A machine that converts electric ennergy into mechanical energy is called electric motor. These are simple in design, easily used, low cost, high efficiency, low maintenance, and reliable. Three-phase induction motors are one of the types and different from other types of electric motors. The main difference is that there is no electrical connection from the rotor winding to any source of supply. The required current and voltage in the rotor circuit are provided by induction from the stator winding. This is the reason to call is as an induction motor. This article describes the Squirrel cage induction motor, which is one of the types of three-phase induction motor.
What is Squirrel Cage Induction Motor?
Definition: Squirrel cage motor is one of the types of induction motors. In order to generate motion, it hardens electromagnetism. As the output shaft is connected to the rotor inner component which is looking like a cage. Hence it is called squirrel cage. The two-end caps i.e, circular in shape are joined by rotor bars. These are acted based on the EMF i.e, generated by the stator. This EMF is also generated outer housing that is made of laminated metal sheets and wire coiling. The two main parts of any type of induction motor are the stator and the rotor. The squirrel cage is a simple method of pulling an electromagnetic induction effect. A 4-pole squirrel cage induction motor is shown below.
Squirrel Cage Induction Motor Working Principle
Squirrel induction motor working is based on the principle of electromagnetism. When the stator winding is supplied with a thee-phase AC, it produces a rotating magnetic field (RMF) which has a speed called synchronous speed. This RMF causes voltage induced in the rotor bars. So, that current flows through that. Due to these rotor currents, a self magnetic field is generated which interacts with the stator field. Now, as per the principle, the rotor field starts opposing its cause. when the RMF catches the rotor moment, the rotor current drops to zero. Then there would be no relative moment between the rotor and RMF.
Hence, the zero tangential force is experienced by the rotor and reduces for a moment. After this reduction in the moment of the rotor, the rotor current is induced again by the reconstruction of relative motion between the RMF and the rotor. Hence the tangential force of the rotor for the rotation is restored and starts by following the RMF. In this case, the rotor maintains a constant speed, which is less than the speed of RMF and synchronous speed. Here, the difference between the speed of RMF and the rotor is measured in the form of slip. The final frequency of the rotor can be obtained by the multiplication of slip and supply frequency.
Squirrel Cage Induction Motor Construction
Parts that are required for the construction of squirrel cage induction motor are stator, rotor, fan, bearings. The stator consists of mechanically and electrically 120 degrees apart three-phase winding with metal housing and core. In order to provide the path of low reluctance for flux generated by AC current, the winding is mounted on the laminated iron core.
Rotor converts given electrical energy into mechanical output. The shaft, a core, short-circuited copper bars are the parts of the rotor. In order to avoid hysteresis and eddy currents that are leading to power loss, the rotor is laminated. And I order to prevent cogging, conductors are skewed which also helps to give a good transformation ratio.
A fan attached at the back of the rotor for heat exchange helps in maintaining under a limit of the temperature of the motor. For the smooth rotation, bearings are provided in the motor.
Difference between Squirrel Cage Induction Motor and Slip Ring Induction Motors.
Advantages
The advantages of a squirrel cage induction motor include the following
Simple and rugged construction.
The low initial as well as maintenance cost.
Maintains constant speed.
The overload capacity is high.
Simple starting arrangement.
High power factor.
Low rotor copper loss.
High efficiency.
Disadvantages
The disadvantages of a squirrel cage induction motor include the following.
Motor
High starting current
Very sensitive to fluctuations in supply voltage
Low power factor at light loads.
Speed control is very difficult
Very poor starting torque due to its low rotor resistance.
Post time: Jun-26-2024
