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Question: 03 the magnetization characteristic of a 250v 4kw dc series...

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03 The magnetization characteristic of a 250-V 4-kW dc series motor measured at 1500 rpm by separately exciting the series field winding is approximated as: E.-12.5where Lu, is the series field winding current. The armature and field winding resistances are .5Ω each and the armature reaction is negligible. The motor is supplied by a constant voltage source of 250 V and the rotational losses are given by Pror 0.2n, where n is the motor speed in rpm. (a) If the motor drives a load at a shaft speed of 1800 rpm, calculate the etectrical torque developed by the motor, the load torque and the efficiency (b) While producing the same electrical torque as in part (a), the motor speed is to be reduced to 1500 rpm by connecting an external resistor in series with the armature winding. What should the value of this resistance be? Calculate the motor efficiency.

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