Question 7.4: Consider again the long-shunt compound dc generator of Examp......
Consider again the long-shunt compound dc generator of Example 7.3. As in Example 7.3, compute the terminal voltage at rated terminal current when the shunt-field current is 4.7 A and the speed is 1150 r/min. In this case however, include the effects of armature reaction.
As calculated in Example 7.3, I_s = I_a = 400 A and the gross mmf is equal to 5.9 equivalent shunt-field amperes. From the curve labeled I_a = 400 in Fig. 7.14 (based upon a rated terminal current of 400 A), the corresponding generated emf is found to be 261 V (as compared to 274 V with armature reaction neglected). Thus from Eq. 7.23, the actual generated voltage at a speed of 1150 r/min is equal to
E_a =\left( \frac{n}{n_0} \right) E_{a0}=\left( \frac{1150}{1200} \right) 261 = 250 V
Then
V_t = E_a – I_a(R_a + R_s) = 250 – 405(0.025 + 0.005) = 238 V
