Q5 A 500-V, 500-rev/min d.c. shunt motor has a full-load (rated) armature current of 42 A. Ra = 0.6 N and Rf = 500 Q. It is required to run the machine under the following conditions by inserting a...

Extracted text: Q5 A 500-V, 500-rev/min d.c. shunt motor has a full-load (rated) armature current of 42 A. Ra = 0.6 N and Rf = 500 Q. It is required to run the machine under the following conditions by inserting a single resistor for each case. (a) 300 rev/min while operating at rated electromagnetic torque; (b) 600 rev/min at the same torque; (c) 800rev/min while operating at the same gross power as in condition (b). For each condition, find the appropriate value of the resistor. The following magnetization curve was taken on open circuit at 500 rev/min: Field current 0.4 0.6 0.8 1.0 1.2A Generated e.m.f. 285 375 445 500 540V