Procurement
Transformer sizing calculator
Enter the load, the voltages and the construction. The calculator returns the standard rating, the currents and the loss ceiling, and sends the result to the quote form with every value filled in.
The rating
1250 kVA
- Apparent power needed
- 1,039 kVA
- Loading at that rating
- 83 %
- Rated current, secondary
- 1,804 A400 V
- Rated current, primary
- 65.6 A11 kV
- Next incomer frame
- 2,000 A
- Upper bound of the fault contribution
- 30.1 kAuk 6 %
- Real power at rated current
- 1,125 kWPower factor 0.9
- EU loss ceiling
- Pk ≤ 9,500 WP0 ≤ 855 W
- Next rating up
- 1600 kVA
kVA = kW × diversity × (1 + growth) ÷ power factor ÷ loading limit, then the next step of the standard series. Currents are S ÷ (√3 × U). The fault figure is the rated current divided by the impedance with an infinite upstream source.
Arithmetic on your inputs and on the standard series, not a design. The responsible engineer confirms the rating, the impedance and the protection, and the network operator confirms the connection. Availability, manufacturer, price and delivery are confirmed per project in a quotation.
How the rating is worked out
The connected load is multiplied by the diversity factor, because the loads on a site rarely all run at once. Planned growth is added, and the result is divided by the power factor to turn kilowatts into kilovolt amperes. Dividing once more by a loading limit below 100 percent leaves headroom the unit never uses in normal service.
The rating chosen is the next step of the standard series at or above that figure. Choosing a value between two steps usually costs more and takes longer without a technical gain, which is why the calculator never proposes one.
Transformer sizing chart for common loads
| Load | At power factor 0.8 | At 0.9 | At 0.95 |
|---|---|---|---|
| 100 kW | 125 kVA, 160 kVA | 111 kVA, 160 kVA | 105 kVA, 160 kVA |
| 200 kW | 250 kVA, 250 kVA | 222 kVA, 250 kVA | 211 kVA, 250 kVA |
| 300 kW | 375 kVA, 400 kVA | 333 kVA, 400 kVA | 316 kVA, 400 kVA |
| 500 kW | 625 kVA, 630 kVA | 556 kVA, 630 kVA | 526 kVA, 630 kVA |
| 750 kW | 938 kVA, 1000 kVA | 833 kVA, 1000 kVA | 789 kVA, 800 kVA |
| 1,000 kW | 1,250 kVA, 1250 kVA | 1,111 kVA, 1250 kVA | 1,053 kVA, 1250 kVA |
| 1,500 kW | 1,875 kVA, 2000 kVA | 1,667 kVA, 2000 kVA | 1,579 kVA, 1600 kVA |
| 2,000 kW | 2,500 kVA, 2500 kVA | 2,222 kVA, 2500 kVA | 2,105 kVA, 2500 kVA |
Each cell is the apparent power needed and the standard rating that carries it, with no diversity, growth or loading limit applied. The calculator applies those.
What the calculator does not decide
| Question | Who settles it |
|---|---|
| Motor starting and the voltage dip it causes | The designer, with the starting method of the largest motor |
| Harmonic loading from drives, UPS or inverters | The designer's harmonic assessment, which can change the specification |
| Impedance, vector group and tapping range | The designer and the network operator |
| Ambient temperature, altitude and enclosure derating | The designer, with the manufacturer's datasheet |
| Whether the connection can take the load | The network operator |
From the result to a quotation
The request button carries the rating, the voltage pair, the frequency, the construction, the installation and a summary of the sizing into the quote form. Nothing is sent until the form is submitted. Daverlan then checks the specification, raises anything missing, and puts it to manufacturers whose published range covers it.
A specification sheet can also be copied or printed from the result, for a tender or for the engineer who signs the design.
Common questions
What size transformer do I need for a 200 kW load?
At a power factor of 0.8 a 200 kW load needs 250 kVA, and at 0.9 or 0.95 it still sits under 250 kVA. With 80 percent as the loading limit the answer moves to 315 kVA. The calculator shows both once the loading limit is set.
Is the result a design?
No. It is arithmetic on the inputs and the standard series. The responsible engineer confirms the rating against motor starting, harmonics and ambient conditions, and the network operator confirms the connection.
Why does the calculator ask for the construction?
Because the EU loss ceilings differ between liquid immersed and cast resin units, and because the construction decides where the unit can stand. The ceiling shown is the legal maximum for the rating, not the value of a particular unit.
Related
Send us the requirement
Send the rating, the voltage and the destination, or submit the specification, drawing or nameplate. Anything missing is raised before it reaches a supplier.