Load Losses of Alternating-Current Generators

The circulating energy method is a form of input-output test which eliminates the errors due to the measurement of energy equal to the capacity of the machine. When two duplicate machines are available, the authors consider it the best of the four methods. The phase characteristic method is faulty, due to the difficulty of obtaining accurate wattmeter readings at the low power factors. The total short-circuit core loss agrees closely with the load loss by the circulating energy method for the 860-kv-a. and the 300-kv-a. three-phase generators. It is to be regretted that careful short-circuit core loss and circulating energy tests could not be made on several polyphase machines having a large short-circuit core loss, such as those on lines 6 and 11, Table I; and lines 3, 5, and 27, Table II. A single-phase short-circuit core loss taken on the 860-kv-a. three-phase generator mentioned above, showed unexpectedly high values. This led to the taking of a careful circulating energy test with a single-phase load. The close agreement of the two is shown in Fig. 11. The small number of careful tests which it was possible to make for this paper does not warrant any recommendation for the determination of load losses when but one machine is available. Investigations should continue until a rule can be established to cover such cases.