ALTERNATING-CURRENT TRANSFORMER. 



current would vary in inverse proportion to the magnitude of the 

 field-vectors. If we kept O M not only constant, but also in the same 

 position, the locus of the vector OA would also be a semi-circle. 

 This is a very fertile principle, and it was called by Dr. Bedell the 

 method of reciprocal vectors. 



Let, in Fig. 42, the semi-circle having Oi as centre, represent the 

 locus of the primary field of the constant-current transformer, Oi 

 being the primary current Let 04 be numerically equal to 20, O 1* 

 to 50, and O i to 60. 



A current O I* = 50 produces a field equal to O I =60, hindering 



the flow of the current. Hence, if the field is only O 4 = 20, then a 

 current of - X 50 = 150 can flow through the transformer. This 



current is represented by O 4'. It can easily be shown that the points 

 I, 2, 3, 4 correspond point for point to the points i', 2', 3', 4', the 

 angle 301 being equal to 2'oi. 



Fig. 43 represents the circle O/, reciprocal to 0*. Angle O A is 

 equal to angle O t A. 



A concrete case will bring the matter into a more palpable form. 



149. A transformer or induction motor requires a magnetizing cur- 

 rent ' = 5 amp. We assume Vi = 0.91 and Vt = 0.80. The constant 



79 



