DISTRIBUTION TRANSFORMER LOSSES: TYPICAL TRANSFORMER OPERATION What are the electrical losses that occur in distribution transformers?

Our discussions will focus on the losses that occur in electric utilities’ distribution transformers and how these losses differ from power transformers. Due to the significant number of distribution transformer that an electric utility uses, the analysis and understanding of losses that are present must be carefully considered.

A significant part of an electric utility’s total system losses takes place in distribution transformers. The primary reason would be because of the numerous units that are needed to cater the many types of consumers in the highly diversified service franchise areas typical of most electric utility.

The losses resulting from the large number of installed units are compounded because individual units need to be inexpensive, yet must carry the high amperages of utilization voltage levels. Furthermore, most electric utilities have in service many older distribution transformers designed when losses received less emphasis than in the present.

Most of the concepts of transformer operation were discussed in the Power Transformer section thus; most of the general ideas that are applicable to distribution transformers will no longer be repeated in this discussion. If this the first time that you visited this site, kindly refer to this link to read the brief discussion of the history and concepts of transformers.


Like any other transformer especially like power transformers, a distribution transformer whether it is a pole-mount or pad-mount contributes losses in the same way. These losses are also in the form of load losses and no-load losses.  Still, load loss is dependent on how the distribution transformer is utilize with respect to its loading and follows the I squared R rule. Also, No-load loss or core loss is the constant losses that are present in a transformer regardless of the loading and are primarily attributed to the core material. The only significant difference between the losses in a power and distribution transformers is the amount it can contribute individually.

Power transformers, due to its size obviously will contribute more losses than that of a single distribution transformer. However, due to the number of distribution transformer that exist in a system the total loss that distribution transformers makes it relevant.

Full use of the system-connected transformer capacity is important since transformer core losses occur continually while the transformer is energized. For example, in some cases, all the load on a transformer may be removed because of consumer abandonment of buildings, closed commercial establishments, etc. Although all meters are disconnected, the transformer may remain energized; thus, the occurrence of core losses on the transformer continues.

Besides core loss due to unutilized but energized distribution transformers, overloading of distribution transformers also greatly affect the losses that a certain distribution transformer contributes.

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