ALTERNATOR RECl'LATION AND OPERATION 



129 



emulation may be very poor, even if the current be the same in 

 the two cases. 



In the larger types of alternator, the large values of current 

 which result from short-circuit may cause serious damage to the 

 machine and to the system. The value of this short-circuit cur- 

 rent is closely related to the regulation of the machine, so that a 

 knowledge of the regulation is helpful in designing the circuit 

 breakers, switches, power-limiting reactances, etc. 



It is very desirable, therefore, to understand the factors and 

 the reactions which affect the regulation and the operation of 

 alternators. As it is usually impossible to obtain the requisite 

 loads for testing an alternator under actual load conditions, it 

 becomes necessary, in determining the regulation, to employ 

 methods which do not require the actual loading of the machine. 

 These methods will be described later. 

 61. Armature Reactance. When a current flows in the conduc- 



4 an alternator armature, magnetic lines are set up around 

 these conductors. Such lines are indicated around the conduc- 

 tors of one phase on a smooth-core armature, in Fig. 134. This 

 magnetic leakage flux linking with the current gives inductance 

 to the armature conductors. This inductance when multiplied 

 by '2- times the frequency 

 tin.- rtnclnncc of the 

 conductors. Therefore, al- 

 ternating current flowing 

 in these conductors will 

 encounter not only reiUh 

 tanre.but reactanceas well. Q Q Q 



bOWfl the 



' ving in a rather 



deep and narrow slut of an 



iron-Had armature. The 



current flowing in the>e conductors produces magnetic lines, 



path is across the slot and bark through the armature iron. 



"wn in the figure. The reluctance ,f ihi> !>ca! magnetic 

 circuit 1J. entirely in the *lnt itself. M< the relu.-ia- 



that part of t he pat h which lies in the iron i> practically negligible. 

 A deep nai-row -lot \\ ill allow more lin. dudor to 



it than the -hallow and wi 



e an alternator with deep narrow slots will have a much 



Armature 

 Leakage Flux 



Armature 



.1. Flux linki-<l with armature OOD- 

 iui-tors on .-moot li-ron- armature. 



