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III. On the Effective Inductance , Effective Resistance, and Self- 



- Capacity of Magneto Windings. Bi/ N. W. McLachlan, 



D.Sc.Eng. M.LE.E. (From the National Physical 



Laboratory.) * 



Synopsis. 



(1) Introduction. 



(2) Measurement of the Self-Inductance and Effective Resistance 



of the primary winding by Undamped Oscillations. 



(3) Measurement of the Self- Inductance and Effective Resistance 



of the secondary winding by Undamped Oscillations. 



(4) Measurement of the Self-Capacity of and Dielectric Loss in 



Secondary winding. 



(5) Bridge method of Measuring the Self-Capacity of Secondary 



winding. 



(6) Results of Experiments : — 



(a) Armature in Housing. 



(b) Armature out of Housing. 



(c) Effect of Polarization. 



(d) Effect of Armature Brass End-plates. 



(e) Effective Permeability. 



(/) Self-Capacity of Secondary. 

 (g) Dielectric Loss in Secondary. 



(7) Calculation of Energy Loss prior to the passage of the 



spark. 



(8) Alternative method of calculating the Energy Loss. 



(9) Comparison of methods used in (7) and (8). 



(10) Comparison of Loss with armature in and out of Housing. 



(11) The effect of an Air-core Inductance in the Primary circuit 



on the Damping. 



(12) Self-Resonance of the Secondary winding. 



(13) Effective Inductance and the Effective Resistance of iron- 



cored coils under Damped Oscillations. 



(14) Measurement of Effective Inductance and Effective Re- 



sistance of iron-cored coils under Damped Oscillations. 



(1) Introduction. 



TN the Phil. Mag. March 1919 Dr. N. Campbell published 

 some results of experiments on the high-tension magneto. 

 On p. 286 of this paper we find that a method of obtaining 

 the self-inductances of the primary and secondary windings 

 is describe*]. This yields the results given in fig. 3 and on 

 p. 293. From these it appears that the inductances of the 

 primary and secondary windings for damped oscillations 

 remain constant over a certain range of frequency up to 

 about 2500 ~ per sec. This is shown to hold good for a 

 Thomson-Bennett rotating armature magneto andfora B.T.-H. 

 polar inductor magneto. Now the inductance of a magneto 



* Communicated by the Author. 



Phil. Maq. S. 6. Vol. 41. No. 241. Jan. 1921. D 



