Induction Motor L6 Notes PDF

ECO224 ELECTRICAL MACHINES CHAPTER 4 3 PHASE IM Part 2 Dr. Wael Mamdouh Electrical Engineering Department Egyptian Academy for Engineering and Advanced Technology Equivalent circuit 1- They have not the same 2-...

ECO224 ELECTRICAL MACHINES CHAPTER 4 3 PHASE IM Part 2 Dr. Wael Mamdouh Electrical Engineering Department Egyptian Academy for Engineering and Advanced Technology Equivalent circuit 1- They have not the same 2- They have not the same frequency no. of turns Equivalent circuit Equivalent circuit Equivalent circuit 𝒓ƴ 𝟐 = 𝒓ƴ 𝟐 + 𝑹𝑳 𝑺 Equivalent circuit Power flow Power flow Torque Torque Depends on rotor Depends on  Depends on I2’ speed Torque-Speed (slip) C/Cs Torque-Speed (slip) C/Cs S=1 S = ?? Torque-Speed (slip) C/Cs Torque-Speed (slip) C/Cs  Torque Points Starting torque – Torque at zero speed – Typically 1.5 times the full-load torque Pull-up torque – The minimum torque developed by the motor while accelerating from zero speed – Greater than full-load torque; less than starting torque Breakdown torque – The maximum torque that the motor can develop – Typically 2.5 times the full-load torque Normal operation – At full-load, the motor runs at n rpm – Rotor speed decreases slightly from synchronous speed with increasing load torque – Motor will stall when the load torque exceeds the breakdown torque 4 quadrants torque-speed C/Cs Effect of rotor resistance Starting of induction motor Types of starters 1 Direct Connection 2 Types of starters 3 Auto-Transformer (cont.) Types of starters 4 Star-Delta (cont.) Types of starters 5 Soft-Starter Types of motor loads  Speed Control of IM 𝒏 = 𝒏𝒔 (𝟏 − 𝒔) 1 Change the synchronous speed 2 Change the slip 𝟔𝟎 𝒇 ▪ Change the source voltage 𝒏𝒔 = ▪ Change the rotor resistance 𝑷 ▪ Change the frequency ▪ Change the no. of poles Speed control 1 Speed control 2 Speed control 3 Speed control T Constant Torque Constant Power V V/f = Constant V = Constant f Speed control 4 Pole change method Speed control (Direction) If any two phases for a 3 phase induction motor are interchanged the motor will run in reverse direction Motor Nameplate Squirrel cage vs slip ring Testing of IM Testing of IM