Information about INDUCTION MOTOR

Published on October 7, 2012

Author: UpendraKr.



Induction Motors: Induction Motors Presentation By S.R.Paraskar Electrical Dept SSGMCE “AC Motor”: “AC Motor” Electrical Energy Mechanical Energy The purpose of an AC Motor is to Convert Electrical Energy into Mechanical Energy What is AC motor?: What is AC motor? An AC motor is an electric motor that is driven by an alternating current . It has two basic electrical parts: a "stator" and a "rotor" STATOR: STATOR The stator is in the stationary electrical component. It consists of a group of individual electro-magnets arranged in such a way that they form a hollow cylinder, with one pole of each magnet facing toward the center of the group. The term, "stator" is derived from the word stationary. PowerPoint Presentation: The stator has laminated type of construction made up of stampings which are 0.4 to 0.5 mm thick The stampings are slotted on its periphery to carry stator windings Rotor: Rotor The rotor: is the rotating electrical component. It also consists of a group of electro-magnets arranged around a cylinder, with the poles facing toward the stator poles. The term "rotor" is derived from the word rotating. Types of Rotor : Types of Rotor There are two types of motor rotors: 1- The squirrel cage The “Squirrel cage” consists of bars of copper or aluminum electrically connected at each end with conducting rings. The entire structure looks like a cage Wound Rotor: Wound Rotor 2.Slip Ring rotor or wound rotor In This type rotor wdg is similar to stator , wound for same no.of poles as that of stator . Slip rings are available Notice the slip rings How induction motors work : How induction motors work 3 PH supplied to stator Rotating Magnetic field generated that moves around rotor Ns=120f/p PowerPoint Presentation: Stationary rotor conductors cuts rotating magnetic field and emf is induced in conductor Rotor is shtckt it circulates a current. It becomes current carrying conductor placed in magnetic field Rotor starts rotating in same direction of rotating magnetic field Why the rotor rotates in same direction of magnetic field: Why the rotor rotates in same direction of magnetic field Acc to Lenz law “The net effect opposes its cause” here the net effect is production of current and cause is EMF There exist a relative speed between stationary conductor and rotating magnetic field To oppose this cause stationary conductors starts rotating in same direction as that of rotating magnetic field Induction motor speed: Induction motor speed At what speed will the IM run? Can the IM run at the synchronous speed, why ? If rotor runs at the synchronous speed, which is the same speed of the rotating magnetic field Then the rotor will appear stationary to the rotating magnetic field and the rotating magnetic field will not cut the rotor. PowerPoint Presentation: So, no induced current will flow in the rotor and no rotor magnetic flux will be produced so no torque is generated. If the rotor speed will fall below the synchronous speed When the speed falls, the rotating magnetic field will cut the rotor windings and a torque is produced Concept of Slip: Concept of Slip Stator Flux Rotor Slip In practice the IM will always run at a speed lower than the synchronous speed The difference between the motor speed and the synchronous speed is called the Slip PowerPoint Presentation: Slip of IM is given by Ns is Synchronous speed (speed of rotating magnetic field ) N is speed of Rotor Percentage slip given by PowerPoint Presentation: Speed of motor N= Ns(1-S) When rotor is stationary i.e N=0 Slip=1 or 100% In IM the change in speed from no load to full to full load is hardly 1% to 3% So essentially it is constant speed motor Induction Motors and Transformers: Induction Motors and Transformers Both IM and transformer works on the principle of induced voltage Transformer: voltage applied to the primary windings produce an induced voltage in the secondary windings Induction motor: voltage applied to the stator windings produce an induced voltage in the rotor windings PowerPoint Presentation: The difference is that, in the case of the induction motor, the secondary windings can move Due to the rotation of the rotor (the secondary winding of the IM), the induced voltage in it does not have the same frequency of the stator (the primary) voltage Frequency of Rotor current: Frequency of Rotor current At standstill the frequency of the rotor current is same as the supply freq But when rotor starts rotating the frequency depends upon the relative speed or slip speed f’=S X f Where f’ is freq of rotor current S is slip and f is supply freq Thank you: Thank you

Related presentations