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Unformatted text preview: DC Motors Numerical examples 1. A dc separately excited motor of 37.3 kW, 250 V, 1200 rpm has armature resistance R a = 0.2 . Its rated field current is I f = 2.17 A, and field winding resistance is R f = 115 . The motor when operating at full load (rated torque) is drawing an armature current I a = 200 A. The rotational losses are 4700 W. a) Find the rotor speed at no load. b) What is the current and the torque at standstill ( = 0). c) Draw the speedtorque characteristic of the motor. Solution: a) The rotor angular speed a a m E f V R I K  = . If f f I : , then E f f f K K I = . At no load: m f f V K I = Electromagnetic torque: em T f a T K I = Since f f I : , then em f f a T K I I = . Full (rated) torque: n n n P T = Rated power (on the shaft) of the motor: 37.3 n P kW = Since the rated angular speed: 2 2 1200 125.7 / 60 60 n n n rad s = = = The rated torque: 37300 296.8 125.7 n T N m = = The electromagnetic torque at full load: 37300 4700...
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This note was uploaded on 02/06/2012 for the course EE 4002 taught by Professor Scalzo during the Fall '06 term at LSU.
 Fall '06
 Scalzo

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