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Q4. a) What design factor limits the maximum torque of a d.c. motor? (6)

(b) A shunt motor runs on no load at 700 r/min off a 440 V supply. The resistance of the shunt circuit is 240Ω. The following table gives the relationship between the flux and the shunt current:

Shunt current (A):      0.5   0.75   1.0   1.25   1.5   1.75   2.0

Flux per pole (mWb): 6.0   8.0   9.4   10.2   10.8   11.2   11.5

Calculate the additional resistance required in the shunt circuit to raise the no-load speed to 1000r/min (10)