GENERAL THEORY OF THE TRANSFORMER. 235 



equal to E' 'M ', so that 



P 4- P 



^,=^p 0) 



Wattless component M w . Knowing the maximum flux density 

 in the transformer core (see Art. 101) the permeability of the 

 iron may be found from permeability tables or curves and the 

 magnetic reluctance e/2 of the magnetic circuit of the transformer 

 may be calculated from the known dimensions of the core. The 

 product of this magnetic reluctance by the maximum core flux 

 4> gives the .maximum magnetomotive force required to mag- 

 netize the core, and this is equal to 47r/io times N f times the 

 maximum value of the wattless component (\/2M w ). That is 



from which we have 



Admittance* corresponding to magnetizing current. The value 

 of the magnetizing current of a transformer is very nearly inde- 

 pendent of the value of the load current /' which flows through 

 the primary coil, very much as if the magnetizing current flowed 

 through a circuit of definite admittance g l jb v connected in 

 parallel with the primary coil of an ideal transformer. That is 

 to say, a transformer which takes a definite magnetizing current 

 is equivalent to an ideal transformer with a certain circuit shunted 

 across its primary coil. The conductance g l is that factor which 

 multiplied by E f gives the power component of the magnetizing 

 current, and the susceptance b l is that factor which multiplied 

 by E' gives the wattless component of the magnetizing current. 

 That is 



* The shunt circuit which is imagined to be connected in parallel with the primary 

 coil of an ideal transformer to represent the effect of core reluctance, could of course 

 be specified in terms of impedance (resistance and reactance) instead of in terms of 

 admittance (conductance and susceptance), but specification in terms of conductance 

 and susceptance is to be preferred. See Arts. 29 and 46. 



