Question 16.12: The magnetization characteristics of a DC shunt machine at t......
The magnetization characteristics of a DC shunt machine at the speed of 1150 rpm are illustrated in Fig. 15.2. The machine is operated as a motor and supplied by a 215 V power source. The no-load speed of motor is 1075 rpm. Determine the field winding resistance.
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1) 53.75 Ω
2) 86 Ω
3) 182.73 Ω
4) 195.45 Ω
The magnetization characteristics of the shunt DC motor at the speed of 1150 rpm are illustrated in Fig. 16.12. In addition, based on the information given in the problem, we have:
V_{t}=215\ V (1)
n_{FL}=1150\ rpm (2)
n_{NL}=1075\ rpm (3)
The equation of the second segment of the magnetization characteristics of machine at the speed of 1150 rpm can be determined as follows:
E_{a,FL}=10I_f+190 (4)
Moreover, the equation of the second segment of the magnetization characteristics of machine at the speed of 1075 rpm can be updated as follows:
E_{a,NL}=(10I_f+190)\frac{1075}{1150} (5)
As we know, in the no-load condition, we have:
E_{a,NL}\simeq V_t=215\ V (6)
Solving (5) and (6):
215=(10I_f+190)\times \frac{1075}{1150}\Rightarrow I_f=4\ A (7)
Applying Ohm’s law for the branch of field winding:
R_f=R_{fw}+R_{fc}=\frac{V_t}{I_f}=\frac{215}{4}\Rightarrow \pmb{R_f=53.75\ \Omega}
Choice (1) is the answer.
