1 Electrical Machines EELE 3351 Dr Assad AbuJasser

1 Electrical Machines (EELE 3351) Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

2 Assad Abu-Jasser, Ph. D Electric Power Engineering The Islamic University of Gaza ajasser@iugaza. edu. ps www. site. iugaza. edu/ajasser Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

3 Chapter 7 Induction Motors Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

4 Introduction Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

5 Motor Theory of Operation Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

6 Motor Animation https: //www. youtube. com/watch? v=Lt. Jo. JBUSe 28 Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

7 Induction Motor Construction Squirrel-Cage Wound Rotor Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

8 Basic IM Concepts The Concept of Rotor Slip Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

9 Basic IM Concepts Electrical Frequency on the Rotor Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

10 Example 7. 1 A 208 -V, 10 -hp, 4 -pole, 60 -Hz, Y-connected induction motor has a full-load slip of 5%. (a) what is the synchronous speed of this motor? (b) what is the rotor speed of this motor at rated load? (c) what is the rotor frequency of this motor at rated load? (d) what is the shaft torque of this motor at rated load? Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

11 The Equivalent Circuit of an IM Transformer Model Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

12 The Equivalent Circuit of an IM The Rotor Circuit Model Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

13 The Equivalent Circuit of an IM The Final Equivalent Circuit Rotor Circuit Model Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

14 Power and Torque in IM Losses and Power-Flow Diagram Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

15 Example 7. 2 A 480 -V, 60 -Hz, 50 -hp, three-phase induction motor is drawing 60 A at 0. 85 PF lagging. The stator copper losses are 2 k. W, and the rotor copper losses are 700 W. The friction and windage losses are 600 W, the core losses are 1800 W, and the stray losses are negligible. Find the following quantities: (a) the air-gap power PAG (b) the power converted Pconv (c) the output power Pout (d) the motor efficiency Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

16 Power and Torque in IM Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

17 Separating RCL and Power Converted Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

18 Example 7. 3 A 460 -V, 25 -hp, 60 -Hz, 4 -pole, Y-connected induction motor has the following impedances in ohms per phase referred to the stator circuit: R 1=0. 641 Ω R 2=0. 332 Ω X 1=1. 106 Ω X 2=0. 464 Ω XM=26. 3 Ω The total rotational losses are 1100 W and are assumed to be constant. The core loss is lumped in with the rotational losses. For a rotor slip of 2. 2 percent at the rated voltage and rated frequency, find the motor’s (a) speed, (b) stator current, (c) power factor, (d) Pconv and Pout, (e) induced and load torque, and (f) efficiency Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

19 IM Torque-Speed Characteristics Maximum (Pullout) Torque Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

20 Example 7. 4 A two-pole, 50 -Hz induction motor supplies 15 -k. W to a load at a speed of 2950 rpm. (a) what is the motor’s slip? (b) what is the induced torque in the motor under these conditions? (c) what will the operating speed of the motor be is its torque is doubled? (d) how much power will be supplied by the motor when the torque is doubled? Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)

21 Example 7. 5 A 460 -V, 25 -hp, 60 -Hz, 4 -pole, Y-connected induction motor has the following impedances in ohms per phase referred to the stator circuit: R 1=0. 641 Ω R 2=0. 332 Ω X 1=1. 106 Ω X 2=0. 464 Ω XM=26. 3 Ω (a) What is the maximum torque? At what speed and slip does it occur? (b) what is the starting torque? (c) when the rotor resistance is doubled, what is the speed at which the maximum torque now occurs? What is the new starting torque? (d) calculate and plot the torque-speed characteristics of this motor both with the original rotor resistance and with the rotor resistance doubled. Dr. Assad Abu-Jasser – EE Department - IUGaza Electrical Machines (EELE 3351)