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In later years, motors improved and could be run directly from a 60 Hz power supply. As a result, 25 Hz power systems shrank and disappeared. However, there were many perfectly good working 25 Hz motors in factories around the country that owners were not ready to discard. To keep them running, some users created their own 25 Hz power in the plant using motor-generator sets. A motor-generator set consists of two machines connected on a common shaft, one acting as a motor and the other acting as a generator. If the two machines have different numbers of poles but exactly the same shaft speed, then the electrical frequency of the two machines will be different due to Equation (3-34). What combination of poles on the two machines could convert 60 Hz power to 25 Hz power?
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Chapter 3 Solutions
Electric machinery fundamentals
- The armature of a shunt generator has 0.08-ohm effective resistance. Each brush has an effective resistance of 0.02 ohm. The terminal voltage is 120 V while the current is 60 A. What is its efficiency?arrow_forwardAppliances in home that use DC motor and briefly explain why it works as reverse DC generatorarrow_forwardA field excitation of 20 A in a certain alternator results in an armature current of 400 A in short circuit and a terminal voltage of 2000 V on open circuit. The magnitude of the internal voltage drop within the machine at a load current of 200 A isarrow_forward
- The DC shunt generator with the terminal voltage 325 V, armature drop 9 V and the each brush drop 4 V, then the value of generated emf is narrow_forwardThe rotor of a 220 –V 60 Hz, 4-pole induction motor has a power input of 80kW is observed that the rotor emf makes 90 cycles per minute. Calculate the rotor copper loss. (a). 2kW (b). 5kW (c). 3kW (d). 4kWarrow_forward3 phase motors are widely used in the industry. they require little maintenance, having no brush gear or centrifugal switch, are robust and relatively inexpensive.arrow_forward
- An alternator has a poles a) At what speed must the machine be driven to develop 60 cycles? 25cycles? What frequency is developed if the speed is 1,000 rpm?arrow_forwardthe field windings of a series motor has a resistance of 120 ohms at 15° c. after running for 2 hours, the resistance has increases to 140 ohms. if the temperature coefficient of the windings at 0°C is 0.004, find the new temperature of the windingsarrow_forwardWhat conditions must be met before two alternators can be paralleled together?arrow_forward
- The DC shunt generator with the terminal voltage 325 V, armature drop 9 V and the each brush drop 4 V, then the value of generated emf isarrow_forwardThe maximum speed of an alternator working at 60 Hz is possible when the number of poles of the machine is **.***LEE a. 2 b.4 C. 5 d. 3 The cerrecttanswer is 2arrow_forwardO c. K = 101.86 and flux =3.33 mWb / pole O d. K = 59.5 and flux = 1.33 mWb/pole In a given DC motor, the output power is 45 HP, and the copper losses are 2.005 KW. If the rotational losses is one tenth of the output power, find the converted power and the efficiency of the motor. Select one: O a. None O b. Prony = 33.57 KW and % efficiency 89.2 % O c. Pcony = 39 KW and % efficiency 75.8 % O d. Pcony = 36.927 KW and % efficiency 86.2 % Ps Ae Pr Aiarrow_forward
- Electricity for Refrigeration, Heating, and Air C...Mechanical EngineeringISBN:9781337399128Author:Russell E. SmithPublisher:Cengage LearningDelmar's Standard Textbook Of ElectricityElectrical EngineeringISBN:9781337900348Author:Stephen L. HermanPublisher:Cengage Learning
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