Total copper loss is:

1985.8 W (armature 1185.8 W + shunt 800 W)

Efficiency uses total losses of:

copper loss plus iron and friction = 2085.8 W, giving 93.50%

Asked 2/21
2065 Chaitra (old course) · 8 marks

30 kW shunt generator: emf, copper loss, efficiency (100 W)

Short answer

Load current 150 A, shunt current 4 A, armature current 154 A. Generated emf E = 200 + 154×0.05 = 207.70 V. Copper losses: armature 1185.8 W, shunt 800 W, total 1985.8 W. Efficiency = 30000/(30000+1985.8+100) × 100 = 93.50%.

A dc shunt generator gives full load output of 30 kW at a terminal voltage of 200 V. The armature and shunt field resistances are $0.05\ \Omega$ and $50\ \Omega$ respectively. The iron and friction losses are 100 W. Calculate (i) generated emf (ii) copper losses (iii) efficiency.

For a shunt generator $I_a = I_L + I_{sh}$ and $E = V + I_aR_a$ .

(i) Generated emf

I_L = \frac{30000}{200} = 150\ \text{A}, \qquad I_{sh} = \frac{200}{50} = 4\ \text{A}

I_a = I_L + I_{sh} = 154\ \text{A}

E = V + I_aR_a = 200 + (154)(0.05) = 207.70\ \text{V}

(ii) Copper losses

\begin{aligned} \text{Armature copper loss} &= I_a^2R_a = (154)^2(0.05) = 1185.8\ \text{W} \\ \text{Shunt field copper loss} &= I_{sh}^2R_{sh} = (4)^2(50) = 800.0\ \text{W} \\ \text{Total copper loss} &= 1185.8 + 800.0 = 1985.8\ \text{W} \end{aligned}

(iii) Efficiency

Total losses $=$ copper loss $+$ iron and friction loss $= 1985.8 + 100 = 2085.8\ \text{W}$ .

\eta = \frac{\text{output}}{\text{output} + \text{losses}} = \frac{30000}{30000 + 2085.8}\times 100 = 93.50\%

Answer: (i) $E = 207.70\ \text{V}$ ; (ii) copper loss $= 1985.8\ \text{W}$ ; (iii) $\eta = 93.50\%$ .

✓ Answer checked by Claude Opus 5.5 (high effort)

30 kW shunt generator: emf, copper loss, efficiency · Electrical Machines, chapter 3 · asked 2×
EMF, copper loss and efficiency of 30 kW shunt generator · Electrical Machines I, chapter 3
EMF and efficiency of short shunt compound generator (50 A, 200 V) · Electrical Machines I, chapter 3 · asked 2×
EMF and efficiency of 20 kW compound generator · Electrical Machines I, chapter 3
Efficiency and engine BHP of 48.75 kW shunt generator · Electrical Machines I, chapter 3
EMF of short shunt compound generator (6 kW, 250 V) · Electrical Machines I, chapter 3
EMF of 25 kW short shunt generator with brush drop · Electrical Machines I, chapter 3
Armature dimensions of 50 kW shunt generator · Electric Machine Design, chapter 5
Main dimensions of 30 kW 220 V shunt generator · Electric Machine Design, chapter 5 · asked 4×
200 V shunt motor power, torque and efficiency · Electrical Machines I, chapter 4
Terminal voltage above emf and armature reaction · Electric Machines II, chapter 1

All Electrical Machines chapter 3 questions →

30 kW shunt generator: emf, copper loss, efficiency (100 W)

(i) Generated emf

(ii) Copper losses

(iii) Efficiency

Related questions