How to determine cost-effective modes of use of transformers of two-transformer substations

The article examines the methodology for choosing an economic mode of operation of a two-transformer substation, including one or two transformers in operation (depending on the load).

The number of transformers included is determined by the condition that ensures minimum power loss in these transformers when operating in accordance with a given load schedule.

The power losses in a transformer are the sum of the losses in the core steel (no-load losses) and the losses in the transformer windings (short-circuit losses). The losses in the steel of the core do not depend on the load of the transformer, and the losses in the windings change in proportion to the square of the load (power S or current I). The rating data for this type of transformer gives the value of the short-circuit loss at the rated load.

The total power losses in one transformer at load S are determined by the relationship:

where S is the specified load; Sn — rated power of the transformer.

This dependence has the form shown in the figure (curve 1).

The total losses in two transformers of the same type with a common load S are determined by the relationship:

The dependence has the form shown in the figure (curve 2). When the value of Sgr. (limiting power) the power losses in one transformer and two switched on at the same time are equal.

The value of Sgr. can be obtained by the formula:

The value of Sgr is of great practical importance, as it allows you to choose the optimal mode of operation of the transformer substation. At load S less than Sgr, it is recommended to operate when one transformer is connected, when S is more than Sgr, it is recommended to connect two transformers. At the same time, a minimum of power and energy losses is achieved. The effect of reducing power losses can be evaluated by determining the difference in losses for the load S when one and two transformers are included.

Dependence of power losses on the load when one and two transformers are connected