Question

2.3 (20 points) A separately-excited de motor is mechanically coupled to a three-phase, 4-pole, 30-kVA, 460-V, round-rotor synchronous generator. The de motor is connected to a constant 230-V de supply The ac generator is connected to a 460 V, fixed-voltage, fixed-frequency, three-phase supply. The synchronous reactance of the synchronous generator is 513 Ω/phase. The armature resistance of the de motor is 30 m2. The 4-pole de machine is rated 30 kW at 230 V. All unspecified losses are to be neglected. If the set absorbs power from the de source and delivers power to the ac supply a) What is the internal voltage of the ac machine in volts per phase when it delivers 30 kW at unity power factor? b) What is the internal voltage of the de motor? Hint: 30 kW will be delivered by the de motor. This power is the de motor input power subtracted by the armature resistance power consump- tion. c)True or false? At zero power transfer, the two machines will stall and eventually d) At zero power transfer condition, what is the difference between the synchronous machine's in- e) The synchronous generator's field current is kept intact, what adjustment on the de machine can not rotating ternal voltage angle and the ac supply voltage angle? be made to reduce the power transfer between the two machines to zero? Note the de supply and ac supply cannot be changed. Hint: Please think what variables can be controlled by a de machine besides the de armature terminal voltage.

Answer 1

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