Dry-type transformer fan-assisted duty should enter the purchase specification with an explicit capacity statement: whether the offered output is continuous or time-limited, the conditions that apply, and the documents supporting it. Record the normal-load requirement separately from any peak or emergency allowance. If the supplier has only declared temporary capacity, procurement should not count that figure as confirmed continuous capacity.
AI-generated illustration of a dry-type transformer with blowers; not an actual HEAKOR product, facility or project, or evidence of rated duty.
This guide is for UK industrial EPC and procurement teams comparing three-phase MV/LV cast-resin transformer offers. Its purpose is to close the duty-related qualifications before order. The responsible electrical designer approves technical suitability; the purchasing record makes that decision and its supporting evidence traceable.
Separate the required duty from the offered allowance
The requirement and the supplier's answer belong in separate columns. Start with the project's normal continuous demand and identify any additional time-limited requirement. Then record what the supplier actually declares for the proposed transformer and cooling package.
Words such as “peak”, “emergency”, “overload” and “fan-assisted” need a defined meaning in that offer. Ask for the permitted loading, duration and other conditions where the duty is limited. Do not supply missing limits from a generic percentage or another transformer's catalogue.
There is a practical reason to keep this distinction visible. A UK dry-type forced-ventilation FAQ describes its particular fan option in terms of temporary loading. A UK distribution-transformer catalogue, on printed pages 14–15, expressly describes the listed fan option as peak/emergency capacity rather than continuous operation. These are product-specific examples, not a rule that every fan-assisted design has the same limitation, and not evidence of HEAKOR capability.
Dry-type transformer fan-assisted duty: acceptance record
Use one record to connect each requirement with the supplier's declaration, its evidence and any unresolved deviation. The following is a suggested procurement framework, not a standards-prescribed form.
| Item to close | Required supplier answer | Evidence or approval reference |
|---|---|---|
| Normal continuous load | Declared continuous output for the required load profile and stated conditions | Rating schedule or datasheet, with design reference and revision |
| Temporary duty | Permitted loading, duration, recurrence restrictions and applicable initial conditions | Supplier loading declaration or operating limitations |
| Included cooling package | Exact equipment included; distinguish fitted fans from future provisions | Offer scope and configuration drawing |
| Installation boundary | Applicable ambient, altitude, enclosure and installation assumptions | Design declaration and documented exceptions |
| Loss-comparison basis | Rating and reference conditions for guaranteed losses; auxiliary consumption where required | Loss schedule matched to the offer |
| Cooling unavailable | Supplier operating limitations and the reference for the project response | Operating document and designer-approved responsibility record |
| Technical acceptance | Outstanding deviations, closure evidence and approved document revisions | Named technical approver and procurement release record |
Add columns for the buyer's requirement, the document number, the open question and the person responsible for closing it. A blank supplier answer should remain “to be confirmed”. It should not become an assumed acceptance simply because the headline kVA figure is large enough.
Make package inclusion part of the rating answer
A duty declaration needs to identify the configuration on which it depends. A quotation for fitted cooling equipment and a quotation allowing future fan installation are different supply descriptions. Record which one is being purchased and whether the submitted duty evidence covers that arrangement.
Keep detailed control interfaces in the separate temperature-monitoring interface schedule. The duty acceptance record should reference that approved schedule rather than reproduce sensor, alarm and control details. This keeps changes visible without creating conflicting instructions in two documents.
Keep the loss basis separate from the larger capacity figure
Ask which rating and reference conditions the quoted losses use. In the catalogue example above, the nominal rating and guaranteed losses remain tied to the natural-air rating even though a temporary fan option is described. That statement applies to that offering; it should not be converted into a universal efficiency rule.
For the actual purchase, the designer and commercial evaluator should agree the comparison basis and ask each supplier to answer against it. Record auxiliary-power information if the evaluation requires it. Do not assume the losses quoted at one operating point describe a different load or cooling state.
Close a duty mismatch before order release
If the supplier's declared continuous capability does not cover the required normal duty, return the mismatch for a supported proposal and technical review. A larger temporary allowance does not close that deviation.
The same review should reopen if the project's operating pattern changes. A duty originally described as occasional may become routine or continuous during design development. Update the requirement revision, obtain the supplier's response and retain the technical approver's decision before procurement treats the offer as accepted.
Changes to the enclosure, cooling package or site assumptions also need to be checked against the accepted declaration. Use the existing high-altitude specification guide where elevation affects the project, and the room ventilation heat-data checklist for the building-services review. This duty record does not calculate either correction or room airflow.
Record who owns the cooling-loss response
The supplier's permitted operating limits and the site's response to unavailable cooling are separate deliverables. Ask who provides each and where the accepted answer is recorded. The response must be defined by the responsible project team, not inferred from the presence of a controller or fan.
Retain references to the relevant operating limitations and approved interface documents. This article does not prescribe protection settings, load-shedding logic or a field loading trial.
Check the final document set
Before release, reconcile the accepted quotation, duty schedule, configuration drawing, proposed nameplate information and operating limitations. Ask which thermal evidence supports the declared duty and verify its coverage of the proposed configuration. A document describing a different transformer or cooling arrangement needs an explicit applicability explanation.
Use the technical document centre to identify the records your enquiry needs. Document availability and scope require confirmation for the proposed equipment.
Frequently asked questions
Does “AF” by itself confirm continuous capacity?
No. The cooling description alone does not settle the permitted duty. Obtain the supplier's explicit declaration for the proposed design and conditions before accepting the higher figure against a continuous requirement.
Can an emergency allowance replace a shortfall in normal capacity?
Not without a revised declaration supporting the required normal duty and the designer's acceptance. Keep the shortfall open rather than treating a time-limited allowance as continuous output.
What if the offer includes provision for fans later?
Record future provision separately from equipment supplied now. Ask which duty the current delivery supports and what later configuration would require separate confirmation.
Should every supporting document repeat the whole schedule?
No. Documents can reference the accepted schedule, but their design identities, revisions and duty statements must agree. Resolve contradictory descriptions before release.
Submit your project specification
Review HEAKOR's dry-type transformer category, then Submit Your Project Specification. Include the required continuous load, any separate temporary duty, voltages, frequency, site conditions, enclosure requirements and requested evidence. Include the duty acceptance record with unresolved items identified. Equipment suitability, fan-assisted configurations, document availability and supply scope require project-specific confirmation.