Double Cage Induction motor

University Of Gujrat(Department of electrical engineering)

1. Zia Mohi U Din 15103122-016 Junaid Ahmed 15103122-023 Waqas Ahmed 15103122-025 University Of Gujrat (DOET) Group Members

2. Double Cage Induction motor

3. Introduction Benefits Why we use it Construction Working

4. Conventional squirrel cage motors suffer from low starting torque and High strarting Current. It has a double cage or     two Rotor windings  or cages are used. This arrangement is used for obtaining high starting torque at a low value of starting current. The stator of a double cage rotor of an induction motor is same as that of a normal induction motor . In the double cage rotor of an induction motor there are two layers of the bars.

5. Introduction Induction motor has two types on basis of construction. Wound rotor Squirrel cage rotor In wound rotor we limit current by using external resistances through slip rings. But squirrel rotor is short circuited so cannot add resistance to it.

6. Rotor of this motor has two squirrel-cage windings located one above the other. The rotor has two main parts ( i ) The outer winding ( ii) The inner winding

7. Outer layer has the bars of small cross sections. Usually made of manganese This outer winding has relatively large resistance . The bars are shorted at the both ends . The flux linkage is thus very less .   Double squirrel-cage rotor bars

8. Inner layer bars has greater cross sectional area than that of outer winding in order to have resistance one fourth or one fifth of outer winding. Usually made of Red copper. End rings may be separate or combined.

9. It has high efficiency and good speed regulation. It gives higher starting torque. Lower starting current and are cheaper in cost. They are more robust and are explosion proof since the risk of sparking is eliminated by the absence of slip ring and brushes.

10. Double Squirrel-Cage Rotor Working At starting, the rotor frequency is the same as that of the line (i.e., 50 Hz ),making the reactance of the lower winding much higher than that of the upper winding.

11. At Running Condition… As the motor accelerates, the rotor frequency decreases, thereby lowering the reactance of the inner winding, allowing it to carry a larger proportion of the total rotor current.

12. Working….