| Abstract: |
This thesis represents a study for the subject of, the characteristics of multi starting operation of unsymmetrical three-winding single-phase induction motors. Theoretical analysis for predicating motor characteristics is developed, and proved to yield good agreement when compared with the experimental characteristics of different industrial motors from the same type. The results achieved can be summarized in the foIlowing points:l.Equations for predicating the performance ofunsymmetrical3-winding I-phase induction motor are derived for different number of turns of the third winding.2.0peration ofunsymmetrical3-winding I-phase induction motor is achieved using one capacitor.7. When the number of turns of the third winding is decreased, the voltage on this winding will be decreased by the same ratio, to prevent increasing the input current value. Consequently the terminal voltage must be decreased. This means that when the number of turns of the third winding change the terminal voltage on the motor will change also and this is not practical, because the terminal voltage is constant (220volt). To overcome this problem the number of turns of all windings will increase by a ratio equal to (220/ variable terminal voltage), hence all the motor parameters will increase by the same ratio square.8. The input current, input power, output power, output torque and efficiency are decreased with decreasing the third winding turns.9. The ratio between the motor starting and fuIl load currents is decreased with decreasing the third winding turns with higher number of poles.10. As the number of poles is increased, the stator resistance will be increased. For the same core dimension, when the number of poles is increased the number of stator turns per phase will be increased. And the cross sectional area of stator conductors will be decreased.11. The rotor resistance will be increased with increasing the number of poles. When the number of poles is increased, the number of parallel paths per pole will be decreased.8. With increasing the number of poles, the number of conductors per slot will be increased. So the motor leakage reactances are increased.9.For the same motor frame, increasing the number of poles does not effect the magnetizing mmf since the flux density remains the same. So the magnetizing reactance may be considered constant.10. With high number of poles the ratio between motor starting and full load current is decreased. Also the input power, output power, output torque and efficiency at rated speed are decreased.11. From studying the effect of changing the third winding turns and the effect of changing the number of poles on the motor characteristics, it is found that there is a particular value of turns ratio (b = 0.5) and number of poles (p = 12) to decrease the ratio between motor starting and full load current. This ratio has a minimum value equal to 1.01 with b = 0.5 and p = 12.12. At low speed the ratio between the total starting losses and the total full load losses is decreased with decreasing the turn’s ratio. The efficiency at full load also decreases.From the results achieved throughout the work of this thesis, the following points can be investigated.1- The research activity must be directed to find a method to improve the efficiency of this kind of motors.2- It is worthwhile to compare the results obtained through the work while the motor is star connected to that would obtained if its stator is delta connected.
|
|
|