SPEED TORQUE CHARACTERSTICS OF 3 PHASE INDUCTION MOTOR BY GYAN VARDHAN TYAGI DHEERAJ SHARMA

Three Phase Induction Motor

Based on the construction of the rotor, a 3-phase induction motor can be categorized into two types: i. Squirrel Cage Induction Motor ii. Wound Rotor or Slip Ring Induction Motor In squirrel cage IM, the rotor consists of longitudinal conductor bars which are shorted at ends by circular conducting rings. Whereas, the wound rotor IM has a three phase balanced distributed winding even on the rotor side with as many number of poles as in the stator winding The stator of both types of motors consists of a three phase balanced distributed winding with each phase mechanically separated in space by 120 degrees from the other two phase windings. This gives rise to a rotating magnetic field when current flows through the stator

The per phase equivalent circuit of an induction motor is shown below:

IM -Induction Motor Rs -Stator Resistance Rr -Rotor Resistance Rr’ -Rotor Resistance Referred to Stator side Xs -Stator Reactance Xr -Rotor Reactance Xr’ -Rotor Reactance Referred to Stator side Xm -Leakage Inductance I1 -Stator Current I2 -Rotor Current I2’ -Rotor Current Referred to Stator side Im -Magnetizing Current V0 -Stator Voltage s -Slip ωs- Synchronous Speed ωm- Rotor Speed (Machine Speed) Ωs -Average Synchronous Speed (in RPM) f -Supply Frequency p -No. of Poles Pg- Air-gap Power Pcu- Copper loss in the machine Pm -Mechanical Power output of the machine T -Torque Developed by the motor sm- Slip at maximum torque

Tmax- Maximum Torque ωsl- Slip Speed ωf -Rotor Speed at Frequency f

CALCULATION OF TORQUE s = (ω s – ωm)/ ω s ω s = 120f/p rpm

Power transferred to rotor (or air-gap power) Pg=3I2R/s Rotor current I2=V0/{(Rs+Rr/s)+j(Xs+Xr)} Power transferred to rotor (or air-gap power) Pg=3I2R/s Rotor copper loss is Pcu=3I2Rr

Electrical power converted into mechanical power Pm=Pg-Pcu=3I22Rr{(1-s)/s} Torque developed by motor T=Pm/ ωm Thus, T= 3I22Rr/s ω s

SIMULATION MODEL

RESULTS ROTOR CURRENT

SPEED OF ROTOR

STATOR CURRENT

ELECTROMAGNETIC TORQUE

SPEED TORQUE CHARACTERSTICS