A $200$ kW$,400$ V short shunt compound generator develops $375$ V on no$-$load when running at $1400$ rpm$.$ The speed of the machine falls to $1375$ rpm on full$-$load and terminal voltage rises to $400$ V$.$ If the increase in ux from no$-$load to full$-$load is $15\%,$ calculate the value of armature resistance. The series and shunt eld resistance are $0\mathrm{.}02$ ohm and $100$ ohm respectively. Assume brush contact drop as $1$ V$/$brush$.$