Question

A DC motor, when supplied from a 211 V power supply is observed to rotate under no-load conditions at 1,700 rpm. A stall test shows that the winding resistance is 1.65 ? The motor is connected to a load whose torque-speed characteristic is given by ? = ?×0.178. Find the speed (in rpm) at which the motor will drive this load. rpm (Give your answer in rpm to 3 s.f.)

Answer 1

The supply voltage is, V 211 V. And, winding resistance is, R, 1.65 Q No load conditions are, N, no-load1700 rpm The equation for voltage is, V = E, +1,R For no-load, I, -0, thus, V E Therefore, E, 211 V Since, oc Nno-load E And, E KN n0-load E K = Nno-laod 211 1700 =0.124

At stalling condition, E 0. Thus V E,+I,R S a 211 0 1(1.65) a I(1.65) 211 211 I 1.65 a - 127.88 A The torque equation is, T KI ax 0.178 - KI x 0.178= (0.124) (127.88) (0.124)(127.88) 0.178 - 89.08 rad/s 2πΝ therefore, Also, 60 2πΝ 60 2πΝ 89.08 60 (60)(89.08) N = 27T N 850.65 rpm