Number of Transformers

Distribution substations are seldom provided along with a single transformer of needed rating (except pole mounted transformers/substations). Therefore, reliability of supply could be severely affected if only one transformer is used especially while it fails or while it is under maintenance. Reliability of supply increases along with increase within the number of transformers.

It is significant to note in which capacity requirement and hence cost per transformer reduces along with increase in the number of transformers, as the load gets divided, but the total cost increases as the relative advantages of reduction in the cost of each transformer is lower than the reduction in capacity.

However, there is additional cost for associated equipment for each additional unit of transformer. Thus, in order to optimize the reliability and the cost included, the number of transformers is usually kept among two to four. Transformers are required to comply along with the latest edition of IS 2026. The size specifications for this purpose are given in Table 1.

                                                   Table 1: Standard Sizes of Transformers