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%
Advantages
- squirrel case induction motor is available in market at low price, compare to other three phase induction motors.
- since it have not more complicated assembly in the rotor, like slip ring and brushes so requirement of less maintenance.
- squirrel cage induction motor provides good speed regulation.
- it provides high efficiency
- this type of motor provides better heat regulation.
- small and lightweight
- this type of motor is explosion proof
- squirrel case induction motor have relatively constant speed, so it is used for the constant speed operation under varying loads .
- it provides a smooth and quiet operation, due to robust construction and absence of brushes it provides a smooth and quiet operation
Disadvantages
- it have poor speed control compare to slip ringh induction motor
- in starting it, consume more energy
- high starting current and low, starting torque compare to slip ring induction motor
- more copper loss occur in squirrel cage induction motor due to more copper loss, it reduces overall efficiency
- low power factor as compare to slip ring induction motor
Applications
- this type of motor is used in printing machinery
- it is used in conveyor systems , in different industries to drive the conveyor belt, this type of motor is used.
- it is used in different machine tools like lathe machine, milling machines, and other machines tools
- it is used in different machine tools like length machine, milling machine and other machine tools
- this type of motor is used in pumps and fans like centrifugal pumps and large blowers
- it is used in crushers and mixers and in other industrial processing equipment
- this type of motor is also used in the field of agriculture for the application of dairy equipment
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.
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- Squirrel cage induction motor : Video