5 b] A shunt generator delivers 50 KW at 250 V and 400 rpm. The armature and shunt field resistances are 0.02 Ω and 50 Ω respectively. Calculate the speed of the machine running as a shunt motor and taking 50 KW input at 250 V. Allow 1 V brush for
contact drop.

Solution:

Given

Generator = P_g =50W , V_t=250V , N_g=400rpm, R_a= 0.02ohm, R_sh=50ohm

motor = N_m= ? , P_m= 50KW , V_in= 250V , V_brush= 1V

we Know that

$E_{g}\propto N_{g}$ and $E_{b}\propto N_{m}$

For generator:

I_{sh}=\frac{V_{t}}{R_{sh}}=\frac{250}{50}=5A

I_{L}=\frac{P_{g}}{V_{t}}=\frac{50\times 10^{3}}{250}=200A

I_{a}=I_{L}+I_{sh}=5+200=205A

E_{g}=V_{t}+I_{a}R_{a}+V_{brush} \Rightarrow 250+205\times 0.02+1

E_{g}=255.1

For motor :

I_{L}=\frac{P_{m}}{V_{in}}=\frac{50\times 10^{3}}{250}=200A

I_{sh}=\frac{V_{in}}{R_{sh}}=\frac{250}{50}=5A

I_{a}=I_{L}-I_{sh}\Rightarrow 200-5=195 A

E_{b}=V_{in}-I_{a}R_{a}-V_{brush}\Rightarrow 250-195\times 0.02-1

E_{b}=245.1V

5 b] A shunt generator delivers 50 KW at 250 V and 400 rpm. The armature and shunt field resistances are 0.02 Ω and 50 Ω respectively. Calculate the speed of the machine running as a shunt motor and taking 50 KW input at 250 V. Allow 1 V brush forcontact drop.