SECTIONAL TRANSACTIONS.— G. 461 



induction corresponding to full modulation of the polarising force for a 

 typical range of silicon steel samples. It is suggested that this condition 

 might form an acceptable means of limiting the range of incremental 

 measurements for industrial purposes and that with such limitation the 

 problems of measurement would be considerably simplified. Graphs and 

 tables of results are provided to support this view. 



Mr. J. Greig and Mr, J. E. Parton. — Harmonic power in iron 

 testing. 



Currents and voltages which are more or less non-sinusoidal are, in general, 

 obtained in circuits employed to produce alternating magnetisation in iron 

 cores. Certain methods of power measurenaent which are of great con- 

 venience and utility in iron loss testing depend for their accuracy on the 

 attainment of closely sinusoidal variation of either the voltage or the current 

 involved in the measurement, and as this sinusoidal variation is an ideal 

 which can only be approached, it may be necessary, where such methods are 

 employed, to determine the range within which power measurements may 

 be made with any required degree of accuracy. 



The paper records the results of a number of tests in which an A.C. 

 potentiometer was employed to measure the iron loss in a ring specimen 

 under polarised conditions at a frequency of 50 cycles. The accuracy of the 

 potentiometer measurement was estimated from a comparison with the 

 indications of a quadrant electrometer used as a wattmeter. Theoretical 

 considerations suggested that the required information might be obtained 

 by a simple practical method involving a measurement of the harmonic 

 content of the exciting current. It was confirmed that a useful estimate of 

 the accuracy of a loss measurement by the potentiometer could be made in 

 this way. 



Mr. E. V. D. Glazier and Mr. J. E. Parton. — Relative measurements 

 on rings and cores in incremental testing. 



The paper is concerned with certain important practical aspects of mag- 

 netic testing which are bound to arise in connection with the drafting of a 

 British Standard Specification. Thus the possibility of using a transformer 

 stamping assembly in place of the usual ring assembly for the measurement 

 of the incremental magnetic properties of iron is discussed with the aid of 

 characteristic experimental data. The diflferences found in incremental 

 permeability and iron loss values as measured on rings and on transformer 

 cores of the same material vary with the degree of polarisation. They 

 cannot be entirely attributed to the unavoidable air gap present in the 

 transformer assembly. If fundamental data upon the iron itself are re- 

 quired, ring specimens are still considered essential, but, on the other hand, 

 it is found that good repeat accuracy is obtainable on the assembled trans- 

 former core specimen, so that results taken upon a given specimen can be 

 regarded as a reliable guide to the behaviour of the size of core concerned. 

 The effects upon incremental permeability of tightening the core clamps, 

 of re-assembling the specimen, of employing different sized cores of a given 

 material and of assembling with butt or interleaved joints are shown by 

 experimental curves. Finally the paper deals with the practicability of 

 dispensing with a search winding during routine loss and permeability 

 measurements. 



Afternoon. 



Visit to works of Messrs. Pye Radio Ltd. 



