Section III., 1913. [189] Trans. R.S.C. 



Transient and Permanent Phenomena in Electric Series 

 Transformers. 



By Andrew McNaughton, M.Sc. 



Presented by Dr. L. A. Herdt, F. R.S.C. 



(Read May 28, 1913) 



" The use of the Current Transformer in connection with the 

 measurement of Transient and Permanent Phenomena." 



The Series or Current Transformer, consists of a Primary Circuit 

 through which the Line Current passes, and of a closely coupled 

 Secondary Circuit, insulated therefrom and closed through the cm-rent 

 coil of an Ammeter, Watt meter. Watt hour meter, or of a Relay. 



The object of the use of the current transformer is to insulate 

 the connected instruments from the line and to reduce the current 

 to a value convenient for measurement. 



In order to determine the Primary Current from the reading of 

 the Ammeter in the Secondary it is necessary that 



, , ^ . Primary Current , , 



the Ratio, . be known 



Secondary Current 



and it is desirable that this ratio remain constant and independent 

 of the current through the range of measurement. 



When the Current Transformer is used in connection with a Watt 

 meter for the determination of Power, or with a Watt hour meter 

 for the measurement of Energy, in addition to the Ratio, the Phase of 

 the Secondary Current with reference to the Primary must be known. 

 This angle should preferably be small and independent of the current. 



Furthermore, when the Primary Current contains Transients, 

 ■certain terms are introduced into the Secondary Current by the Trans- 

 former itself, and in connection with the Oscillograph it is important 

 to know the magnitued of, and the correction for the errors so involved. 



The ol:)ject of this paper is to discuss the errors introduced by 

 the use of Current Transformers in connection with Electric 

 Measuring and Recording Instruments. Both Transient and Per- 

 manent Phenomena are considered. 



The subject is developed mathematically on the assumption that 

 the circuits involved have constant Resistance, Self and Mutual In- 

 ductance and negligible Capacity. 



