Transformer Maintenance and Testing: A Practical Guide for Nigerian Facilities

A distribution or power transformer is often the most expensive single item in a facility’s electrical system, and when it fails, everything downstream stops. In Nigeria, transformers work hard: high ambient temperatures, humidity, voltage swings from the grid and long periods of heavy loading all speed up ageing. A simple maintenance and testing plan keeps your transformer healthy and warns you early when something is wrong.

Routine checks (weekly to monthly)

These visual checks can be done by trained facility staff from a safe distance, without opening anything:

• Oil leaks: look for oil on the tank, radiators, valves and the ground below.
• Oil level: read the conservator oil level gauge.
• Temperature: record oil and winding temperature readings and note any rise over time.
• Silica gel breather: check the colour of the silica gel. Once most of it has changed colour, it is saturated and needs replacing, or moist air will reach the oil.
• Noise and smell: unusual humming, buzzing or a burning smell need investigating.
• Surroundings: keep the transformer area fenced, clear of vegetation and free of stored items.

Quarterly checks

• Thermal imaging of HV and LV terminations and cable boxes to find hot connections
• Check cooling fans and radiators, where fitted
• Check bushings for cracks, dirt and tracking marks
• Inspect the earth connections to the tank and neutral
• Check protection indications such as Buchholz relay and temperature alarms

Yearly testing

Annual tests should be carried out by qualified engineers with the transformer safely isolated and earthed:

• Insulation resistance (IR) and polarisation index (PI): shows the condition of winding insulation.
• Transformer oil testing: dielectric strength (breakdown voltage) and moisture content. Dissolved gas analysis (DGA) gives early warning of internal faults in larger units.
• Turns ratio (TTR): confirms the windings and tap changer are healthy.
• Winding resistance: finds loose internal connections and tap changer contact problems.
• Earth resistance: confirms the neutral and tank earths are effective.
• Protection checks: Buchholz, temperature trips and the upstream breaker or fuse protection.

Keep every year’s results. The trend matters as much as the individual reading: a steady fall in insulation resistance is an early warning, even if each reading still looks acceptable.

Oil treatment

When tests show high moisture or low breakdown voltage, the oil can often be filtered and dried on site rather than replaced. Badly degraded oil may need to be replaced. Either way, find and fix the cause, such as a saturated breather or a leaking gasket.

After a fault: return-to-service assessment

If a transformer has tripped on a fault, been flooded, or been out of service for a long time, do not simply switch it back on. A return-to-service assessment, including IR, TTR, winding resistance and oil tests, tells you whether it is safe to energise. Energising a damaged transformer can turn a repairable fault into a total loss.

Signs your transformer needs attention now

• Oil leaking or a falling oil level
• Rising operating temperature at similar load
• Silica gel fully discoloured
• New noise, smell or visible arcing marks
• Repeated protection trips

Talk to Corustar

Corustar Technological Services is an electrical engineering contractor based in Ikeja, Lagos, working across Nigeria. See our Transformer Services service, request a quote, or call +234 816 976 9672. For outages and faults, call our 24/7 emergency line on 0705 739 9297.