DC Generators

Problem 479: The armature of a four-pole shunt generator is lap wound and generates 216 volts when running at 600 rpm. The armature has 144 slots, with six conductors per slot. If this armature is rewound, wave connected, find the emf generated at the same speed and flux per pole.

Problem 480: A two-pole DC generator has an armature containing a total of 40 conductors connected in two parallel paths. The flux per pole is \(6.48\times10^8\) lines and the speed of the prime mover is 30 rpm. The resistance of each conductor is 0.01 ohm and the current carrying capacity of each conductor is 10 A. Calculate the terminal voltage of the generator.

Problem 481: A four-pole DC generator has an armature winding containing a total of 648 conductors connected in two parallel paths. If the flux per pole is \(0.321\times10^6\) maxwells and the speed of rotation of the armature is 1,800 rpm. Calculate the ampacity required in each armature conductor if the power developed by the armature is 5 kW.

Problem 482: A 4-pole DC generator with duplex lap winding has 48 slots and four elements per slot. The flux per pole is \(2.5\times10^6\) maxwells and it runs at 1500 rpm. What is the output voltage?

Problem 484: A four-pole shunt connected generator has a lap connected armature with 728 conductors. The flux per pole is 25 mWb. If the generator supplies two hundred fifty 110 V, 75 W incandescent lamp. The field and armature resistances are 110 ohms and 0.025 ohm respectively. Determine the speed in rpm of the generator.

Problem 485: A speed-indicating device consists of a 2-pole permanent magnet DC generator with a 2000-ohms DC voltmeter connected across its terminals. The generator has an armature with 1200 conductors having two parallel paths and a total resistance of 1000 ohms between brushes. The air gap flux is 40,000 lines per pole. If the voltmeter reads 10 V, at what speed will this reading indicates?

Problem 486: A shunt generator supplies a load of 5,500 W at 110 V through a pair of feeder conductors having a resistance of 0.02 ohm each. The armature, shunt field resistances are 0.15 ohm and 50 ohms respectively. Find the emf generated.

Problem 487: The no-load voltage of a 50-kW, 220 volts, shunt generator in the FEU laboratory is 232 volts and rated load voltage is 220 volts. The armature resistance including brushes, is 0.026 ohm and the resistance of the shunt field resistance is 52 ohms. What is the induced electromagnetic force at rated load?

Problem 488: The field current of a 180 kW, 250 volts DC shunt generator is 6 A when running full load at rated terminal voltage. If the combined armature and brush resistance is 0.02 ohm, solve for the electrical efficiency of the generator.

Problem 489: The field circuit of a 200,000 watts, 230-V shunt generator is 8 A when running full load at rated terminal voltage. If the combined brush and armature resistance is 0.03 ohm, solve for the electrical efficiency of the generator.

Problem 491: The armature of a shunt generator has 0.05 ohm effective resistance. Each brush has an effective resistance of 0.01 ohm. The terminal voltage is 100 volts while the current is 40 amperes. What is its efficiency?

Problem 493: A 15 kW, 230 V, shunt generator was run light as a motor to determine its stray power losses at rated load. The applied voltage across the armature, computed for test was 254 V and the armature current drawn is 2 A. The armature and shunt field resistances are 0.25 and 100 \(\Omega\), respectively. Calculate the generator efficiency at half load. Assume stray power losses to be constant.

Problem 494: A shunt generator supplies 100 A at 200 V. The armature and shunt resistances are 0.025 \(\Omega\) and 100 \(\Omega\), respectively. If the copper losses are equal to the iron losses at this load, find the brake horsepower of the engine driving the generator.

Problem 495: A 20 kW, 200 V shunt generator is operated at rated load. If the driving engine is developing 30 bhp, determine the iron and friction losses. Armature resistance is 0.05 ohm and shunt field resistance is 50 ohms.

Problem 496: A 220 V shunt generator has an armature resistance of 0.02 \(\Omega\) and a shunt resistance of 44 \(\Omega\). At rated load, the driving engine develops 62.25 hp. If the iron and friction losses amount to 1600 W, how much is the current delivered to the load at rated condition?

Problem 497: A DC generator has no-load output voltage of 120 volts. Its armature circuit resistance is 0.95 ohm and its field coils are separately energized. If the load is rated 2 kW at 115 V. Neglecting the effect of armature reaction, what power could be delivered to the load?

Problem 498: The armature of a 6-pole separately excited dc generator is lap wound with 534 conductors. This machine delivers power to the load at 250 V while being driven at 1000 rpm. At this load, the armature circuit dissipates 640 W. If the flux per pole of this generator is 30-mWb, determine the kW rating of the load served. Assume a total brush contact drop of 2 V.

Problem 499: A separately excited generator when running at 1200 rpm supplies 200 A at 125 V to a circuit of constant resistance. Armature circuit resistance is 0.10 ohm. Determine the terminal voltage when the speed is dropped to 1000 rpm? Assume that the field current is unaltered.

Problem 500: A dc series generator is supplying a current of 5 A to a series lighting system through a feeder of total resistance, 1.0 ohm. The terminal voltage is 2500 V. The armature and series field resistances are respectively 18 and 15 ohms respectively. A 30-ohm diverter resistance is shunted across the series field. Determine the power developed in the armature of the generator?

Problem 502: The hysteresis and eddy current losses of a DC machine running at 1000 rpm are 250 watts and 100 watts, respectively. If the flux remains constant, at what speed will the total iron loss be halved?