squirrel cage induction motor is the type of electrical machine, which is used to convert electrical energy into mechanical energy. There are no any external electrical connection of rotor it looks like a squirrel cage so it is known as squirrel cage rotor .
squirrel cage induction motor is also known as cage type induction motor.
construction of squirrel cage induction motor
Rotor
semi closed slots are present at outer periphery of the rotor that contain copper bars, we use copper material that enhance the performance of motor because copper has good electrical conductivity . Copper bars connected to heavy end ring . Heavy end ring on both end of the rotor and conductor bars both are eliminated, lamination is the arrangement of various thin strip sheets that joints together.
We provide lamination to reduce eddy current loss. Conductor bars are short-circuited or we can say it completes the circuit with heavy end ring. Heavy end ring is made up of copper or aluminium material. In practical rotor bars, don’t remain in parallel, actually copper bars remain skewed at some angle .
skewing of rotor conductor has many benefits of squirrel cage induction motor
- rotor operates smoothly and provides noise free operation
- uniform torque curve at different positions of the motor
- locking tendency reduces
- length of conductor increases as well as resistance increases
Stator
Stator is the stationary part of squirrel cage induction motor. Stator core is made up of silicon steel to reduce hysteresis loss and core of the stator remain laminated to reduce eddy current loss. And the inner portion of stator or we can say at the inner periphery of the stator slots are present. Where three phase copper winding is placed. Stator winding arranged like that electrically and mechanically 120° apart.
Stator of the motor is made up of silicon steel. Silicon steel has high permeability, so it provide low reluctance path for the magnetic field lines or rotating magnetic field . When we use silicon steel in the machine core, then electrical loss reduces like hysterical loss, what is hysterical loss and eddy current loss I shall write about it in other particular article. Outer frame of the stator is made up of usually cast iron. Frame provides mechanical support to the inner essential components.
working of squirrel cage induction motor
first, we give three phase supply to the stator winding, so due to 3 phase, winding that place 120° apart, rotating magnetic field produces in the air gap of rotor and stater. Rotating magnetic field rotates at synchronous speed that is given by
Ns = 120 F/P
- Ns – synchronous speed
- F – Frequency
- P – Number of poles
when rotating magnetic field cuts the rotor conductor or rotor bars then EMF induces in the rotor conductor from the principle of electromagnetic induction. Since rotor bar is connected to heavy, end ring so rotor bar completes the circuit or we can say rotor bars are short-circuited that create a complete path and due to EMF current starts to flow in the rotor conductor due to that current, another magnetic field set up around the rotor bar and due to interaction between rotating magnetic field and rotor field,
torque acts on the rotor and rotor starts to rotate. In the working of a squirrel gas induction motor, there is no any external electrical connection provided in the rotor. Torque develops on the rotor due to electromagnetism. Thus a squirrel case induction motor operates.
slip in induction motor or squirrel cage induction motor
- slip speed = ( Ns – Nr )
- slip = ( Ns – Nr/Ns )
- percentage slip = ( Ns – Nr/Ns ) 100%
Note :
a squirrel cage induction motor is type of asynchronous motor. It means that this type of motor will not rotate at synchronous speed. speed of rotor will always less than synchronous speed. If rotor speed and synchronous speed will be equal. Then there will know any EMF induced in the rotor conductor and torque will not develop on the rotor. That’s why we designed the motor like rotor speed will be always less than synchronous speed.
on this website, you will get all related topic to the electrical engineering according to the academic syllabus. Right now I am covering electrical machine syllabus. Then after I will cover different other subjects according to the syllabus so this website is very helpful for the students who belongs from electrical engineering and electronics engineering.