Direct-Current Dynamos Volume 2; Instruction Paper (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1911 Excerpt: ...the machine. G. Simonds, J. Dalemont.t H. M. Hobart, and A. I. M. Winetraubff have given methods for computing the lengths of winding necessitated by the different types, but the method usually employed by manufacturers consists simply in drawing the armature to scale, and laying off thereon a section of the winding, the requisite length of wire being then determined by actual measurement. In particularly important cases--for example, when a new type of machine is to be built in large numbers or sizes--a portion of a dummy armature core is made of wood and wound with the correct size of wire. The length thus employed for one section is then multiplied by the number of sections to obtain the total length of wire required. Armature Resistance. Having obtained the length of wire required for the winding, the resistance of the armature may be calculated from the formula wherein p is the resistance of a unit-length of copper of unit crosssection; Lw is the total length of the armature winding in the same linear units as p; c represents the number of circuits in parallel through the armature; and s is the cross-sectional area of the conductor in the same units as that upon which the value of p is based. A circular conductor one foot long and one mil (0.001 inch) in diameter is called a circular mil foot; and if composed of standard copper, it has at 20 centigrade a resistance of 10.35 ohms, and at 0 centigrade a resistance of 9.55 ohms. At any other temperature t, the resistance Rt is /?, = 9.55 (1 + 0.0042) (26) If we take as our basis of calculation a square conductor, the cross-section being a square each of whose sides is one mil long, we have a square mil foot, which has an area 4-r n times that of a circular mil foot. Hence its resistance is re-S-4, or 0.78...