TRANSFORMER ON OPEN SECONDARY CIRCUIT. 93 



iron, insulated from one another by means of thin paper or varnish. 

 Sometimes the oxidization on the surfaces of the iron sheets is of 

 itself sufficient insulation. The core is laminated by planes 

 parallel to the magnetic flux. P3y this means the eddy currents 

 are confined to narrow paths, which greatly reduces them, and 

 minimizes the consequent loss of energy. 



The losses due to eddy currents will be more completely dealt 

 with later on. 



When working on open secondary circuit the power given to 

 the primary is equal to the sum of the losses due to hysteresis and 

 eddy currents, together with an insignificantly small ii 2 i\ loss, 

 which may be neglected. We shall see later that the iron losses 

 are independent of the secondary load. 



The function of the wattless component of the primary current 

 is to magnetize the iron. No permanent expenditure of energy is 

 required for this purpose. The magnitude of the wattless com- 

 ponent depends upon the permeability of the iron and the re- 

 luctance of the magnetic path. It is greater in open than in 

 closed magnetic-circuit transformers. 



Some writers on the subject call the total primary current, on 

 open secondary circuit, the magnetizing current ; but it is better, 

 in our opinion, to call the wattless component only the 

 magnetizing current. 



The power component is called the hysteretic energy 

 current. 



Denoting the magnetizing current and the hysteretic energy 

 currents by i m and i h respectively, and the total current by t , we 

 have 



since i h and i m are at right angles to each other. 



Let EQ be the E.M.8. value of the E.M.F. required to balance 

 the primary counter E.M.F., and write 



P = Wr (2) 



(3) 



fl 



and 



Y =-%. w 



