72 Dr. McLachlan on Effective Inductance, Effective 



obtaining the self-resonance were used, one of which has 

 already been outlined. The other method of obtaining the 

 value of the resonant frequency is a combination of experi- 

 ment and calculation. The inductance can be measured 

 up to a frequency of 2500 — per second, and the self- 

 capacity is measured by the method described above in (4). 

 The value of the latter when the coil is shunted by a com- 

 paratively large condenser (say three or four times the 

 self-capacity of the coil) is assumed to be the same as 

 that at frequencies in the neighbourhood of the self- 

 resonance. Beyond /= 2500 ~ the inductance is obtained 

 by the method of calculation outlined previously in (3). 



Fig-. 19. — Curve used to obtain self-resonance of secondarv winding-. 



0-8 



0-6 



0-4 



0-2 



1000 ■ 2000 3000 4000 5000 6000 



Frequency ■ — per second. 



X = Resonance point. 



f = 5900 — . per sec. 



Armature in housing ; brass end-plates in place. 



Rotor position after full advance break, 



Thus, since values of L e2 and 3 are known for frequencies 

 from 2,500 — to 35,000 ~ the corresponding values of 

 o) 2 L e2 C 2 can be found. Plotting- &> 2 L e2 C 2 against frequency, 

 the curve shown in fig. 19 is obtained. The self-resonance 

 frequency occurs when GrL e2 2 = l, i. e. where the curve 

 meets the horizontal line AB. 



