DYNAMIC MEASUREMENTS ON ELECTROMAGNETIC DEVK Ks I \(\r> 



equation can represent the actual rise when the plot is as curved as this 

 one IS. The best that can be done is to approximate the more important 

 initial part with a straight line, and in this sense the new approximation 

 shows a good fit. 



A typical speed relay will have a value of Gc/G. around 2 and the range 

 from 1 to 10 covers all relays in this class. For a ratio of 2, the new 

 representation of flux rise is within 2 per cent of the actual rise, as 

 opposed to about 5 per cent with the earlier equation. For the ratio of 1, 

 the accuracies are 4 per cent and 11 per cent respectively. 



ACTUAL FLUX RISE 



NEW FIRST APPROXIMATION EQUATION 



0.5 



1.0 



1.5 2.0 



TIME,t/tt 



2.5 



3j0 



3.5 



Fig. 25 — Comparisons of equations for flux rise. 



