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Explain series switching control of AC load.

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A 750 Hp, 250 V, 1200 r/min DC motor is connected to a 208 V, 3 phase, 60 Hz, line using a 3 phase bridge converter. The full load armature current is 2500 A and the armature resistance is 4 m ohm. Calculate the required firing angle under rated full load conditions. 

(A) 45 deg (B) 208 deg (C) 27 deg (D) 32 deg 

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