Transformer condition assessment across a fleet
A structured survey of your transformer population that produces a ranked, evidence-based picture of asset health and a prioritised intervention plan.
Who a transformer condition assessment is for
A transformer condition assessment turns a fleet of uncertain condition into evidence: every unit sampled, the units the results single out tested on site, and the whole fleet ranked by condition and risk. It is the usual first step, because it decides where the budget of any later programme goes.
Utility, TSO and DSO asset managers
You decide between repair and replacement inside a multi-year plan and a fixed budget. Whether the plan is regulated or funded by a development bank, each intervention has to be justified with condition evidence, and the assessment produces it unit by unit.
IPP asset owners
Availability obligations, and lenders who expect documented, auditable asset management. The assessment gives test evidence with the method recorded beside each result, in a form a lender's technical adviser can review.
Mine and plant engineering managers
A transformer fleet whose condition nobody has measured, often with gaps in the records. The assessment establishes what you have before money goes to any single unit.
Fleets past their design life
In Europe and the UK many units have outlived their design life and now carry renewable in-feed and reverse power flow they were not specified for. The assessment shows which are fit to stay in service, which need work and which should be replaced.
Owners about to commit capital
Before a unit is refurbished or replaced, the assessment says whether it justifies the spend, so the programme that follows is sized to the fleet you actually have.
What a fleet condition assessment includes
Oil sampling across the whole fleet
Every transformer is sampled, not a selection. Samples for dissolved gas analysis are drawn to IEC 60567, and samples for the other oil tests to IEC 60475.
Oil analysis to published methods
Dissolved gases, breakdown voltage, water content, acidity, dissipation factor, interfacial tension, corrosive sulphur and oxidation inhibitor content, each reported with its method and read against the unit's own earlier results where they exist.
On-site electrical diagnostics on priority units
Winding resistance, turns ratio with vector group and polarity, insulation resistance and polarisation index, tan delta and power factor of windings and bushings, sweep frequency response analysis to IEC 60076-18, excitation current, short-circuit impedance, core insulation and thermography under load.
Bushing condition
Measured capacitance and tan delta are compared with each bushing's nameplate values under IEC 60137. Drift in either can mean water has entered the bushing, or the insulation between its grading layers has started to break down.
Condition scoring and risk ranking
Each unit is scored for condition and risk from its results, its records and its duty, and given an indication of remaining life.
A capital and maintenance plan
The assessment ends in a plan that says which transformers to treat, which to rehabilitate and which to replace, and in what order.
How the assessment runs, from sampling to a plan
Phases, in order. The size of the fleet sets the order of work, and your outage windows set the dates of anything that needs a unit switched off.
Sampling across the fleet
Oil is drawn from every unit, normally with the transformer in service.
Analysis and interpretation
Each sample is tested to its published methods, and the results are read against the interpretation guides and the unit's own history.
Site tests where the findings point
The units singled out by their oil results or their records receive electrical diagnostics. These tests need the transformer de-energised, so they are planned into your outage windows.
Scoring and ranking
Every unit is scored, and the fleet is ranked by condition and risk.
The plan
Treat, rehabilitate or replace, unit by unit and in order of priority, with the evidence behind each call.
What follows
The plan becomes the scope of the next piece of work: oil treatment, refurbishment, or installing a replacement.
What you provide
The assets and the site
The organisation, the site, the number of transformers with their rating and voltage ranges, the situation and your timeline: what the enquiry form asks for.
Existing records
DGA results, oil analysis and test reports, sent as a reply to our acknowledgement. A result means more when it is read against the same unit's history.
Outage windows
When each unit can be switched off, whether a regulated outage plan or a load-shedding rota sets it. Tests and work that need a de-energised unit are planned into those windows.
Access to the site
Access, ground conditions, crane availability and supply, confirmed at the site survey before a price is fixed.
What the condition assessment report gives you
A ranked picture of the fleet
Every transformer placed by condition and risk, so the weakest units are known and the sound ones are left alone.
A record for each unit
Its results, the method behind each one, a condition score and an indication of remaining life.
A prioritised intervention plan
Which units to treat, which to rehabilitate and which to replace, in order, as the basis of a capital plan.
A baseline for trending
The first results become the reference that every later sample and test on the same unit is compared with.
Oil tests, diagnostics and the standards behind them
Every test in the assessment follows a published method, and the method is reported with the result. These are the standards the work and the report rely on; the full oil-test schedule is on the capabilities page.
| Standard | What it governs here |
|---|---|
| IEC 60475 | Sampling insulating oil for the general tests |
| IEC 60567 | Sampling for dissolved gas analysis, and the analysis itself |
| IEC 60599 | Interpreting dissolved gas results |
| IEEE C57.104 | Interpreting dissolved gas results where the specification is written to IEEE |
| IEC 60422 | Reading oil condition, and the action each result calls for |
| IEEE C57.106 | Reading oil condition where the specification is written to IEEE |
| IEC 60156 | Breakdown voltage |
| IEC 60814 | Water content, by Karl Fischer titration |
| IEC 62021-1 | Acidity |
| IEC 60247 | Dissipation factor and resistivity of the oil |
| IEEE C57.152 | Guide to diagnostic field testing of the transformer |
| IEC 60076-18 | Sweep frequency response analysis of the windings |
| IEC 60137 | Bushings: the nameplate values that measured capacitance and tan delta are compared with |
The detail on the capabilities page
Transformer condition assessment: common questions
What does a fleet condition assessment include?
Oil is sampled from every transformer in the fleet and analysed. The units the oil results or the records single out then receive on-site electrical tests. Each unit is scored for condition and risk and given an indication of remaining life, and the assessment ends in a plan that says which transformers to treat, which to rehabilitate and which to replace.
Which standards are the oil results read against?
Dissolved gas results are interpreted to IEC 60599, or to IEEE C57.104 where the specification is written to IEEE. Oil condition is assessed against IEC 60422, or IEEE C57.106. Each test is carried out to a named method — breakdown voltage to IEC 60156, water content to IEC 60814, acidity to IEC 62021-1 — and the method is recorded beside every result.
How are units chosen for on-site electrical testing?
Sampling covers the whole fleet first. Electrical tests then go where the findings point: a unit with a rising gas signature, high moisture or a history of close-in faults, and any unit whose records call for it. The list is agreed with you before site work is planned, because it sets the outage windows the assessment needs.
What does the assessment report contain?
For each transformer: the test results, the method each was carried out to, the reading against the relevant limit or interpretation guide, a condition score and an indication of remaining life. For the fleet: the units ranked by risk, and a plan setting out which to treat, which to rehabilitate and which to replace, in order of priority.
Can a fleet with no test history be assessed?
Yes. The first assessment then becomes the baseline that later results are trended against. Where earlier oil results, factory test reports or a previous frequency-response trace exist, they are used, because most of these measurements mean more when compared with the same unit's earlier values than when read alone.
What does a condition assessment cost?
It depends on the number of transformers, how many are tested on site as well as sampled, where the site is and what reaching it involves. We do not publish a price list: scope is confirmed on the ground before a price is fixed. The enquiry form asks for fleet size, ratings and site location, so that the first reply is specific to your fleet.
Scope this programme for your site
Tell us the assets, the site and the situation. The enquiry form opens with this programme already selected.