Give all your answers correct to 4 d.p. A 470 V permanent-magnet excited DC motor has armature resistance of 1.5 12. When driving a load of constant load torque at rated speed of 1,200 rpm, the armature takes rated 25 A. Speed is controlled by armature voltage variation, and armature is supplied from a three-phase fully controllable bridge rectifier. Available AC voltage is three-phase 400 V, 60 Hz, interfacing transformer is not used, and armature current is continuous. a) The machine operates at rated speed with rated load. Determine rectifier output voltage and thyristor firing angle. [5 marks] Vrect1 = Number V Number o A1 = (degree) b) Determine the rated motor torque and power. [6 marks] Ten = Number Nm Pn = Number kW
c) The machine operates at 40 % of the rated speed with 75 % of the rated load. Determine rectifier output voltage and the thyristor firing angle. [5 marks] Vrect2 = Number V Number A2 = O (degree) d) A three-phase rectifier can operate with different load types at the output. One possibility is placement of a capacitor across the output. Explain when this is done and why? [4 marks] (This question is manually graded.) 1= a= 三三三三三 Equation Editor A A IX BIUS X, X Styles Font Size
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