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 carries the result into the quote form with every value filled in.
Answered within one business day Requests stored in the EU Manufacturers get the specification, not your details No account, no obligation
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 calculator multiplies the connected load by the diversity factor, because the loads on a site rarely all run at once. It adds planned growth, then divides by the power factor to turn kilowatts into kilovolt amperes. A loading limit below 100 percent leaves headroom the unit never uses in normal service.
The rating is the next step of the standard series at or above that figure. A value between two steps usually costs more and takes longer with nothing gained technically, so 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.
Decisions beyond the arithmetic
| 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 |
UK and Gulf limits on the result
In the UK, the transformers a network operator adopts are specified to ENA TS 35-1, which runs from 25 to 2000 kVA; a larger result is specified outside it, to the owner's own document. In the Gulf, the rating has to hold at the site's heat. IEC 60076-2 lowers every temperature rise limit by the amount a site exceeds 40 °C maximum, 30 °C in the hottest month or 20 °C over the year, and Kahramaa specifies 55 °C, 40 °C and 30 °C for Qatar.
For the secondary, Great Britain's ESQCR fix the declared low voltage at 230 V, 10 % above or 6 % below, and one UK network operator lists its transformer ratio as 11000/433-250 V to help provide it.
From the result to a quotation
The request button carries the rating, the voltage pair, the frequency, the construction, the installation and the sizing summary into the quote form. Nothing is sent until you submit it. Daverlan then checks the specification, asks for anything missing and puts it to the manufacturers whose range covers it.
You can also copy or print the result as a specification sheet, for a tender or for the engineer who signs the design.
Questions buyers ask
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 your inputs and the standard series. Your 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?
The EU loss ceilings differ between liquid immersed and cast resin units, and the construction decides where the unit can stand. The ceiling shown is the legal maximum for the rating, and each offer declares the losses of its own unit.