What to Include in a Transformer RFQ to Get Comparable Quotes

Procurement risk guide for buyers comparing transformer suppliers, documents, and manufacturing capability.

You send a transformer RFQ to five suppliers. You receive five quotations back — and none of them can be compared to any other. One quotes aluminum windings, another copper. One includes the loss capitalization value, another provides only the unit price. One quotes a 65°C temperature rise, another assumes 55°C. One includes freight to your port, another is ex-works.

This is not a supplier problem. This is an RFQ problem. The RFQ did not force every supplier to quote the same thing.

The Minimum RFQ Data Set

A transformer RFQ must include — at minimum — the following data fields. If any of these are missing, suppliers will fill the gap with their own assumptions, and every quotation will be based on a slightly different product.

Electrical Specification

Data field	Example	Why it matters
Rated power	500 kVA	The single most important number. Must be in kVA (not kW). Do not confuse kVA with kW unless the power factor is specified.
Frequency	60 Hz	Determines core flux density and therefore core dimensions, losses, and weight. A 60 Hz transformer is physically smaller than a 50 Hz unit of the same kVA.
Primary voltage	13.8 kV	Include the BIL (basic insulation level) if known: e.g., 13.8 kV, BIL 95 kV
Secondary voltage	480Y/277 V or 208Y/120 V	Specify the secondary voltage, connection, and neutral. 480Y/277 is three-phase, 480 V line-to-line, with neutral available.
Vector group	Must be explicitly stated (e.g., Dyn11, Dyn5, Yyn0, Dyn1)	If not specified, a supplier may quote its standard design, which may not match the buyer’s grid or parallel-operation requirements. Different markets and utility practices favor different vector groups — there is no universal default.
Tapping range	±2 × 2.5% (5-position off-circuit tap changer)	If not specified, you may get a transformer with no taps — or with the wrong range. For pad-mounted transformers, specify whether taps are accessible from the front (without removing the transformer from the pad).
Impedance voltage	5% (specify tolerance, typically ±10%)	Dictates fault current level and voltage regulation. A transformer with 4% vs 6% impedance at the same kVA produces very different downstream behavior.

Environmental and Operating Conditions

Data field	Example	Why it matters
Altitude	≤1000 m above sea level	Above 1000 m, cooling and insulation coordination must be de-rated.
Maximum ambient temperature	40°C	Combined with the transformer’s temperature rise, this determines the maximum winding hot-spot temperature and the insulation life.
Minimum ambient temperature	-25°C	Affects oil viscosity at startup and, for cold climates, may require oil heaters or a different oil specification.
Installation type	Outdoor, pad-mounted	Dictates enclosure type (ventilated, tamper-resistant), corrosion protection, and paint specification.
Environmental conditions	Coastal (salt spray, high humidity)	If the transformer will be installed near the coast, specify enhanced corrosion protection: C4 or C5-M paint system per ISO 12944.

Standards and Certification

Data field	Example	Why it matters
Design standard	IEC 60076	All quotations are based on the same design rules, test requirements, and tolerances.
Additional standards	Local utility specification, if any	A utility may have specific requirements for bushing spacing, fuse coordination, or compartment access that are not in the general standard.
Type test requirement	Type test reports required — specify whether independent laboratory reports are mandatory	Forces suppliers to disclose whether they have valid type test coverage for your rating.
Certification requirements	At minimum: ISO 9001. Additional: product-specific certifications (UL, CE, etc.)	Some certifications are legally required for the destination market. Others are buyer preference. Be explicit about which are mandatory.

Specification Traps

These are the most common ways an RFQ accidentally invites incomparable quotations:

Trap 1: “Or equivalent” without definition. If you write “copper windings, or equivalent,” every supplier will choose the interpretation that makes their price lowest. Define what “equivalent” means, or remove the “or equivalent” clause entirely.

Trap 2: Ambiguous temperature rise. “Temperature rise per standard” is not specific enough — different insulation classes have different allowable rises (65 K for Class A, 80 K for Class F, etc.). Specify: “Winding temperature rise ≤65 K, top oil temperature rise ≤60 K, per IEC 60076-2.”

Trap 3: Missing loss capitalization. If you care about losses (and for a transformer that will operate for 25+ years, you should care about losses), specify the loss evaluation formula in the RFQ. Without it, suppliers will quote the lowest-first-cost transformer — which is almost never the lowest total-cost transformer.

Trap 4: No definition of ‘accessories included.’ An RFQ that says “transformer with standard accessories” will produce a wide range of included equipment. Instead, list the accessories you require: pressure relief device, liquid level indicator, winding temperature indicator, drain valve, sampling valve, lifting lugs, grounding terminals, and nameplate. If the RFQ does not list them, the supplier will not quote them — and then you’ll be charged for them as extras.

The RFQ Checklist

Before sending your RFQ, verify that:

Important Note on Technical Values

The numerical thresholds, checklists, and acceptance criteria in this guide are procurement screening references. Final acceptance must follow the purchase specification, applicable IEC or IEEE standard edition, approved drawings, and the project-specific test protocol agreed between buyer and manufacturer.

Preparing an RFQ?

Send your draft specification. Our engineering team will review it for completeness — identifying missing data fields, ambiguous clauses, and specification traps that would produce incomparable supplier quotations.

[Submit RFQ specification for review →]

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