What we buy
Ranges we buy on this page
This guide explains percent impedance, its effect on fault current, and why two transformers with identical kVA ratings are not necessarily interchangeable. It is written for North Carolina plant engineers, utility asset managers, facility directors, and crews preparing equipment for removal.
| 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
Transformer impedance is the combined resistance and reactance that opposes current through the windings. Percent impedance expresses the voltage needed to circulate rated current during a short-circuit test, with one winding shorted.
The result belongs to a specified rating, tap position, and test reference temperature.
A nameplate marked 5.75% impedance does not mean the transformer loses 5.75% of its power. That figure describes its electrical opposition under defined test conditions.
Load losses appear separately on a test report, usually in watts, and voltage regulation also depends on the connected load’s power factor.
Local reality
Why it matters when you sell
When Transformer Buyers NC evaluates a used unit, the impedance figure helps establish whether its electrical characteristics are documented. A clear nameplate photograph should show percent impedance alongside kVA, primary voltage, secondary voltage, and serial number.
A factory test report can resolve a worn or unreadable plate.
Two 1,000 kVA transformers with the same voltage ratio can impose different fault duties on a downstream switchboard if their impedances differ. That distinction matters when assessing potential reuse.
Matching the pad dimensions and elbow interfaces alone does not establish that either unit fits the same electrical system.
Around the site
The numbers
For a three-phase transformer, rated secondary current equals kVA times 1,000 divided by the square root of three times secondary line-to-line voltage. A 1,000 kVA unit at 480 volts carries approximately 1,203 amperes at rated load.
Use the applicable nameplate rating when cooling stages provide multiple capacities.
With an assumed infinite primary source, secondary terminal fault current is approximately rated current divided by per-unit impedance. At 5.75%, that 1,000 kVA, 480-volt example gives about 20,900 amperes.
Actual calculations must include upstream source impedance, conductor impedance, motor contributions, and the fault location within the facility.
Where it sits
Common mistakes
Treating equal kVA as proof of interchangeability overlooks impedance, winding connection, phase displacement, and voltage ratio. Parallel operation requires a separate engineering review.
Unequal impedances can produce unequal load sharing, while incompatible ratios or phase relationships can cause circulating current even before useful load reaches the secondary bus.
Another mistake is copying a catalog figure into the removal paperwork instead of reading the actual nameplate or certified test report. Impedance can vary among designs with identical ratings.
Do not substitute insulation resistance, winding resistance, or a turns-ratio result for the transformer’s stated percent impedance.
On the ground
How it affects value
Impedance affects the unit’s suitability for reuse rather than providing a stand-alone measure of condition. A documented 5.75% figure is useful only alongside voltage ratings, winding configuration, and condition records.
A cracked bushing, leaking tank gasket, or failed winding still requires assessment regardless of the nameplate impedance.
Missing impedance documentation leaves an important electrical characteristic unresolved during evaluation. For an obsolete plant transformer in North Carolina, a serial-number-matched factory report can clarify the original design.
If the unit has been rewound, repair records and subsequent test results matter because the original nameplate may no longer describe it.
Local reality
What to do next
Photograph the entire nameplate straight on, then take a close image of the impedance entry and any tap diagram. Collect the factory test report, repair history, and most recent electrical test results.
Identify whether the transformer remains energized, has been disconnected, or has suffered a documented winding fault.
Before removal, have qualified personnel document the operating tap position and complete isolation under the site’s electrical safety procedures. Record the tank weight, oil condition records, lifting points, and access around the pad.
Transformer Buyers NC buys used, surplus, failed, and obsolete transformers throughout North Carolina, with documentation supporting evaluation.
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
Does lower impedance always make a transformer better?
No. Lower impedance generally allows greater terminal fault current for the same kVA and voltage under equivalent source conditions. It can also affect voltage regulation. The appropriate figure depends on switchgear interrupting ratings, protection coordination, load requirements, and any planned parallel operation.
Service area
Where should I find the percent impedance?
Look on the transformer nameplate for an impedance entry, often expressed as a percentage. Check the factory test report if the plate is damaged or incomplete. Match the report’s serial number, rating, and tap information to the actual unit before relying on that figure.
Payment
Can impedance alone establish available fault current?
No. Nameplate impedance supports an approximate transformer-terminal calculation, not a complete facility fault study. An engineer also needs utility source data, conductor lengths and sizes, motor contributions, and system configuration. A fault at a remote panel differs from one at the secondary bushings.
Logistics
How it affects value: what should a seller know?
Impedance affects the unit’s suitability for reuse rather than providing a stand-alone measure of condition. A documented 5.75% figure is useful only alongside voltage ratings, winding configuration, and condition records.