DYNAMIC MEASUREMENTS ON ELECTROMAGVKTIC PKVlf^KS 1459 



Part III — Applications 



NEED FOR DYNAMIC FLUX MEASUREMENTS 



The results of an experimental determination of dynamic flux rise 

 and decay in solid core electromagnets are of general interest. Analytical 

 solutions have been obtained for linear infinitely long rods or toroidal 

 shaped structures where geometric simplicity exists. These solutions 

 are in infinite series form. These solutions show that an elementary 

 perfect representation can not be expected, even for these simple cases. 

 Furthermore, an electromagnet has other factors which make any at- 

 tempt at an analytic solution impractical. Some of these are: 



(a) The magnetic material is non-linear. 



(b) The flux density is non-uniform because of leakage flux. 



(c) The varying geometry of the magnetic parts, including the neces- 

 sary gaps, make the boundary value problems unmanageable. 



(d) Motion of the armature during operate and release. 



These all lead to the conclusion that a quick and accurate method of 

 measuring dynamic flux changes is necessary for fundamental studies 

 of the dynamic behavior of electromagnets. 



As an example. Fig. 22 shows dynamic flux and current rise and decay 

 measurements made on the same relay used for the dynamic motion 

 studies. These data are plotted on semi-log graph paper as on such a 

 plot an exponential curve becomes a straight line. The current rise curve 

 shows the dip due to armature motion, ending abruptly when the motion 

 is completed. The flux rise curve starts off nearly as an exponential but 

 rises more rapidly after armature motion starts. 



Two decay curves are shown, one \vith an open circuit and one with a 

 contact protection network. Associated with the latter is the winding 

 current which flows through the network. In the open circuit case, even 

 without the effect of armature motion, the flux decay is not exponential. 

 The flux decay with the network has a somewhat oscillatory shape about 

 the open circuit curve. The current itself does complete one heavily 

 damped cycle. The reversed current flow is shown as a dashed curve. 



The decrease in flux after a short interval compared to the open circuit 

 case, demonstrates that such a network can decrease the release time as 

 well as afford contact protection. 



For more fundamental studies, it is better to study flux behavior with 

 the armature held fixed and avoid the motional effects. 



DYNAMIC FLUX DECAY AND DEFINITION OF EQUIVALENT CORE CONDUCTANCE 



Fig. 23 shows another measured flux decay curve with the armature 

 locked in the operated position. Also shown are two one-term exponential 



