Transformer Voltage & kVA Guide
A transformer described only as “480 volt” or “75 kVA” is not fully identified. Its capacity, primary voltage, secondary voltage, phase, and winding connections describe different characteristics. Preserving those details helps a buyer distinguish your equipment from a similar-looking unit. Surplus Valve Buyer is an independent Houston-based surplus equipment purchase review business. We review reusable used transformers and new surplus equipment case by case. This guide explains how to describe the transformer you have, not how to select, connect, or install one. You can start with a short phone call or email; complete specifications and optional photos can follow.
Keep the equipment identity attached to its ratings
Use the manufacturer's nameplate rather than a warehouse nickname or an old project description. Copy the manufacturer, catalog or model number, and serial number when available. These identify the particular unit behind the voltage and capacity figures. An original specification sheet can help, but make sure it belongs to that transformer.
Keep each unit’s nameplate description separate. Similar enclosures may have different ratings. Report missing or unreadable plates rather than substituting assumed specifications.
kVA is capacity, not a kW claim
Kilovolt-amperes, abbreviated kVA, describe apparent power. Kilowatts, or kW, describe real power. The relationship depends on the load's power factor. Schneider Electric's transformer FAQ explains that a load stated in kW also needs its power factor to determine kVA. The two units should not be substituted in a seller description.
If the transformer plate says 75 kVA, report 75 kVA—not 75 kW. A motor rating, generator rating, or facility demand figure is not a replacement for the transformer's own rating. This distinction identifies equipment; it does not determine what load a future installation can safely supply.
Report primary and secondary voltage separately
A voltage pair describes both sides of the transformer. In a manufacturer's step-down description, primary identifies the input-side rating and secondary identifies the output-side rating. Keep those labels with their values instead of sending one voltage alone. Copy the complete notation, including any Y, slash, multiplication sign, or connection wording.
Do not reverse primary and secondary to suggest another purpose. The building’s voltage does not establish the transformer winding connection. Report documented ratings and uncertainty about previous use.
Example: 75 kVA, 480 V delta to 208Y/120 V
Eaton's transformer application guide gives a specific example of a three-phase, 75 kVA transformer rated 480 V delta primary and 208Y/120 V secondary. The notation 208Y/120 identifies a wye secondary with nominal 208 V line-to-line and 120 V line-to-neutral. Those are two voltage descriptions of that secondary, not separate capacity ratings.
The description “75 kVA, three-phase, 480 V delta primary, 208Y/120 V secondary” is clearer than “480-to-120 transformer.” This manufacturer example neither identifies your unit nor promises acceptance.
Delta and wye describe winding connections
Delta connects three windings in a closed triangle. Wye, also called star, joins one end of each winding at a common point. These terms describe connection arrangements; they do not mean used, new, dry-type, or liquid-filled. A delta-wye description identifies different arrangements on the two sides.
Keep the connection diagram with the nameplate information if it is already available in your records. Do not treat a 480 V delta description as identical to 480Y/277 V. The shared 480 figure does not erase the other notation. No wiring changes or electrical measurements are needed for an initial inquiry.
Phase and frequency remain separate fields
Record whether the transformer is single-phase or three-phase and copy its frequency in hertz, or Hz. A capacity number does not establish either field. Eaton's general-purpose guide separates single-phase and three-phase equipment, while its application guidance explains that frequency affects transformer operation.
A three-phase source at the former facility does not, by itself, prove that every transformer there is three-phase. Use the unit's marking. Matching kVA alone also does not make equipment interchangeable across voltage, phase, frequency, or connection differences. Any future application requires its own qualified technical review.
Example: a 12,470 V primary does not identify the construction
Schneider Electric's official listing for 750T45H describes a 750 kVA dry-type transformer with a 12,470-to-480 V rating. This example demonstrates why a medium-voltage primary should not automatically be described as an oil-filled pad-mounted transformer. Voltage and construction are separate characteristics.
Preserve 12470 as 12,470 V rather than rounding it. Copy additional connection notation from your plate; this product title does not establish a wye secondary. Manufacturer names identify sources, not Surplus Valve Buyer affiliations.
Preserve taps and other distinguishing markings
A nameplate may show taps, impedance, winding material, temperature rise, or an enclosure designation. These details help distinguish units with otherwise similar headline ratings. Copy them as marked, retaining units and percentages. If you have several documents, note whether they are manufacturer data or later test records.
Tap markings do not establish an arbitrary voltage range. Do not move connections for a sales description or infer copper windings from appearance. Leave undocumented fields unknown.
Condition and fluid records affect the review
Correct ratings do not establish condition. Describe whether the unit is unused surplus, removed from service, or of unknown operating history. Mention known damage, leaks, missing parts, and existing test reports. For liquid-filled equipment, provide available fluid identification, PCB analysis, and service records; eligibility is case by case.
EPA rules include concentration assumptions for undocumented equipment. Under 40 CFR 761.2, testing or manufacturer evidence combined with service-fluid documentation can establish PCB concentration. Age alone is not proof of actual concentration or zero PCBs. Do not drain, strip, or sample equipment for an inquiry; environmental assessment belongs with qualified professionals.
Start with a short message, without unsafe access
Contact us with the ratings you already know, quantity, general condition, and location. Optional nameplate and exterior photos can follow when safely available. If access is restricted or the plate is inside an electrical compartment, explain that instead of opening equipment for a picture.
Qualified personnel must handle electrical work and verify safe conditions under applicable procedures. OSHA requires qualified-person verification of deenergization and restricts work on energized equipment. This guide is not a safety procedure or installation specification. Purchase eligibility and any handling arrangements require review; neither a matching kVA nor a familiar voltage guarantees an offer.
