Consider the long-shunt, 250-V, 100-kW dc machine of Example 7.3. Assuming the machine is operated as a motor at a constant supply voltage of 250-V with a constant shunt-field current of 5.0 A, use MATLAB to plot the motor speed as a function of load. Use the MATLAB "spline ( )" function to represent the magnetization curve of Figure. Neglect armature-reaction effects. Include two plots, one for the case where the series-field ampere-turns add to those of the shunt field and the second for the case where the series-field ampere-turns oppose those of the shunt field.

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Mmf or shunt-field current, per unit 1.4 1.8 0.2 0.4 0.6 0.8 I.0 1.2 1.6 320 1= 0 1.2 300 280 1 = 600 260 1,= 400 1.0 240 = 200 220 0.8 200 180 160 Speed for all curves = 1200 rpm 0.6 140 120 0.4 100 Scale for mmf in A• turns per 80 pole based on 1000 shunt-field turns per pole 60 0.2 40 20 7.0 2.0 3.0 4.0 5.0 6.0 8.0 9.0 0. 1.0 Shunt-field current, A 7,000 8.000 9,000 1,000 2,000 3,000 4,000 5,000 6,000 Mmf, A• turn/pole Generated voltage, V Field-resistance line for Re = 100 2 Field-resistance line for Re 50 2 Generated voltage, per unit