adoption of technologies for extending asset life. Transmission companies today are evolving their asset maintenance approach and adopting new asset management strategies. In order to ensure a perpetual improvement in the maintenance of assets, various approaches ranging from run to failure to financial optimisation play a key role.
Asset maintenance strategies
Run to failure
Run to failure, also known as reactive maintenance or breakdown repair, is needed when equipment is redundant and can be replaced immediately. Upon exercising proper implementation, the run-to-failure approach eliminates the risk of over-servicing basic equipment, ensuring that it is only being used on non-critical components with minimal or no effect on health, safety or operation.
Time-based maintenance is based on original equipment manufacturers’ schedules or used for regulatory compliance. This may include servicing of fans, pumps, firefighting systems, and diesel engine sets. Once the equipment is installed, a maintenance regimen associated with it needs to be adopted. This comes along with a risk of over-servicing or under-servicing, depending on the time interval of maintenance. The maintenance intervals in time-based maintenance are usually shorter than required. However, for critical equipment, time-based maintenance can be an inefficient approach to follow.
Usage-based maintenance is based on the usage of equipment, that is, overhauling of breakers after certain operations and so on. Usage maintenance based on operational data is a lucrative approach, and for many assets, equipment use is a more reliable predictor of failure than time. This approach is generally combined with a time-based maintenance approach, and maintenance takes place where any of the two criteria are met.
Condition-based maintenance involves maintenance based on the actual condition of equipment. This approach is ideal in cases where a measurable parameter capable of being a good indicator for impending problems exists. Although the approach is not cheap, it can considerably bring down the high costs incurred in excessive time-based maintenance.
Usually done for highly critical equipment, predictive forecasting is another crucial strategic approach. It is rapidly becoming a golden investment opportunity due to an increased understanding of data analytics and predictive modelling among key players. Predictive forecasting is applied to long-lead-time assets, service-interrupting assets, and difficult-to-access assets such as transformers. For instance, frequency domain spectroscopy (FDS) of bushings, dissolved gas analysis (DGA) of transformers, thermovision scanning, and integration of different results in a risk-based health index results in predictive analysis.
Reliability-centred maintenance deals with individual maintenance plans for each asset, depending on their criticality and importance to grid operations. One of the key outcomes of this approach is the failure mode analysis. Once performed correctly, the outcome should be information that can alter the existing maintenance approach, thereby avoiding future failures. For instance, the interval between inspections may be shortened or lengthened, or the threshold for tolerance of a condition reading might be raised or lowered, making reliability-centred maintenance a management tool and a “feedback loop” for other maintenance strategies. It is worth noting that the best candidate for this approach is equipment that is critical for operations, with little or null redundancy, can highly impact operational cost or result in safety or environmental hazard, has an expected long life in terms of operation, is unique or custom-made and, therefore, the operating and maintenance plan may need to be altered over time, and lastly, is likely to impact grid operation in the event of failure.
Transmission lines and towers
Several transmission line and tower maintenance practices, including patrolling, have gained traction over time. At ground level, the use of GPS-enabled apps and high-resolution cameras is beneficial whereas at the aerial level, helicopters, drones and GIS mapping are preferred.
Powergrid’s PG DARPAN (Powergrid Digital Application for Routine Patrolling and Assessment of Network) application has made it easier to geographically map transmission line towers for better asset management. The app helps improve patrolling efficiency with the automatic generation of patrolling plans, real-time monitoring and patrolling summaries.
Helicopter-based aerial patrolling is also playing a key role in efficient asset management, coupled with LiDAR mapping of lines, insulator condition monitoring, hardware condition monitoring, and thermovision scanning. While drone-based patrolling can play a pivotal role in the inspection of damaged insulators and loose jumper bolts, ground patrolling gives detailed information about the lower portion of the tower, that is, condition of the foundation, earthing, bracing, tower members, etc. Another advantage of helicopter-based aerial patrolling is that it specialises in the provision of information regarding electrical clearances, hotspots, etc. and provides detailed information about the tower top portion, that is, details about the condition of insulators, earth peak, earth wire, etc.
Substations and transformers
Condition monitoring tests are a part of major O&M practices for substations. They are carried out by Powergrid for all types of equipment in a substation on an annual basis. Major condition monitoring tests carried out for substation equipment include capacitance and tan delta of bushings, capacitance and tan delta of windings, core insulation test, DGA sampling, frequency response analysis (FRA), and FDS. Further, the National Transmission Asset Management Centre (NTAMC) set up by Powergrid is managing remote operations of nearly 255 substations, across 11 regional transmission asset management centres (RTAMCs).
Powergrid has also developed an in-house web-based portal called PALMS (Powergrid Asset Life Management System) for approximately 3,400 transformers and reactors. Categorising critical equipment based on the operational experience and the latest international standards, the platform offers risk-based indexing of transformers/reactors. In addition to this, a dashboard for monitoring critical equipment exists. With customised report generation and trend analysis of test parameters, automation of manual processes such as DGA review and maintenance planning, a well-developed asset life management system helps in mitigating future equipment failures.
Issues and challenges
To operate and maintain asset management equipment in the best possible way, several bottlenecks need to be tackled. Unforeseen issues such as natural calamities can be detrimental to the health of assets. With changing climatic conditions, cyclonic winds in coastal areas, patrolling in tough terrains, especially in states like Jammu and Kashmir and Arunachal Pradesh, can be difficult. Moreover, ageing asset fleet of substations, breakdown restoration of GIS bays, and cybersecurity for transmission network need to be taken care of on a regular basis.
To address such issues, appropriate strategies must be undertaken, taking care of system availability and other performance parameters. Periodic upgradation of equipment as per requirements should be done to avoid future backlashes. Upon failure, the equipment should be replaced at regular intervals for maintenance purposes. Moreover, the future of reliability-centred maintenance should also be taken care of, addressing concerns ranging from security to financial optimisation.
A number of new and upcoming solutions can also be deployed such as robotics for transmission line maintenance (TLM) and substation maintenance, insulated bucket truck for hotline maintenance, travelling wave fault locator for accurate fault location, process bus module for digital substations, and virtual reality (VR)/augmented reality (AR) kits for training.
New initiatives such as digital substations and reactors with natural ester oils can also help address some of the asset management challenges. For instance, on August 27, 2021, the world’s first 400 kV reactor with natural ester oil was commissioned by Powergrid at the Maithon substation in West Bengal. Derived from renewable agricultural seed crops, application of ester fluids at higher voltage levels provides utilities with a safe and green solution for high equipment performance. It is biodegradable in nature, ensuring minimal environmental footprint, and has higher fire resistance properties as compared to mineral insulating oil. The fire point of natural ester is 360 degrees Celsius while that of mineral oils is 160 degrees Celsius. Also, the flash point of natural ester is 310 degrees Celsius while that of mineral oil is 140 degrees Celsius.
Also, India’s first 400 kV digital substation was commissioned at Malerkotla, Punjab, by Powergrid on December 16, 2020. With this notable development, Powergrid has become one of the very few utilities in the world to retrofit a substation completely with digital technology. In an extra high voltage (EHV) or ultra high voltage (UHV) substation, the technology provides flexibility in engineering, thereby paving the way for quicker commissioning, a reduction in downtime, enhancement of diagnostics and ease in troubleshooting during asset management. This also helps in reducing environmental footprint with the reduction in requirement for copper cables and civil works.
To conclude, efficient asset management strategies are being adopted across the country, taking into consideration the complexities of maintenance management as well as the natural barriers facing the transmission sector. Furthermore, in-depth analysis of management processes, coupled with failure detection and forecasting techniques, can help utilities build a robust asset base for the network.
Based on inputs from a presentation by A.P. Gangadharan, Executive Director, Asset Management, Powergrid, at a Power Line conference