tailieunhanh - (McGraw-Hill) (Instructors Manual) Electric Machinery Fundamentals 4th Edition Episode 2 Part 8

Tham khảo tài liệu '(mcgraw-hill) (instructors manual) electric machinery fundamentals 4th edition episode 2 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 11 14 03 10 10 AM Page z 7 DC MOTORS AND GENERATORS 627 9-19. A series motor is now constructed from this machine by leaving the shunt field out entirely. Derive the torque-speed characteristic of the resulting motor. 9-20. An automatic starter circuit is to be designed for a shunt motor rated at 15 hp 240 V and 60 A. The armature resistance of the motor is n and the shunt field resistance is 40 n. The motor is to start with no more than 250 percent of its rated armature current and as soon as the current falls to rated value a starting resistor stage is to be cut out. How many stages of starting resistance are needed and how big should each one be 9-21. A 15-hp 230-V 1800 r min shunt dc motor has a full-load armature current of 60 A when operating at rated conditions. The armature resistance of the motor is RA n and the field resistance RF is 80 adjustable resistance in the field circuit Radj may be varied over the range from 0 to 200 ÍÌ and is currently set tQ 90 Ò Armature reaction may be ignored in this machine. The magnetization curve for this motor taken at a speed of1800 r min is given in tabular form below Ea V 150 180 215 226 242 I A a What is the speed of this motor when it is running at the rated conditions specified above b The output power from the motor is hp at rated conditions. What is the output torque of the motor c What are the copper losses and rotational losses in the motor at full load ignore stray losses d What is the efficiency of the motor at full load e If the motor is now unloaded with no changes in terminal voltage or Radj what is the no-load speed of the motor f Suppose that the motor is running at the no-load conditions described in part e. What would happen to the motor if its field circuit were to open Ignoring armature reaction what would the final steady-state speed of the motor be under those conditions g What range of no-load speeds is possible in this motor

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