China’s standard GB 20052-2020 sets minimum energy performance for power transformers and divides them into three grades. Grade 1 is the most efficient; grade 3 is the minimum a new transformer must meet to be sold.
What is measured
- No-load loss: the loss in the core whenever the transformer is energised, whatever the load. It depends mainly on the core steel and core design.
- Load loss: the loss in the windings, which rises with the square of the load current. It depends mainly on conductor material and winding design.
Each grade sets maximum values for both losses at every standard rating and voltage class. A transformer is placed in a grade by comparing its measured losses with these limits.
Choosing a grade
A transformer runs 24 hours a day for decades, so small loss differences add up. A higher grade costs more to buy but less to run; the payback depends on your electricity price and how heavily the unit is loaded. Lightly loaded transformers benefit most from low no-load loss; heavily loaded ones from low load loss.
Outside China, the same thinking applies under other rules, for example the EU Ecodesign regulation for transformers. Tell us the standard your project must meet and we will check the losses against it before quoting.
Our product pages list the no-load and load losses for each rating, for example S20, S22 and SCB18.