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Procurement Guide
Transformer RFQ Checklist
A complete RFQ must include rated capacity, primary and secondary voltage, frequency, applicable standard, vector group, cooling type, and test requirements. The more detail you provide, the faster and more accurate your quotation will be.
Most delayed or inaccurate quotations come from incomplete enquiries. A vague request — "I need a 1000 kVA transformer, please quote" — cannot be priced without assumptions that may not match your project. This checklist covers every parameter a manufacturer needs to produce a technically compliant, comparable offer.
Electrical Fundamentals
Rated Capacity (kVA / MVA)
State the required rated output in kVA for distribution transformers or MVA for power transformers. If you are unsure, provide your maximum connected load and the manufacturer can advise on a suitable rating. Oversizing without reason adds cost; undersizing causes overloading and premature failure.
Primary (HV) and Secondary (LV) Voltage
Specify both voltages in kV or V. Include the system operating voltage — e.g. 11 kV HV / 0.4 kV LV — not just nominal nameplate values. If the HV system has a specific range (e.g. ±10%), state it. Incorrect voltage specification is one of the most common sources of re-work.
Frequency — 50 Hz or 60 Hz
This is non-negotiable. A transformer designed for 50 Hz cannot safely operate at 60 Hz without re-calculation (and vice versa). Most of Africa, Europe, the Middle East, Asia-Pacific, and China operate at 50 Hz. The Americas and parts of Asia operate at 60 Hz.
Number of Phases — 3-Phase or Single-Phase
The majority of distribution and power transformers are 3-phase. Single-phase units are used for specific applications such as railway traction, residential service drops (US style), and some rural distribution. Confirm this explicitly.
Standard and Configuration
Applicable Standard — IEC 60076 / ANSI / GB/T 6451
State which standard governs the design and testing. IEC 60076 is used in most of the world. ANSI/IEEE C57.12 is required for the Americas and some Asian markets. GB/T 1094 / GB/T 6451 is the Chinese national standard (closely aligned with IEC). If your project spec references a customer-specific standard, include it.
Vector Group — e.g. Dyn11, YNyn0
The vector group defines the winding connection (delta or star) and the phase displacement between HV and LV windings. Dyn11 is the most common for IEC distribution transformers. YNyn0 is used where LV neutral earthing is required. ANSI projects typically use Dy or Yd configurations. Specifying the wrong vector group can cause protection relay misoperation.
Impedance Voltage %
Short-circuit impedance (Uk%) affects fault current contribution and load sharing between parallel transformers. Distribution transformers are typically 4–6%. State the required value or let the manufacturer recommend one based on the system's fault level. If two transformers will run in parallel, their impedance values must be matched.
Cooling Type — ONAN / ONAF / Dry-Type AN / AF
ONAN (oil natural, air natural) is the standard for outdoor oil-immersed distribution units. ONAF adds fans for a higher rating in the same tank. Dry-type AN is fan-free; AF uses forced air cooling for higher ratings. State the cooling class or describe your installation constraints and let the manufacturer advise.
Tap Changer — OLTC or DETC, Range
On-load tap changers (OLTC) allow voltage adjustment under live load. De-energised tap changers (DETC, also called off-load or no-load tap changers) require the transformer to be switched off for adjustment. State the type and required tap range — e.g. ±2×2.5% (giving ±5% in four steps) or ±8×1.25%. OLTC adds significant cost.
Installation Environment
Indoor or Outdoor, IP Rating
Outdoor transformers require weatherproof construction. Indoor installations in clean, ventilated rooms have fewer enclosure requirements. For dry-type transformers, state the required enclosure IP class — e.g. IP21 for indoor, IP54 for dusty or humid environments.
Altitude and Ambient Temperature
At altitudes above 1000 m (IEC standard reference altitude), the reduced air density lowers the cooling capacity. Derating is required. Similarly, ambient temperatures above 40°C require derating or oversizing. This is critical for sites in East Africa, the Middle East, and highland regions of South America and Southeast Asia. Provide maximum ambient temperature and site altitude.
Required Accessories
Standard accessories for oil-immersed transformers include: conservator tank, Buchholz relay (detects internal faults via gas accumulation), winding temperature indicator (WTI), oil temperature indicator (OTI), pressure relief device, oil level gauge, and earthing terminals. State which accessories are required or reference a specification that lists them.
Test Requirements — Routine / Type / FAT
Routine tests (winding resistance, turns ratio, insulation resistance, no-load and load loss, applied and induced voltage) are performed on every transformer. Type tests (temperature rise, lightning impulse, short-circuit withstand) are done once per design. A factory acceptance test (FAT) is a witnessed routine test attended by your inspector. State which tests are required.
Commercial Information
- Quantity — Number of units. Larger orders affect pricing, lead time, and production scheduling.
- Required delivery date — Standard lead times for distribution transformers from China are 6–12 weeks ex-works. Power transformers and OLTC units take longer. State your delivery requirement early.
- Delivery port / destination country — State the destination port (e.g. Mombasa, Lagos, Santos) or destination country. This affects packing specification, incoterms, shipping cost estimates, and any country-specific certification requirements.
- Incoterms preference — FOB (buyer arranges freight), CIF (factory arranges to destination port), or DDP are the most common. State your preference or ask the supplier to quote on FOB.
Minimum Info vs. Full Specification
Not every enquiry requires a full technical specification. The table below shows what you need for a ballpark indication versus a formal, binding quotation.
| Parameter | Ballpark Price | Formal Quotation |
|---|---|---|
| Rated capacity (kVA/MVA) | Required | Required |
| HV / LV voltage | Required | Required |
| Frequency (50/60 Hz) | Required | Required |
| Standard (IEC/ANSI) | Required | Required |
| Phase count | Helpful | Required |
| Vector group | Not needed | Required |
| Impedance voltage % | Not needed | Required |
| Cooling type | Not needed | Required |
| Tap changer type & range | Not needed | Required |
| Accessories list | Not needed | Required |
| Test requirements | Not needed | Required |
| Altitude / ambient temperature | Not needed | Required for site-specific derating |
| Quantity | Helpful | Required |
| Delivery port / country | Not needed | Required for logistics cost |
Related Tools and Guides
Ready to Request a Quote?
Use our RFQ form to send your specification. The form prompts you for all the parameters on this checklist.
Send Your RFQ Ask a Technical QuestionQuick Checklist
- Rated capacity (kVA / MVA)
- HV and LV voltage (kV / V)
- Frequency (50 Hz or 60 Hz)
- Phase count (3Ø or 1Ø)
- Standard (IEC / ANSI / GB/T)
- Vector group (e.g. Dyn11)
- Impedance voltage %
- Cooling type (ONAN / ONAF / dry)
- Tap changer (OLTC / DETC, range)
- IP rating (if dry-type)
- Altitude and ambient temperature
- Accessories required
- Test requirements (routine / FAT)
- Quantity and delivery port
Product Ranges
Transformer Academy
Learning Path
Start with the plain-English basics, then move into RFQ, testing, standards, cooling, and calculator tools.