2. European distribution transformers losses and efficiency

The overall losses in EU-25 distribution transformers are estimated at almost 33 TWh. This corresponds well to previous studies, especially the Prophet Paper where the whole European losses in distribution transformers are estimated at 55 TWh. This calculation assumes no losses due to reactive power losses and harmonic losses in transformers. Our conservative estimate is that all these extra losses (due to reactive power loss and harmonics) are at least 5 TWh (or 15% of calculated total of no load and load losses) yearly for all; utility and private distribution transformers.

The table below presents the EU-25 losses in distribution transformers divided into three sectors. Both existing population and new annually sold units (market) are specified separately. No load losses account for almost 70% of total losses (ΣPk / ΣP ratios).

Total losses in newly (annually) purchased transformers are estimated at 1,24 TWh. Transformers purchased by utilities account for about 500 GWh of losses. Although utility transformers have rather lower rated losses than industrial, their overall running efficiency remains at similar level as industry operates higher ratings transformers which are more efficient in general, and additionally industrial transformers are loaded higher than utility transformers

Next figures present EU-25 + Norway countries details on utility distribution transformers losses (with load and no load losses division) and running efficiency of utility distribution transformers (both existing fleet and newly purchased units) across EU-25. The proportion of no load losses to load losses is close to ratio of 3 while the average EU-25 countries operating efficiency is 93,38%. It leads to general conclusion about focus on reduction of no load losses especially for small, lightly loaded transformers.

Other observations are that utilities in different countries have different losses approach. Still a lot can be done to reduce existing level of both no load and load losses. Analysis of situation in utility and industry does not lead to very clear trends. However two observations are following:

• Utilities pay more attention to reduction of losses in transformers than industry. However due to higher loading and larger units of industry population, the operating efficiencies remain at similar level.
• In very general, larger units are specified with lower rated losses. This trend is even more distinctly visible in case of load losses.

Clearly, as already explained transformer loading has very strong impact on transformer efficiency. In some countries, e.g. in Poland efficiency is lower than average because of excessive number of transformers (average load of 14,5%). We can speculate that some of these transformers are not actually energized and have been withdrawn from operation but still remain in inventories. Other hypothesis is that utilities are “helping” the system redundancy reserving some capacity for potential extra load in case of emergency. Also could be that users avoid too highly loading of transformers which are in poor technical conditions (e.g. moist insulation). EU 25 average utility load is 18,9%, peak load is 0,53, time of peak load is 0,36 and time of peak loss is 0,2. For comparison, EU 25 industry transformers are average loaded at 37,7%.

Next figure presents the level of rated no load and load losses of distribution transformers in oil type transformers (utility and private). These losses are referred (as percentage) to AC’ losses mix (according to HD428 [2] standard) or CkCo (new EN50464 [3] standard) for most typical ratings. It is visible that private transformers have higher rated losses. The effort to reduce rated losses is more visible in case of larger transformers while for smaller ratings the additional effort to minimize no load losses is noticeable. The EU average rated losses of distribution transformer population are between BA’ and AA’ levels (HD 428) while newly purchased transformers in average have losses slightly below AC’ level.