METHODS OF TESTING TRANSFORMERS. 123 



corresponding hysteresis loss in watts per cubic centimetre, and 

 multiplying this by the volume of the core in cubic centimetres, 

 the total hysteresis is determined. 



The eddy currents can be calculated from the formula 



(see 61, Chap. XI.), and the copper losses can be calculated for 

 any assumed output on calculating the resistances of the two 

 circuits. We then have 



assumed output 



assumed output + total losses 



We note that the iron losses per cubic centimetre may be written 

 (see 59 and 61)- 



k being a constant. 



Now, if the applied primary P.D. is constant, the product nB 

 is constant ; therefore we have 



w _k(nBf . 



10 16 



where P and Q are constants, if e is constant. 



Thus we see that the iron losses diminish as the frequency 

 increases. 



REGULATION OF TRANSFORMERS. 



78. One of the most essential features of a good transformer 

 is that the secondary terminal P.D. should remain constant, as the 

 secondary load varies. 



The causes which tend to bad regulation are (1) large primary 

 magnetizing current, (2) magnetic leakage, and (3) large secondary 

 internal resistance. 



The first and second are minimized by working at low induction 

 densities, and by having closed magnetic circuits. In modern trans- 

 formers there is very little leakage, owing to the fact that there is 



