The document discusses the double cage induction motor. It has two rotor windings or cages that provide high starting torque at low starting current. The rotor has an outer winding made of manganese bars with small cross-section and high resistance. It also has an inner winding made of copper bars with larger cross-section and lower resistance. This arrangement allows the motor to produce high starting torque while limiting starting current draw. The double cage induction motor provides benefits like high efficiency, good speed regulation, lower costs, and increased robustness over traditional squirrel cage motors.

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. Overview
• Introduction
• Benefits
• Why we use it
• Construction
• Working

4. Why we need it..
• 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.
i. Wound rotor
ii. 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.

7. Construction Of DSC Motor
• 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

8. The Outer winding
• 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

9. The Inner Winding
• 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.

12. Advantages
• 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.

13. 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.

14. 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.

15. Working….