The distribution transformer is the final stage transformer in the power system, and its loss accounts for about 20% of the total loss. Energy-saving loss reduction in transformers is imperative. It can be said that the promotion of energy-saving transformers is of great significance for solving the tension in China’s power supply and building a conservation-oriented society. The development of transformers in China has gone through several stages, and the country’s emphasis on energy conservation has never changed. In the mid-1980s, the Chinese government mandated the use of S7 series low-loss distribution transformers to phase out the high-energy-consumption transformers operating in the power grid according to JB1300–73 and JB500–64 standards. Since 1998, the Chinese government has spared no expense in promoting the transformation of the two grids nationwide, replacing the S7 series with the S9 series distribution transformers. With the continuous advancement of technology and the continuous application of new materials and processes, new low-loss distribution transformers have been successfully developed. In the domestic distribution transformer field, there have been more energy-efficient S11, S13, S14, S15 series, as well as products with low loss such as amorphous alloy cores, which are even more energy-efficient than the S9 series.

The specific methods for the retrofitting of energy-saving transformers include four approaches: derating, maintaining capacity, increasing capacity, and adjusting capacity.

1) Winding modification methods: reducing capacity of high and low voltage windings; adjusting capacity of high and low voltage windings; maintaining capacity of high and low voltage windings; improving quality of high and low voltage windings; increasing capacity of high and low voltage windings.

2) Core modification methods: complete core replacement method; partial core replacement method; partial column core replacement method; complete ferrosilicon replacement method; partial ferrosilicon replacement method; increasing or decreasing the number of core columns method; increasing or decreasing the diameter of core columns method; single-sheet overlapping core method; overlapping method of core and silicon steel sheets; re-insulation method of core and silicon steel sheets.

3) Complete modification of winding and core: complete modification of winding, core capacity increase method; complete modification of winding, core capacity retention method; complete modification of winding, core capacity reduction method.

II. Ultra-low loss transformer

By utilizing * silicon steel sheets and optimized electromagnetic design, the no-load loss can be reduced by 30%, and the load losses can be reduced by 15% and 30% respectively. Major domestic * transformer manufacturers possess the production capability for such transformers. 3. Loss Analysis of Energy-Saving Transformers (1) Qualitative Analysis of New Energy-Saving Transformers The losses of a transformer include no-load loss, load loss, and additional stray loss. Generally, after the transformer is energized, the no-load loss remains a stable value, while the load loss is related to the load carried by the transformer and is directly proportional to the load capacity. The no-load and load losses of a transformer are expressed as equations (1) and (2) [3]: No-load loss: NL=P0+KQ0=P0+K(I0%Se・10-2) (1) Load loss: LL=(Pf+KQf)・β2=[Pf+K(Ud%Se×10-2)]・β2 (2) Q0 represents the rated excitation power of the transformer (kvar); P0 represents the rated no-load active loss of the transformer, approximately kW for iron loss; Pf represents the rated load active loss of the transformer, approximately kW for copper loss; K represents the reactive economic equivalent, generally taken as k=0.1kw/kvar according to the transformer’s position in the power grid; β represents the transformer load rate; I0% represents the percentage of no-load current; Ud% represents the percentage of short-circuit voltage; Se represents the rated capacity of the transformer, kV·A. Qf represents the rated load leakage power of the transformer, kvar. Compared to S7 transformers, new energy-saving transformers exhibit significant reductions in both no-load and load losses. 1) The losses of a transformer consist of no-load and load losses, with the load losses generally accounting for over 80% of the total transformer losses. 2) The energy-saving data for S11, S13, S14, and SH15 transformers compared to S7 transformers are as follows: no-load losses are reduced by 38%, 56%, 56%, and 78%, respectively; load losses: S11, S13, and S15 exhibit the same load loss reduction of 24%, while S14 shows a 36% reduction.

Replacing high-energy-consumption transformers not only saves transformer users significant electricity costs due to operational losses, but also contributes to energy conservation, resource utilization, and environmental protection for the entire society. Although updating high-energy-consumption transformers requires a considerable investment, the return on investment is quick. Considering both economic and social benefits, replacing S7 type transformers in the distribution network with more energy-efficient ones not only conscientiously implements the national spirit of energy conservation and emission reduction, but also enhances the safety and reliability of the distribution network.