Transformer sizing worksheet calculator

Use this page when a transformer schedule, estimate or replacement note needs a clear kVA worksheet before a product or rating discussion is carried forward. The calculator adds active load rows, converts kW rows to kVA using the entered power factor, applies entered demand factors and then applies an entered spare margin.

The result is a project record. It is useful when a reviewer needs to see how each row contributed to the required kVA. It does not choose the transformer, decide ventilation, prove overload capability, set impedance, decide protection or replace transformer manufacturer data.

Load Row Use Cases

The row model is deliberately simple. It is not a standards table and it does not supply demand factors. It keeps the entered basis visible so another reviewer can challenge the rows before relying on the result.

Sizing Boundary

The required transformer kVA is only as strong as the entered rows. A row entered as kW must use a power factor that belongs to that load condition. A row entered as kVA should already be an apparent-power value from a schedule, equipment source or review record.

Transformer sizing also depends on duty, ambient conditions, cooling, load profile, harmonics, impedance, fault level, tap range, installation environment and product data. Those items sit outside this arithmetic worksheet. Keep the worksheet with the transformer schedule, selected product data and review notes rather than treating it as a final decision.

Formula Basis

For a row entered as kW, apparent power is:

text SkVA = kW / PF

For a row entered as kVA, the row value is used directly. The worksheet then applies the entered demand factor to each active row:

text Sdiversified = sum(SkVA x demand_factor) Srequired = Sdiversified + Sdiversified x spare_margin_% / 100

If an entered transformer size is provided, the comparison is:

text selected_margin = Sselected - Srequired selected_utilisation_% = Srequired / Sselected x 100

Review Workflow

1. Confirm that all rows belong to the same transformer sizing question.
2. Enter kW rows only when the power factor is known for that row.
3. Use kVA rows when the source already gives apparent power.
4. Enter demand factors from the project basis; do not treat them as hidden defaults.
5. Enter spare margin separately so future allowance is visible.
6. Compare a selected transformer size only after the load-row basis is traceable.
7. Carry the result forward with manufacturer data, duty and installation review.

Worked Records

Boundary With Related Calculations