A New winding design in phase modulation technique for pole-chaning of threephase induction motors

Three-phase induction motors are alternating current machines and they are widely used in industry because of their certain ad vantages, unlike the d-c motors, they have a constant speed, that is, their speed can not be changed continuously in an economical way. The most economic speed change in three-phase induction motor is obtained by changing the number of poles of the stator winding. In general, pole-amplitude modulation or phase modulation techniques are applied for changing the number of poles by using a single winding in three-phase squirrel-cage induction motors. Recent studies are focusing on pole-amplitude modulation technique, because this technique is more economic than phase modulation technique from the point of view of the number of leads and of switching processes. -iii-The appearance of a large number of leads in phase modulation technique plays a discouraging role in using this winding technique. In this thesis the phase modulation technique has been realised with six leads of the winding by using a new winding connection. Altnough the same thing is valid also for pole^amplitude modulation technique, the switching process in the new winding connection of the phase mo dulation technique is more simpler. In the new winding connection of the phase modulation technique, the winding is separated into three components. Each component is sub divided into three parts individually and then phase connections are made in a convenient way. So, three parallel paths occur in both pole numbers. To obtain parallel paths one of the methods, namely "the met hod of three-steps" or "slot-^star diagrams" is used. The new winding connection is successf ull constant-torque or constant-power requ irements of the motor in close^ratio speed changes. The phase modulation technique using the new winding connection has been tested on three different motors. The experimental results confirmed theoretical calculations. This study, when compaired with similar studies and motors in use, has shown that it can be used successfully in 36 slots induction motors which are widely employed in industy today. Especially in the case of a large number of slots, the new winding connection provides a precise application.