$6$kW$,120$V$,1200$rpm Ra$=0\mathrm{.}2\backslash$Omega $,$Rfw$=100\backslash$Omega $.$ The machine is driven at $1200$ rpm and is separately

excited. The field current is adjusted at If $=0\mathrm{.}8$A$.$ A load resistance RL$=2\backslash$Omega is connected to the armature

terminals. Neglect armature reaction effect.

$($a$)$ Determine the quantity $\backslash$Phi for the machine.

$($b$)$ Determine Ea and la$.$

$($c$)$ Determine torque T and load power PL $.$

$4\mathrm{.}6$ The dc machine in Problem $4\mathrm{.}3$ has a field control resistance whose value can be changed from $0$ to

$150\backslash$Omega $.$ The machine is driven at $1200$ rpm $.$ The machine is separately excited, and the field winding is

supplied from a $120$ V supply.

$($a$)$ Determine the maximum and minimum values of the no$-$load terminal voltage.

$($b$)$ The field control resistance $($R$\_($fc$))$ is adjusted to provide a no$-$load terminal voltage of $120$ V $.$

Determine the value of R$\_($fc$).$ Determine the terminal voltage at full load for no armature reaction and

also if I$\_($f$($AR$))=0\mathrm{.}1$A