The reliable operation of substations and switchgear is critical to ensuring uninterrupted power supply, system stability and network safety. As power systems become more complex and utilities increasingly focus on improving operational efficiency, the role of effective operations and maintenance (O&M) practices has become more important than ever. A combination of planned maintenance strategies, advanced monitoring systems, modern substation technologies and automation solutions is being adopted to improve equipment reliability, minimise outages and optimise asset performance.
O&M practices
Unwanted and unplanned outages due to faults in power systems or equipment failures are among the key concerns for utilities in ensuring reliable, quality power supply round the clock. To maintain system health and reliability, utilities are required to prepare proper maintenance schedules for equipment across the power sector. Broadly, equipment maintenance may be categorised as planned or unplanned.
Utilities undertake various maintenance practices, including preventive maintenance, predictive maintenance and reactive/breakdown maintenance. Reactive maintenance is unplanned in nature and is carried out after a fault or equipment failure has occurred. In contrast, planned maintenance practices are proactive and are designed to prevent failures and improve equipment performance. These include preventive maintenance, which is undertaken at predetermined intervals, and predictive or condition-based maintenance, which relies on monitoring equipment condition to identify potential issues before failures occur.
Preventive maintenance
Preventive maintenance in substations and switchgear systems refers to planned and pre-emptive maintenance activities undertaken to ensure efficient operation of electrical infrastructure. It involves systematic inspection, detection and rectification of potential issues before they lead to equipment failure or major damage. Preventive maintenance is critical for maintaining the reliability, availability and operational performance of key assets such as transformers, circuit breakers, isolators, relays and associated switchgear equipment.
Preventive maintenance, also referred to as scheduled maintenance, is carried out at regular intervals based on two key approaches – time-directed O&M and useful life-based maintenance. Time-directed maintenance is undertaken according to the number of operations, operating hours or seasonal requirements, while useful life-based maintenance is performed when equipment condition approaches operational limits to avoid incipient failures.
Common preventive maintenance practices in substations and switchgear systems include regular inspection of equipment to identify abnormalities at an early stage, cleaning and lubrication to minimise corrosion and wear, and periodic testing of insulation systems, electrical connections and equipment performance. Utilities also replace worn-out or obsolete components such as breakers, switches and fuses to maintain operational reliability.
An effective preventive maintenance programme must be customised to meet utility-specific requirements and implemented in a cost-effective manner. At the same time, maintenance schedules must be carefully planned to minimise consumer interruptions while extending equipment life and improving replacement planning.
Predictive maintenance/condition monitoring
Unlike routine maintenance schedules, predictive maintenance is based on the actual condition of equipment and is carried out as and when necessary before failure occurs. Maintenance schedules are prepared using condition monitoring data collected periodically to analyse equipment performance, identify condition trends, compare historical data and undertake diagnostic assessments.
In substations and switchgear systems, condition-based maintenance helps identify abnormalities in critical equipment before they develop into system-critical failures. This enables utilities to undertake maintenance activities in a planned manner, thereby improving equipment uptime, reducing maintenance costs and optimising spare inventory. Increasingly, predictive maintenance is being supported through IT-based condition monitoring systems installed across substations and field equipment.
Condition monitoring systems use sensors to provide insights into the health of equipment and monitor operating parameters such as transformer temperature, oil level and overloading conditions in transformers and associated systems. The data collected through these systems can be analysed to support predictive maintenance planning for critical substation and switchgear assets. Advanced analytics and artificial intelligence-based assessment of sensor data are also being explored to anticipate equipment failure and identify maintenance requirements in advance.
Utilities may initiate predictive maintenance based on reports generated by detectors and sensors such as thermovision cameras and partial discharge detectors to identify hotspots and discharge activity. Thermography equipment and portable non-contact temperature measurement devices can also be used to detect hotspots in transformers, connectors, joints and feeder pillars. In addition, periodic transformer oil testing helps assess equipment health and enables corrective actions to prevent failures.
Reactive/breakdown maintenance
Reactive maintenance, also known as breakdown or repair maintenance, is carried out after the failure or damage of equipment such as circuit breakers, transformers, isolators, relays, busbars, switchgear panels and associated systems. Equipment failure, except in cases of natural calamities or force majeure conditions, is largely attributed to poor maintenance practices, delays in inspection and servicing, overloading and failure to respond to condition monitoring indications. Such failures can lead to outages, operational disruptions, safety risks and financial losses for utilities. Reactive maintenance in substations and switchgear systems can be minimised through the timely adoption of regular preventive and predictive maintenance practices, ensuring reliable equipment performance and improved system availability.
GIS maintenance
Gas-insulated substations (GIS) are increasingly preferred owing to their high reliability, compactness and suitability for challenging operating environments. Compared to conventional air-insulated substations, GIS requires significantly lower land area, generally in the range of 10-20 per cent for switchgear bays, making it particularly suitable for urban and space-constrained locations. GIS installations are also advantageous in areas exposed to saline pollution, industrial contamination, extreme temperatures, high altitudes and seismic conditions, where enclosed equipment design provides greater immunity to environmental stresses.
From an O&M perspective, GIS maintenance requires strict adherence to manufacturer-recommended safety procedures and maintenance schedules. Maintenance activities are generally based on prescribed time intervals or the number of operations, whichever occurs earlier. Prior to carrying out any maintenance, utilities must ensure that only authorised personnel are deployed, maintenance activities and associated hazards are clearly defined, and proper maintenance records are prepared. Further, only original equipment manufacturer-approved parts should be used during maintenance activities.
A key requirement in GIS maintenance is the proper isolation of equipment. The identified equipment must be de-energised and de-gassed, with adequate earthing provided on all sides of the work zone. The work area should be barricaded and maintenance personnel equipped with appropriate protective clothing and safety devices. Maintenance tools, platforms, slings and electrical equipment must also be checked for operational readiness.
Further, condition monitoring forms an essential component of GIS O&M. Since SF6 gas is used across GIS chambers, the regular monitoring of gas pressure, quality and dew point is critical for maintaining insulation performance. Leakage rates, pressure variations and gas quality are closely monitored to ensure reliable and safe substation and switchgear operation.
Automating O&M
Substation automation has become an important component of O&M of substations and switchgear, enabling improved monitoring, control and operational efficiency. An open systems approach is particularly significant in substation automation as it supports supplier-independent standards, allowing software and hardware from different vendors to interoperate effectively. For substations and switchgear, this ensures that intelligent electronic devices (IEDs), protection systems and control applications can exchange information seamlessly without dependence on proprietary technologies. Such systems provide longer operational life, investment protection, upgradeability and expandability, while also enabling the integration of readily available third-party components at lower cost and risk.
In the O&M of substations and switchgear, automation can be understood across multiple levels of integration. At the base level are primary substation assets such as power transformers, circuit breakers and switchgear equipment. The next levels involve the implementation and integration of IEDs, including digital relays, multifunction meters and controllers capable of sending and receiving operational data and control signals. Utilities are increasingly focusing on integrating these IEDs to improve coordination between protection, monitoring and control systems within substations.
Substation integration supports O&M by combining protection, control and data acquisition functions into a minimal number of platforms, thereby reducing redundant equipment, panel space and operational costs. At a higher level, substation automation deploys functions such as supervisory control and data acquisition, alarm processing and feeder operation management to optimise asset utilisation and improve maintenance efficiency with minimal human intervention. This enables utilities to enhance the reliability and operational effectiveness of substations and switchgear systems.
Conclusion
As utilities strive to ensure reliable and high-quality power supply, effective O&M of substations and switchgear has emerged as a key priority. Preventive, predictive and reactive maintenance practices, along with specialised GIS maintenance and increasing adoption of substation automation, are helping utilities improve equipment reliability, reduce downtime and enhance operational efficiency. Going forward, the greater integration of condition monitoring systems, intelligent devices and automated control platforms is expected to further strengthen asset management and support the safe, efficient and resilient operation of substations and switchgear systems.
