2. A 250 kVA, 480 V, 50 Hz, delta-connected alternator with a rated field current of 5 A was tested and the following test data were obtained: • Open circuit terminal voltage from OC test data is 540 V at the rated IF. Short circuit current from SC test data is 300 A at the rated If. •A dc current of 20A is flowing through any two stator armature terminals, when a DC voltage of 10 V was applied to two of the terminals. Evaluate the following from above tests data the armature resistance, the approximate synchronous reactance and voltage regulation at rated load and 0.7 pf lead.

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Problem # 1: A four-pole DC machine has a wave winding of 300 turns. The flux per pole is 0.025 Wb. The DC machine rotates at 1000 rpm. a) Determine the machine constant, b) Determine the generated voltage, c) Determine the kW rating if the rated current through the turn is 25 A. Problem # 2: The following information is taken from the nameplate of a separately-excited dc generator. Armature: 120 kW, 600 V, 0.15 Q. Field: 100 V, 6.0 A At its rated speed of 3600 rpm the no-load torque is measured at 16 Nm. Ignore armature reaction and magnetic saturation. a) For rated load conditions determine: i) Rated Shaft Horsepower ii) Rated Efficiency iii) Load Impedance b) Determine the terminal voltage, kW output and the efficiency if the field current is reduced to 4.5 A, and the speed is reduced to 3000 rpm, causing the rotational losses to become 4 kW. The load impedance is unchanged.

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