Transformers play a critical role in ensuring secure power supply. Their health and reliability are essential for ensuring seamless electricity transmission and distribution. With the growing power transmission network, operations and maintenance (O&M) of transformers is a strategic and priority area for power utilities. Transformer failures have far-reaching consequences. There can be various reasons for such failures, including the age of the transformer, and leakages leading to accelerated ageing of insulation material or insulation failure. Therefore, effective O&M of transformers is imperative to ensure optimal functioning of assets, extend lifespans, reduce repair costs, maximise performance and minimise downtime.
Power Line takes a look at some of the most widely used O&M practices…
Standarisation of operational practices
There are notable variations in the operational practices of utilities, particularly between private and government-owned utilities. While private utilities have generally adopted more advanced practices, there is potential for further improvement, across both public and private utilities. A key strategy is the integration of transformer metering with smart metering capabilities in order to monitor and address issues such as overvoltage, overloading and unbalancing. Additionally, the probability of equipment failure can be reduced by minimising the use of tap changers. Protective measures such as applying an anti-corrosion coating or paint to the transformer’s outer tank are effective in guarding against rust and deterioration. Operational efficiency can also be improved by using fuses with high rupturing capacity or horn gap fuse systems, and introducing lug or clamp connections between risers and bushings to help avoid internal open-circuit faults.
Analysis of cause of failure
Since the causes of transformer failures are very diverse, thorough failure analysis is needed to identify the root cause and implement the best corrective solution. A transformer’s longevity is closely related to the health of its insulation system, which degrades over time, especially under temperature stress. Heat generated from internal losses accelerates insulation ageing, producing gases that can be detected through dissolved gas analysis. This is a diagnostic tool for transformers that can help identify the type and degree of abnormality, as well as the urgency of corrective action. Apart from this, factors such as harsh operating environments, exposure to extreme weather, overloading, poor line protection and substandard maintenance practices can significantly elevate the risk of transformer failure. These factors can be more commonly found in rural areas. Additionally, rural transformers often face unbalanced loads, unauthorised tapping and low efficiency. Moisture ingress, a common issue in such regions, further weakens insulation by causing sludge accumulation and hindering oil flow. The lack of upkeep of feeder lines and protective devices adds to the operational challenges, increasing vulnerability to breakdowns.
Inspection
To ensure the longevity of transformers and prevent equipment failure, regular asset inspections are crucial. These inspections also help in reducing the need for emergency maintenance, which is generally costly. For this reason, visual inspection for signs of physical damages, such as cracks, liquid leaks, corrosion, damaged connectors, burning odours or loose plugs, is a critical component of any O&M strategy. Further, in order to prevent insulation breakdown and reduction in lifespan from overheating, it is essential to monitor the temperature of assets. Additionally, undertaking electrical testing of transformers by checking for proper grounding and insulation resistance is necessary to ensure the correct functioning of these assets. The Central Electricity Authority’s (CEA’s) guidelines for the O&M of distribution transformers states that utilities that undertake these maintenance activities are able to minimise their transformer failure rate to less than 2 per cent. Besides this, widespread deployment of advanced technologies, such as computerised maintenance management systems, must also be encouraged to help utilities automate the process of recording and tracking all maintenance activities, thus improving the efficiency and effectiveness of these inspections.
Preventive maintenance
Preventive maintenance of transformers encompasses a wide set of activities, including cleaning of insulation and the tank by vacuuming, wiping down surfaces and applying lubricant to moving parts. To gauge the condition of insulation materials inside the transformer, regular oil analysis should be carried out. This is done by performing tests to analyse the oil’s breakdown voltage, dielectric strength, moisture content and acidity levels. By carrying out these tests, issues such as contamination or degradation of oil can be detected at an early stage, and measures to prevent further damage to the transformer can be deployed. In addition to this, the breather unit, containing silica gel and an oil seal, should also be routinely inspected to ensure optimal functioning. Further, proper periodic examination of electrical connections at both high and low voltage terminals is essential for checking tightness, integrity and cleanliness. Any tension or strain caused by unsupported cables or conductors should be promptly addressed. Furthermore, inspection of cooling systems, bushings and other external components should be carried out for detection of surface contamination.
Over the lifespan of a transformer, reconditioning is recommended every 15-20 years. This process typically retains the magnetic core, while improving performance through measures such as winding redesign and material upgrades, such as switching from aluminium to copper windings. This process is beneficial in reducing technical losses, enhancing the kVA rating and improving the overall reliability of the transformer.
Monitoring via IoT
Although maintenance and monitoring of transformers are crucial, manual monitoring is highly unfeasible due to its time-consuming and labour-intensive nature, making it a costly activity. As a result, IoT-based technologies are increasingly being adopted by utilities for real-time monitoring of transformer condition. By leveraging machine learning algorithms, IoT sensors help in keeping track of parameters such as moisture levels in the oil, along with monitoring of leakages, power factor, voltage, bushing and winding. Additionally, IoT-based distribution transformer monitoring units help in transmitting monitoring data to the control centre via communication technology in real time. This allows utilities to detect potential failures and address these problems before they escalate.
Furthermore, in urban areas, a large number of transformers are now integrated with communicable meters that support automatic meter reading (AMR), enabling remote meter reading at data centres and enhancing energy accounting and auditing processes.
Challenges
There are quite a few challenges on the road to optimal transformer maintenance. First, inconsistencies in manufacturing processes and material quality, largely due to frequent changes in suppliers, sub-vendors and skilled manpower, often result in differences in transformer quality and reliability. Moreover, manufacturing of transformers in environments lacking dust control or humidity regulation can lead to assets with suboptimal quality and a reduced lifespan. Setbacks are also often caused due to limited on-site testing options, along with improper handling during transportation, storage, erection and commissioning. Additionally, poor practices, such as neglecting preventive maintenance, improper earthing, overloading and the use of substandard materials, further weaken transformer health. Security issues, such as tampering with protection systems or theft of oil and components, also pose risks of fire and catastrophic failures. Ironically, while technology has helped reduce the monitoring burden, issues associated with AMR systems, misalignment or malfunctioning of modems, communication breakdowns, and lapses on the part of utility staff in reconnecting metering systems after transformer replacements are not uncommon.
Conclusion
Going forward, utilities must increasingly prioritise O&M strategies to keep up with the rapidly expanding transmission and distribution networks. These strategies are necessary for boosting the operational efficiency of transformers by way of early fault detection and mitigation of failures. Wider adoption of advanced remote monitoring technologies would further enhance transformer health and performance. Ultimately, an increased focus on proactive maintenance and technological integration will be fundamental in ensuring transformer reliability and sustainability of the power system in the long term.