Hawkins Electrical Guide v. 08 (of 10) / Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications

by N. Hawkins

The erection of the machines is best accomplished by those making a specialty of this line of work, who by the nature of the undertaking acquire proficiency in methods of precision and an appreciation of the value of accuracy which is so essential in the work of aligning the machines, and which if poorly done will prove a constant source of annoyance afterward.

The attention required for the operation of the machines, embracing the running care and repair, is left to the "man in charge," who in most cases of small and medium size plants is the chief steam engineer. He must therefore, not only understand the steam apparatus, but possess sufficient knowledge of electrical machinery to operate and maintain it in proper working order.

The present chapter deals chiefly with alternating current machinery, the management of direct current machines having been fully explained in Guide No. 3, however, some of the matter here presented is common to both classes of apparatus.

Selection.—In order to intelligently select a machine so that it will properly harmonize with the conditions under which it is to operate, there are several things to be considered.

1. Type;
2. Capacity;
3. Efficiency;
4. Construction.

The general type of machine to be used is, of course, dependent on the system employed, that is, whether it be direct or alternating, single or polyphase.

Thus, the voltage in most cases is fixed except on transformer systems where a choice of voltage may be had by selecting a transformer to suit.

In alternating current constant pressure transmission circuits, an average voltage of 2,200 volts with step down transformer ratios of ¹⁄₁₀ and ¹⁄₂₀ is in general use, and is recommended.

For long distance, the following average voltages are recommended 6,000; 11,000; 22,000; 33,000; 44,000; 66,000; 88,000; and higher, depending on the length of the line and degree of economy desired.

In alternating circuits the standard frequencies are 25, and 60 cycles. These frequencies are already in extensive use and it is recommended to adhere to them as closely as possible.