Transformer losses explained: S11 vs S13 vs amorphous
No-load and load losses decide what a transformer really costs over 25 years. How the efficiency levels compare, with real catalogue numbers.
By Xinya Power editorial team
A distribution transformer runs for 25 years or more, so its losses usually cost more than the transformer itself. Understanding the two kinds of loss is the fastest way to compare offers.
No-load loss (iron loss)
Produced in the core every hour the transformer is energised, whatever the load. It depends on core material and design. On lightly loaded networks — rural feeders, residential areas at night — it dominates.
Load loss (copper loss)
Produced in the windings and rises with the square of the load current. It matters most for heavily loaded industrial units.
How the efficiency levels compare (10 kV, 400 kVA, oil-immersed)
| Series | No-load loss | Load loss | |---|---|---| | S11 | 570 W | 4,520 W | | S13 | 410 W | 4,520 W | | SBH15 amorphous | 200 W | 4,520 W |
Moving from S11 to amorphous saves about 370 W around the clock — more than 3,200 kWh per year for one transformer.
How to compare offers fairly
- Compare losses at the same reference temperature (75 °C for oil, 120 °C for dry type).
- Ask for guaranteed values with tolerances and the penalty basis, not "typical" values.
- Use a loss capitalisation formula: total cost = price + A × no-load loss + B × load loss, with A and B from your energy price and load profile.
- Check the type-test report that proves the design meets the declared losses.
Need a loss evaluation for your tender? Send us the A/B factors or your energy tariff and we will return a costed comparison of S13, SCB13 and amorphous options.
