206 THE ROYAL SOCIETY OF CANADA 



Current Load, but even wilii full loud, and as small a Direct Current 

 as 27% of the Primary Alternating Cui-rcnt, tiie Phase Angle has 

 been increased from 1°-1 to over 12° and the Ratio from 80 to 84. 

 When the Direct Current is removed, there is a residual effect, which 

 may result in an increase at light load of Ratio of 2 to 5% and of 

 Phase Angle of 40 or 50%, both of which decrease with increasing load. 



Residual magnitism may be also imparted to the transformer 

 if the Secondary is opened under load or if a large Alternating Current 

 is broken in the Primary at other than the zero value. 



The most convenient way to eliminate errors due to this cause 

 is to open the Secondary and pass through the Primary full load 

 alternating current, which is then continuously reduced to zero. 



As an example of the distortion due to the Transient of Secondary 

 Current of a Series Transformer, Record No. 51, shows the current 

 flowing into one anode of a Mercury Arc Rectifier as recorded by 

 means of Resistance Shunts in the circuit and in the Secondary of 

 a Current Transformer. Due to the superimposed Direct Current, 

 the Phase Shift is large and hence the Secondary Current has a con- 

 siderable negative value when the Primary current reaches zero and 

 stops. This Secondary current dies away as a Single Exponentii>l 

 Transient. Record No. 50 gives a clearer representation of the 

 Secondary wave. 



In conclusion it may be stated that the Iron Clad Current Trans- 

 former does not introduce into the measurement of Symmetrical 

 Phenomena of equivalent Frequency of 20 — 100 cycles any serious 

 error which cannot be easily coi-rected as long as care is taken to not 

 unduly increase the Resistance and Reactance of the Secondary 

 Circuit. 



Resistance in particular is objectionable since both the change of 

 Ratio, and the distortion due to Phase Shift, depend upon it. 



External Reactance while affecting the Ratio has a corrective 

 effect on distortion. 



In the case of Transients the Secondary Current is of one degree 

 higher order than the Primary. 



When combinations of Transients, or of Transients and Permanent 

 Phenomena, occur they may be treated separately in the case of the 

 circuits of simple constants and the various components added to give 

 the final result. Not so with the Iron Clad Circuit, where the effects 

 of Saturation and Hysterisis have to be considered and the so called 

 circuit constants of Resistance and Inductance are really variables. 

 Unsymmetrical Phenomena, such as Rectified Waves and superimposed 

 Direct Current, introduce errors in Ratio and Phase Angle of un- 

 certain magnitude, and for which it is difficult to correct. 



