The figure shows the excitation curve (including residual voltage) of a 170 kW, 250 V DC shunt generator at rated speed of 850 rpm. The generator has negligible (0 W) armature resistance and a shunt field coil resistance of 50 W. The variable Field Control Rheostat in series with the shunt field coil has variable resistance in the range of 0 – 25 W. Answer the following questions and explain your reasoning for choosing the answer. (a) What is the approximate value of the critical field circuit resistance? (i) 95 Ω (ii) 85 Ω (iii) 75 Ω (iv) 65 Ω (v) 55 Ω (b) What is the induced EMF( Eo) at rated speed with the rheostat set to its minimum resistance? (i) 322 V (ii) 300 V (iii) 265 V (iv) 250 V (v) 50 V (c) What is the induced EMF( Eo) at rated speed with the rheostat set to its half way resistance? (i) 325 V (ii) 265 V (iii) 250 V (iv) 245 V
The figure shows the excitation curve (including residual voltage) of a 170 kW, 250 V DC shunt generator at rated speed of 850 rpm. The generator has negligible (0 W) armature resistance and a shunt field coil resistance of 50 W. The variable Field Control Rheostat in series with the shunt field coil has variable resistance in the range of 0 – 25 W.
Answer the following questions and explain your reasoning for choosing the answer.
(a) What is the approximate value of the critical field circuit resistance?
(i) 95 Ω
(ii) 85 Ω
(iii) 75 Ω
(iv) 65 Ω
(v) 55 Ω
(b) What is the induced EMF( Eo) at rated speed with the rheostat set to its minimum resistance?
(i) 322 V
(ii) 300 V
(iii) 265 V
(iv) 250 V
(v) 50 V
(c) What is the induced EMF( Eo) at rated speed with the rheostat set to its half way resistance?
(i) 325 V
(ii) 265 V
(iii) 250 V
(iv) 245 V
(v) 220 V
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