Comparing Transformer Quotations: Read the Loss Data Before Comparing Prices

Two quotations can specify the same kVA rating and voltage ratio while leaving important differences unresolved. A useful comparison records the loss values, their stated conditions and the way the transformer is expected to operate.

This guide explains a first-pass loss review for procurement teams. It does not establish interchangeability or replace a project-specific engineering assessment.

1. Start with comparable offers

Before entering figures into a spreadsheet, identify the exact model and revision behind each quotation. Use one project requirement sheet for all suppliers. Record any deviations separately so that a lower price is not mistaken for an equivalent scope.

Do not silently fill a missing field with a competitor’s value. Mark it “to be confirmed” and return the question to the supplier. Likewise, do not apply one reference temperature to every transformer technology without checking the applicable specification.

2. Separate no-load loss from load loss

At specified voltage and frequency, a simplified loss model treats no-load loss as present while the transformer is energised. Load-dependent loss is approximated by the square of per-unit current. For a steady operating point:

P_loss ≈ P₀ + k² × Pₖ

Here P₀ and Pₖ are in kW, and k is the operating current divided by rated current. At approximately rated voltage, the corresponding kVA loading fraction can be used as a screening approximation. Schneider Electric describes this square-law calculation for liquid-filled distribution transformers. Source: Schneider Electric loss calculation.

For this screening model, temperature effects, harmonics, voltage variation and auxiliary consumption are not modelled separately. A project evaluation must determine whether those effects are material; this calculation is not a cooling or protection design.

3. Why average loading can hide loss energy

Illustrative arithmetic only: the following figures are invented to explain the method. They are not Mingkong catalogue data, a quotation or a performance guarantee.

Assume a continuously energised transformer with P₀ = 1.0 kW and Pₖ = 10.0 kW, fixed comparison conditions, and the following annual current profile:

No-load energy is 1.0 × 8,760 = 8,760 kWh. Adding the two components gives 36,135 kWh of annual loss energy under these assumptions.

Using only average current would give 10.0 × 0.50² × 8,760 = 21,900 kWh of load-loss energy. That understates this example by 5,475 kWh. The reason is mathematical: averaging the squares is different from squaring the average. For changing duty, calculate each operating period and add the results.

Loss energy is only the transformer’s estimated loss contribution—not the total electricity consumed by the connected equipment. These hours also assume a 365-day year; use the actual energised hours and load schedule for your project.

4. Translate the comparison into purchasing questions

Ask the project team for a measured or planned load profile. If it is unavailable, prepare clearly labelled low, expected and high utilisation scenarios. Use the same assumptions for each offer. Do not present one scenario as a guaranteed saving.

At a flat energy tariff, estimated loss-energy cost is the calculated kWh multiplied by the applicable price per kWh. A lifetime comparison also needs a stated evaluation period and financial assumptions. Installation, maintenance, auxiliary energy and other scope differences should be assessed where relevant; they do not automatically cancel between offers. Schneider Electric discusses this broader ownership-cost approach. Source: Schneider Electric transformer ownership cost.

For time-varying tariffs, calculate the periods separately. Keep assumptions visible beside the result: operating hours, loading, tariff, exclusions and the date of the data. This makes a quotation comparison easier to revisit when the project changes.

5. Connect catalogue figures to acceptance evidence

A catalogue figure, a quotation guarantee and an individual-unit test result answer different questions. Request the document revision associated with the quoted configuration, and agree how the ordered equipment will be evaluated before purchase.

IEC 60076-19-1:2023 addresses uncertainty in measurements of no-load and load losses during routine power-transformer tests. Its scope underlines why measurement conditions and the agreed acceptance basis matter. Citing the standard does not establish that a particular Mingkong product has been certified or tested to it. Source: IEC official standard description.

A practical enquiry package

Send the following information together so that the loss comparison can be discussed alongside the equipment requirements:

• Selected model and catalogue page, or the existing nameplate and specification.
• Required capacity, voltages, frequency, project country and quantity.
• Expected energised hours and available load profile.
• Installation conditions and the relevant single-line or interface drawing.
• Requested loss guarantees, tests, documents and delivery requirements.
• Any unresolved items, explicitly marked “to be confirmed”.

Browse the current Mingkong Transformer Selection Guide, then send your project requirements. James can discuss the available information and coordinate clarification of the selected configuration.

Enquiries: salesjames@mkelecsolution.com