Fig. 2,139.—Diagram of transformer system with individual transformers. The efficiency is low, but such method of distribution is necessary in sparsely settled or rural districts.

Individual transformers, that is, a separate transformer for each customer is necessary in rural districts where the intervening distances are great as shown in fig. 2,139.

Ques. What are the objections to this method of distribution?

Ans. It requires the use of small transformers which are necessarily less efficient and more expensive per kilowatt than large transformers. The transformer must be built to carry, within its overload capacity, all the lamps installed by the customer since all may be used occasionally.

Usually, however, only a small part of the lamps are in use, and those only for a small part of the day, so that the average load on the transformer is a very small part of its capacity. Since the core loss continues whether the transformer be loaded or not, but is not paid for by the customer, the economy of the arrangement is very low.

In the second case, where one large transformer may be placed at a distribution center, to supply several customers, as in fig. 2,140, the efficiency of the system is improved.

Ques. Why is this arrangement more efficient than when individual transformers are used?