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Question: a 1000 kva 4160 v threephase fourpole 60 hz yconnected...

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A 1000 kVA, 4160 V, three-phase, four-pole, 60 Hz, Y-connected synchronous motor has a synchronous reactance of 19.4 Ω and achieves rated open-circuit voltage at a field current of 142 A.  It is operated from a stiff power system which maintains the motor terminal voltage at its rated value.

a.       [2 marks]  At what speed does the motor operate?

b.      [4 marks]  Draw the per-phase equivalent circuit for the motor.

c.       [8 marks]  The motor is initially operating at a load of 500kW with the field current adjusted to achieve unity power factor operation.  Calculate the corresponding field current.

d.      [7 marks]  The load is suddenly increased to 800kW.  Calculate the resultant terminal power factor if the field current remains unchanged from part (c).

e.       [4 marks]  What is the maximum torque the motor can produce if the field current remains unchanged from part (c)?

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