What we buy
Ranges we buy on this page
Cooling classes describe how a transformer moves heat from its windings through insulating liquid or air to the surroundings. This guide explains ONAN, ONAF, OFAF and related codes, and how cooling equipment changes the kVA a unit can carry.
| Phase | kVA | Voltage | Fluid |
|---|---|---|---|
| 1-phase | 10 - 333 kVA | up to 25 kV | Liquid or dry |
| 3-phase | 25 - 10,000 kVA | 25 kV | Liquid-filled |
Who we buy from
Six kinds of seller
- Recyclers
- Electrical contractors
- Equipment dealers
- End users
- Demo contractors
- Distributors
Fast offers
A written offer the same business day, based on your photographs.
Dedicated logistics
Our own crew, trailer and crane, not a brokered haul.
No broker fees
One buyer from first call to cleared pad, with nothing skimmed.
How it works
Six steps from photograph to payment
- 01
Take pictures
Photograph the nameplate, the inside of the cabinet and the tank from both ends. Four frames on a phone are enough to price most units.
- 02
Send them to us
Email or text the photographs with the site address and whether the unit is still energised. We reply the same business day with questions or a number.
- 03
Review the offer
The offer names the unit, the site, the price and the pickup window. It is written, dated and good for thirty days unless the unit changes hands.
- 04
We schedule freight
A crew, a trailer and a crane if the pad needs one. You get the date and the arrival window, and the site does not have to close for it.
- 05
Testing on arrival
Winding resistance, insulation resistance and a turns ratio check, plus oil analysis where the unit is liquid-filled. Results travel with the unit.
- 06
Get paid
Payment is released against the signed bill of sale and the scale ticket, by check or ACH, with the paperwork copy left on site.
What we handle
The parts sellers dread
Rigging
Crane, skates and a route survey for anything that will not roll onto a trailer.
Oil containment
Pans, absorbent and a spill plan before a drain plug is touched.
Bill of sale
A document that clears a lien, a lease or a bankruptcy file, not a handwritten note.
PCB paperwork
Testing and manifesting for pre-1979 oil, handled before the unit moves.
On the ground
What it is
A liquid-filled cooling code has four letters. In ONAN, O identifies insulating liquid with a fire point at or below 300°C, usually mineral oil; the first N means natural internal circulation.
A identifies external air, and the final N means natural airflow across the tank or radiators.
ONAF keeps natural liquid circulation but adds forced air from fans. OFAF uses forced liquid circulation and forced air; ODAF adds directed liquid flow through designated winding paths. OFWF rejects heat through water-cooled exchangers.
Those distinctions identify hardware worth documenting before a radiator bank or pump skid is disconnected.
Local reality
Why it matters when you sell
A nameplate showing ONAN/ONAF ratings describes more than one operating stage, not interchangeable descriptions of the same capacity. If a North Carolina plant removes the fans before documenting the unit, the higher kVA rating cannot be evaluated from tank dimensions alone.
Photograph each rating and its associated cooling designation.
Missing fan motors, seized pumps or leaking radiator valves change the assessment of a used transformer. Transformer Buyers NC buys used, surplus, failed and obsolete units, but their condition must be described accurately.
Include cooling-control drawings and note whether the last operation used natural cooling or an assisted stage.
Around the site
The numbers
An illustrative nameplate might list 10,000/12,500/15,000 kVA for ONAN/ONAF/ONAF operation. The first rating applies without forced-air cooling; the next two correspond to specified fan stages. These numbers are an example, not a universal uplift.
Use the actual plate, including voltage, frequency and temperature-rise information, to identify each permitted operating stage.
Temperature rise is separate from cooling class: a liquid-filled plate may specify a 55°C or 65°C average winding rise under its stated conditions. Older North American plates often use OA, FA and FOA designations.
Dry-type equipment may show AA/FA or AN/AF; interpret those markings using the applicable manufacturer documentation.
Where it sits
Common mistakes
Do not describe the largest kVA number as the unconditional rating. A failed fan contactor, disconnected control supply or blocked radiator face can prevent the required cooling stage from operating.
Report the failed component and any alarm history rather than assuming that an intact tank means full nameplate capability.
Another mistake is treating every insulating liquid as mineral oil. KNAN and KNAF identify natural-circulation systems using liquid with a fire point above 300°C, often an ester. Confirm the fluid designation on the nameplate and fluid records.
Color alone does not establish chemistry, PCB status or compatibility with replacement liquid.
On the ground
How it affects value
Cooling class affects how we assess the equipment for purchase because it defines the hardware needed to support each rating. A complete ONAF assembly includes more than loose fans: guards, brackets, wiring, controls and sound radiator connections matter.
Identify detached components by transformer serial number before yard crews consolidate material.
Failure evidence matters more than the cooling acronym alone. Burned pump wiring, oil staining below a radiator flange or a winding-temperature trip deserves a clear description.
For a failed OFAF unit, distinguish an external cooling-system fault from suspected internal winding damage, and provide test reports if they already exist.
Local reality
What to do next
Start with readable photographs of the complete nameplate, cooling equipment and control cabinet labels. Record the serial number, every kVA stage, liquid type and known defects.
For a North Carolina removal, identify whether radiators, fans or a water-cooling skid remain attached and whether detached assemblies are clearly matched to the tank.
Have qualified personnel document isolation and the removal plan before anyone handles cooling connections. Radiator removal can involve trapped liquid, heavy assemblies and gasketed joints that need protection during transport.
Note lifting provisions, pad access and detached-component dimensions so the crew can plan rigging without mistaking a radiator bracket for a lifting point.
Get started
Get an offer in minutes
Five fields is all it takes. Photographs help, but a nameplate and a town are enough to start.
No fee, no obligation. We reply the same business day.
Tell us what you have
We reply the same business day.
Questions
Straight answers
Equipment types
Can an ONAF transformer run without its fans?
It may operate at its specified natural-cooling rating if its condition and operating requirements permit. The higher ONAF rating requires the designated fan equipment to function.
Service area
Does OFAF mean oil flows through directed winding paths?
No. OFAF identifies forced internal liquid circulation and forced external air cooling, but does not specify directed winding flow. ODAF identifies that directed arrangement. Use the manufacturer's cooling diagram to determine pump connections and internal flow paths rather than inferring them from exterior pipework.
Payment
Which cooling records should accompany a failed transformer?
Provide the nameplate photograph, cooling-control diagram, known fan or pump defects and existing alarm or test records. For water-cooled equipment, include exchanger leak history if documented.
Logistics
How it affects value: what should a seller know?
Cooling class affects how we assess the equipment for purchase because it defines the hardware needed to support each rating. A complete ONAF assembly includes more than loose fans: guards, brackets, wiring, controls and sound radiator connections matter.