A $30$ hp$,240$ V$,1150$ rpm dc shunt motor operating at rated conditions

has an efficiency of $88\mathrm{.}5\%.$ The armature circuit resistance and field

circuit resistance are $0\mathrm{.}096$ and $93\mathrm{.}6$ respectively. Calculate the

following:

a$)$ The armature current

b$)$ The output torque

c$)$ The mechanical developed power

d$)$ The mechanical developed torque

e$)$ The external resistance required in series with the armature to limit

the starting torque to $200\%$ of rated torque

$3$EP$3$ Fall $2021$ Lec $6$ Dr$.$ C$.$ Tang $9$

If the load torque is now reduced to $40\%$ rated torque, find:

f$)$ The new armature current, Ia

g$)$ The new operating speed,

h$)$ The external resistance required in series with the armature to

maintain rated speed