LIST OF SYMBOLS xv 



P = power; watts. 

 P = permeance. 



P = pressure, pounds per square inch. 

 p = number of poles. 

 pi = number of electrical paths in parallel in armature winding. 



Q = quantity of electricity. 



q = specific loading of armature periphery (ampere-conductors per 

 inch). 



R = resistance (ohm). 



R = resistance of armature coil undergoing commutation. 



R = magnetic reluctance (oersted). 

 R" = resistance between opposite faces of an inch cube of copper 



(ohm). 



R c = brush contact resistance per square inch of contact surface. 

 Rd = radial depth of armature stampings below slots. 

 Ro = resistance at temperature zero degrees. 

 Rt = resistance at temperature t degrees, 

 pole arc. 



T = ratio : r- - r- 



pole pitch. 

 r = length of radius vector. 



S = number of turns in a coil of wire. 

 S = brush contact surface. 

 s = slot width. 

 s/. = space factor. 

 SI = ampere turns. 



(SI)a = armature ampere-turns per pole. 

 (SI) g = ampere-turns for air gap. 



T = temperature rise in degrees Centigrade. 

 T = number of turns in armature coil. 



T e number of turns in armature coil between tappings to com- 

 mutator bars. 



TB = number of inductors in one slot. 

 t = interval of time. 

 t = temperature (degrees Centigrade). 

 t thickness of magnet winding. 

 t = width of tooth. 

 t e = time of commutation. 

 tr = width of rotor tooth. 



V = peripheral velocity of armature centimeters per second. 

 V c = surface velocity of commutator centimeters per second, 

 t; = peripheral velocity feet per minute. 



Vc = peripheral velocity of commutator surface feet per minute. 

 v d = average velocity of air hi ventilating ducts feet per minute. 



