Ee22 Problem Set 1

Problem Set 1:

1. Two 500-kW, 250-V, under-compound generators A and B are operating in parallel. The voltage regulation of machines A and B are 2 and 3 percent, respectively. Both machines are operating at rated load and 250 V. Determine (a) the new bus voltage and (b) the division of load between machines when the total bus load drops to 2800 A. 2. A short-shunt compound generator has a shunt-field resistance of 77 ohms, a series-field resistance of 0.008 ohm, a commutating-pole winding resistance of 0.005 ohm, and an armature resistance, including brushes, of 0.02 ohm. When the armature current is 128 A, the generated emf is 234.2 volts. Calculate the power delivered to the load. 3. The armature of a dc motor has 31 slots with 16 conductors in each slot. Only 68 percent of the conductors lied directly under the poles faces, where the flux density is uniform at 46,000 lines per square inch. If the armature-core diameter is 7.25 inches, its length 4.25 inches, and the current in each conductor is 25 amperes, calculate: (a) the force exerted by the armature tending to produce rotation; (b) the torque in pound-feet. (25 points) 4. A four-pole machine generates 250 volts when operated at 1,350 rpm. If the flux per pole is 1.85 x 10 6maxwells, the number of armature slots is 45, and the armature winding has two parallel paths, calculate (a) the total number of armature conductors; (b) the number of conductors in each slot. (25 points) 5. Two DC generators are operating in parallel and take equal shares of a 900kW bus load at 555 V. Generator A is rated at 500 kW, 600 V, and 3 percent regulation. Generator B is rated at 750 kW, 600 V, and 5 percent regulation. If the bus load drops to 1000 A, determine (a) new bus voltage; (b) current supplied by each machine. 6. A 5-kW 120-volt compound generator has an armature resistance of 0.23 ohm, a series-field resistance of 0.04 ohm, and a shunt-field resistance of 57.5 ohms. Assuming a long-shunt connection and a voltage drop at the brushes of 2 volts, calculate the generated emf at full load.

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