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What to do when a large transformer fails
When a large transformer fails, the first decisions shape how long service stays down. This guide covers the practical steps in the first days and weeks, from assessing the damage to finding a replacement.
Why a failure is hard to recover from
According to Wood Mackenzie's Q2 2025 survey, as reported by POWER Magazine, average lead times reached 128 weeks for power transformers. A new replacement ordered after a failure will not arrive for a long time, so the response has to combine temporary measures with a search for an existing unit.
1. Assess the damage
Before deciding on replacement, find out what failed. A bushing or tap changer failure may be repairable on site. Internal winding damage usually is not. Useful information includes protection relay records, a fresh DGA sample, and field tests such as winding resistance and SFRA. Keep records for insurance and for the root-cause analysis.
2. Restore service
Options for restoring service include transferring load to nearby substations, installing a mobile transformer or mobile substation, or borrowing a spare from another utility through a mutual assistance arrangement. These buy time while a permanent solution is found.
3. Write down the replacement spec
Pull the nameplate data, drawings and test reports for the failed unit. The replacement needs to match closely enough to fit the existing installation: MVA rating, voltages and taps, impedance, vector group, BIL, footprint, bushing positions and control connections. Decide early which of these can flex. A search with some tolerance finds more options.
4. Search widely and in parallel
Look at every source at once: utility spares, surplus and never-energized units, released factory slots, and manufacturers with shorter queues. Check transport at the same time. The U.S. Department of Energy estimated in 2014 that transport and logistics account for roughly 3% to 20% of the total cost of a large power transformer, and a heavy-haul route can take weeks to permit.
5. Verify before you buy
Pressure to move quickly is exactly when fraud and mistakes happen. Confirm ownership, nameplate data, test history and storage records before paying. Our used transformer checklist covers what to collect. Use escrow or a letter of credit, not a wired deposit.
6. Afterwards
Once service is restored, review which other substations would be hard to recover and whether spares should be bought or identified in advance. We help with that review for utilities and other owners.
If you have a failure now, start a search.
Sources
FAQ
Common questions
What should we do first after a transformer fails?
Make the site safe, document the failure and gather the failed unit's nameplate and test records. Those records drive the search for a replacement.
Should we repair or replace a failed unit?
That depends on the damage and on how long each option takes. We can look for replacements while your engineers assess the repair.
Can temporary equipment restore service while we wait?
Often. Mobile transformers and substations can bridge the gap, and we look for them at the start of an emergency search.
Tell us what you need.
A 15-minute call is usually enough to scope a search.
Contact details coming soon