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Most critical failures in substations don't happen unexpectedly. They develop over time, from signs that can be identified and addressed before they become a problem. What's lacking, in most cases, is a structured routine of inspection and preventive maintenance that transforms these signs into action before the equipment stops working.
This guide brings together the main preventive maintenance routines for substations, the components that deserve more attention, and the best practices that make a real difference in reliability, safety, and operating costs over time.
Why preventive maintenance is cheaper than corrective maintenance.
The logic is simple: halting production at an industrial plant for hours or days due to a transformer or circuit breaker failure costs far more than any periodic inspection program. But the cost goes beyond operational downtime.
An untreated fault has the potential to propagate to other equipment in the substation, transforming a localized problem into a larger-scale event. A transformer with degraded insulation that collapses can damage busbars, circuit breakers, and other components in the same event. The cost of replacing multiple pieces of equipment, added to the downtime and power outages, makes preventive maintenance seem very cheap in comparison.
There is also the safety factor. Poorly maintained equipment poses a real risk to the teams that operate and maintain the facilities. Electrical arcs, fires, and explosions caused by preventable failures have consequences that go far beyond the financial aspect.
Transformers: the component that requires the most attention.
The transformer is the most critical piece of equipment in a substation and, generally, the one with the highest replacement cost. An effective preventive maintenance routine needs to include:
- Analysis of insulating oil: Oil quality is one of the main indicators of the transformer's internal conditions. Physicochemical analysis and DGA (Dissolved Gas Analysis) help identify insulation degradation, the presence of moisture, and signs of internal heating even before any changes are externally noticeable. This preventive monitoring helps anticipate maintenance, reduce operational risks, and increase equipment reliability over time.
- Inspection of terminals and bushings: Check the integrity of the bushings, the absence of cracks, oil stains, and contact resistance at the terminals. Terminals with loose or rusted connections are a frequent source of overheating.
- Temperature monitoring: Check the operation of thermometers and thermostats, and compare the readings with the equipment's nominal parameters. Chronically high temperatures drastically shorten the lifespan of the insulation.
- Checking the oil level and quality: Inspect the level indicator, check seals and gaskets for leaks, and, when necessary, top up or replace the oil according to the manufacturer's specifications.
- Visual inspection of the tank and accessories: Corrosion, deteriorated paint, dried-out seals, and loose screws are signs that need attention before they become a bigger problem.
Circuit breakers and switches: protecting those who protect the network.
Circuit breakers are responsible for interrupting short-circuit currents and isolating sections of the network in fault situations. A circuit breaker that fails to trip when needed can transform a controlled fault into a destructive event. Therefore, its maintenance cannot be neglected.
The main checks include opening and closing time tests, inspection of internal contacts for wear and carbonization, verification of the actuation mechanism, lubrication of moving parts, and testing of the overcurrent trip system. For oil or SF6 circuit breakers, analysis of the insulating medium is also part of the routine.
Busbars and connections: where the heat sounds the alarm
Poorly connected busbars or those with oxidation at the joints generate additional resistance to current flow, which manifests as localized heating. Infrared thermography is the most efficient tool for identifying these hot spots without needing to shut down the installation.
In addition to thermography, periodic visual inspection should check for signs of electric arcing, heating marks on busbar insulation, and the mechanical integrity of bolted connections. The correct tightening torque of the connections should be checked periodically, as vibrations and thermal cycles tend to loosen the joints over time.
Insulators: small components, big responsibility.
Insulators support and electrically separate energized conductors from grounded structures. When an insulator fails, the result can be a serious short circuit. Visual inspection should identify cracks, chips, conductive dirt deposits, and signs of partial discharge, which manifest as charred tracks or arc marks on the surface.
In areas with high pollution, the presence of sea salt, or deposits of conductive particles, regular cleaning of insulators is an essential part of the maintenance routine. The frequency should be determined based on the environmental conditions of the site.
Grounding: the foundation of safety that cannot fail.
The grounding system is the final line of defense against electric shocks and damage from lightning strikes. Its effectiveness depends on grounding resistance within the limits established by standards and on sound connections throughout the entire grid.
Periodic measurement of grounding resistance should be part of the maintenance plan for any substation. Values outside the limits indicate degradation of the buried electrodes, corrosion in the connections, or changes in soil characteristics. Visual inspection of accessible connections, including checking for corrosion and mechanical tightness, should be performed concurrently.
How to structure an efficient preventive maintenance plan
An effective preventive maintenance plan needs three basic elements: defined frequency, clear responsibilities, and systematic recording of inspections and interventions. Without these elements, preventive maintenance becomes reactive maintenance under a different name.
Recommended frequencies vary depending on the type of equipment, the criticality of the installation, and the environmental conditions of the site. In general:
- Routine visual inspections: Monthly or bimonthly inspections focused on identifying external signs of degradation, leaks, dirt, and changes in equipment behavior.
- Infrared thermography: semi-annually or annually, with the substation under normal operating load so that hot spots can be identified.
- Analysis of insulating oil: Annual inspection for transformers in normal operation, with higher frequency for equipment with a history of overloads or anomalies.
- Testing of circuit breakers and protective relays: every two or three years, according to the manufacturer's recommendations and the dealership's requirements.
- Grounding measurement: annually, preferably during the dry season, when soil resistance reaches its highest value.
Identifying impending failures: the signs that cannot be ignored.
Some signs during routine inspections indicate that a fault is developing and require immediate action:
- Unusual noises in transformers, such as intense vibration, crackling, or hissing, may indicate problems in the magnetic core or coils.
- The smell of burnt oil or heated plastic indicates internal overheating that may be close to a meltdown.
- Temperature differences between phases identified by thermography indicate load imbalance or problems in specific connections.
- A progressive increase in grounding resistance measured over time indicates advanced corrosion of the buried electrodes.
- Repeated activations of protective relays without apparent cause may indicate deterioration of insulation or intermittent faults that have not yet become permanent.
Conclusion
Maintaining a substation in good operating condition is not a cost. It is an investment with measurable returns in reliability, safety, and reduced operating costs over time. A well-structured preventive maintenance plan protects assets, teams, and business continuity.
Romagnole has been manufacturing metal cabinets and skids for substations for decades and has in-depth knowledge of the life cycle of this equipment.
If your company is planning a new facility, expanding its electrical infrastructure, or seeking greater reliability for its current operation, the Romagnole team is ready to help you find the most suitable solution for your project.
Contact our sales team and learn about Romagnole's solutions for substations and electrical infrastructure.