There is no single efficiency number for Tier 2. EU Regulation 548/2014 sets maximum allowable no-load and load losses per rating class, and for larger units it sets a minimum Peak Efficiency Index (PEI). What counts as compliant therefore depends entirely on the rated power, the voltage class and whether the unit is liquid-immersed or dry-type.
In practice a modern Tier 2 distribution transformer sits well above 99 % efficiency at typical loading — but that headline figure is not what the regulation is written in, and it is not what you should specify against.
How the regulation actually expresses the requirement
For medium power transformers up to and including 3,150 kVA, the requirement is expressed as two loss ceilings in watts: a maximum no-load loss P0 and a maximum load loss Pk, tabulated per rated power and per voltage level. A design is compliant when it stays under both.
Above 3,150 kVA, and for large power transformers, the requirement is expressed as a minimum PEI instead — a single figure derived from the losses at the loading point where efficiency peaks. Consult the tables in the regulation itself for the value that applies to your rating; they are the legally binding source and they differ between liquid-immersed and dry-type designs.
Why no-load loss dominates the outcome
No-load loss is burned continuously, every hour the transformer is energised, whether it carries load or not. Load loss rises with the square of the current, so at partial loading it contributes far less than its rated value suggests.
A distribution transformer typically runs at 30 – 50 % average loading. At that duty, no-load loss can easily account for more than half of the annual energy wasted — which is why Tier 2 tightened it most, and why amorphous or high-grade grain-oriented core steel is where the money goes in a low-loss design.
An illustrative calculation
The figures the site uses elsewhere give a sense of scale. For a representative 1,000 kVA unit energised 8,760 h per year at roughly 40 % average loading, a Tier 2 design loses around 42 % less energy over its life than a comparable pre-EcoDesign design — about 410 MWh saved over 30 years, or roughly 144 t of CO₂ at 0.35 t per MWh.
Treat that as an example, not a specification. Real savings depend on your actual rating, loading profile, energy price and grid mix. The method is what transfers: annual energy loss equals no-load loss times 8,760 hours, plus load loss times the square of the average loading factor times 8,760 hours.
What to ask a supplier for
Ask for the guaranteed P0 and Pk in watts, the applicable tolerance under IEC 60076-1, and the routine test report showing the measured values for your unit. A declaration that a transformer "is Tier 2" without those numbers cannot be checked, and cannot be used in a total-cost-of-ownership comparison.
The practical trade-off is straightforward: lower losses cost more up front and pay back over 30 – 40 years of operation. If your energy price is high or the unit runs continuously, specifying below the Tier 2 ceiling usually pays. If it is a standby unit that is rarely energised, meeting the ceiling is enough. Give Protrafo your rating, voltage and expected loading and the comparison can be made in kilowatt-hours rather than adjectives.
