Why does a double cage rotor motor have good efficiency under normal operating conditions?
The impedances of all the layers are nearly equal, so current flows through all the parts of the bar equally. The resulting large cross-section area makes rotor resistance small, resulting in good efficiency at low slips.
What is the advantage of double squirrel cage rotor as compared to the round bar cage rotor?
A double cage rotor has low starting current and high starting torque, therefore, it is more suitable for direct on line starting. Since effective rotor resistance of double cage motor is higher, there is larger rotor heating at the time of starting as compared to that of single cage rotor.
What is the advantage of double squirrel cage induction motor?
The advantage of a double-squirrel cage motor is that it provides high starting torque and low starting current.
Why the starting torque of squirrel cage induction motor is low?
It suffers from the disadvantage of a low starting torque. It is because the rotor bars are permanently short-circuited and it is not possible to add any external resistance to the rotor circuit to have a large starting torque.
Why is the efficiency of an induction motor so poor at high slips?
When an induction motor is started, the slip value is equal to 1 since the rotor is not moving. Therefore, the induced magnetic field and current in the rotor can be very large. This in turn causes a high current to be drawn by the stator that can cause damage to the motor if not controlled.
What will happen if air gap is increased in an induction motor?
The permeability of the magnetic circuit will decrease if the air gap of the motor is increased. The magnetizing inductance of the motor decreases. … The air gap will have a decrease in magnetic flux.
Why is the speed of the squirrel cage motor fixed?
‘Fixed’ speed induction generators
Because the speed variation from no load to full load is very small, the term ‘fixed’ speed tends to be widely used. … The design and construction of the stator and rotor of an induction generator are similar to that of a large induction motor having a squirrel-cage rotor.