Author: Yau, Wai-tak
Title: Design and development of a disc-type tachogenerator in conjunction with the measurement of the torque/speed characteristics of an induction motor
Degree: M.Sc.
Year: 1996
Subject: Electric motors, Induction
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Pages: vii, 79 leaves : ill. (some col.) ; 30 cm
Language: English
Abstract: In Hong Kong, the torque/speed characteristic of large induction motor cannot be tested by a simple and economic method. This project outlines an effective method to estimate the torque/speed characteristic of an induction motor in a simple and economic way. This method can also be used in measuring torque/speed characteristic of large induction motor which is most popular work-horse in Hong Kong. Basically, the project is sub-divided into two parts. The first part is the main task of the project which deals with development of a disc-type tachogenerator that can be used to trace the torque/speed characteristic of an induction motor. Since this special designed disc-type machine is not available in the market now, it is anticipated that a mass production of the machine will be economical in measuring torque/speed characteristic of induction motor. The second part of the project is to develop a dedicated software program to decode the signals from a brushless synchro resolver which is expensive but is already available in the market. The program is able to measure and plot the torque/speed curve of induction motor using those captured signals. One of the objectives of this project is to compare the results from Parts A and B in terms of cost, efficiency and accuracy, etc. The detailed methodology of both parts are listed below: Part A: This is concerned with the design and manufacture of a disc-type machine that consists of a 3-phase 4-pole stator with a matching rotor. The rotor is fitted with four electromagnets fed with d.c. source via two slip-rings. When used in monitoring the torque/speed characteristics of an induction motor, the disc-type machine is mechanically coupled to the former. As the rotor of the disc-type machine rotates at the same speed of the induction motor being tested, the stator windings of the disc-type machine will induce a voltage which is proportional to common speed of the two machines. The speed dependent output of the machine is fed into an electronic circuit to produce a rippleless d.c. that is proportional to the speed of the induction motor. A suitable differentiator is to be developed to differentiate the speed signal. Since the output torque of the induction motor on no-load is proportional to the time differential of its shaft speed (i.e. T = J帢), the speed differential when obtained, is directly proportional to the output torque of the induction motor. By plotting the speed and the torque signal against each other, the torque/speed characteristics of the induction motor can be obtained. Part B: A brushless synchro resolver is bought from the market that provides a signal corresponding to the position the motor shaft. The output from the resolver is a frequency modulated signal which can also be processed to give an indication of the motor speed. A relatively complicated software is required to decode the signal from the resolver which is, incidentally, very expensive. The cost, efficiency and accuracy of the disc-type machine and the resolver in determining the output torque/speed characteristics of an unloaded induction motor are thoroughly studied in this project.
Rights: All rights reserved
Access: restricted access

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