

ARMATURE WINDINGS 263 



In connection with the predetermination of temperature rise, 

 the losses in the armature core may well be calculated on the 

 assumption that this condition is fulfilled. 



The vector diagrams should always be drawn to show the 

 relation of the variable quantities in one phase of the winding; a 

 balanced load being assumed. It does not then matter whether 

 the phases are star- or delta-connected, except that, in the case 

 of a star-connected generator, the vector OE t would stand for 

 the voltage between one terminal and the neutral point, and its 



numerical value would therefore be - 7? times the voltage 



between terminals. 



The length of the vector E t P in Figs. 99 and 100 is easily 

 calculated; but the numerical value of IX (the vector PE g ) 

 is not so easily estimated. Consider first what is to be under- 

 stood by the term armature reactance. 



86. Inductance of A.C. Armature Windings. It is not always 

 easy to separate armature reactance (X) from armature reac- 

 tion (the demagnetizing effect of the armature ampere-turns). 

 Both cause a drop of pressure at the terminals under load, espe- 

 cially on low power factors. By departing from the conventional 

 methods of treating this part of the subject, and striving to 

 keep in mind the actual physical conditions, by picturing the 

 armature conductors cutting through the flux lines, it is hoped 

 that the difficulties of the subject may, to a great extent, be 

 removed. 



The inductance of the windings, in so far as it affects regu- 

 lation, will be taken up again in Chap. XIV, and for our present 

 purpose which is mainly to design an armature that shall 

 not attain too high a temperature it is not proposed to add 

 much to what was said in Chap. VIII when treating of the flux 

 cut by the coil undergoing commutation. A distinction was 

 then made between the slot flux and the end flux. The same 

 conditions are met with in the alternator, where what is usually 

 referred to as the reactive voltage component (the vector E g P 

 in Figs. 99 and 100) is really due to the cutting of the end flux 

 by the conductors projecting beyond the ends of the slots: the 

 slot flux, being actually provided by the main poles, does not 

 enter the armature core below the teeth, and since the greater 

 part of it is not cut by the armature inductors, this portion of the . 

 slot flux which, in a later article, is referred to as the "equiva- 

 lent flux" should not be thought of as producing an e.m.f. of 



