Jordan University of Science & Technology

Department of Electrical Engineering

ELECTRICAL MACHINES LAB

EE 336

Experiment # 8

THREE-PHASE INDUCTION MOTOR

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Objectives To determine the equivalent circuit . To measure some characteristics of the 3-phase Induction Motor . Equipments

• Power Pack . • 3-phase squirrel cage Induction Motor ( Dahlander type ). • 3-phase Induction Motor ( slip ring type ) . • Dahlander Switch . • Torque Meter . • Wattmeter . • 4* AVO . • Roter starter .

Procedure Control Unit Setting ; 1. We did the settings as mentioned . NOLOAD TEST : 2. Ip = 1.4 A VL = 380 V PNL = 170 W LOCKED – ROTOR TEST : 3. IBL = 1.97 A VBL = 121 V PBL = 192 w MOTOR CHARACTERISTICS : 4. Ok . 5. & 6. & 7.

No-load A B C D Full-load VL (V) 3 80 380 380 380 380 380 IL (A) 1.4 1.45 1.55 1.67 1.83 2.00

Pin (W ) 170 380 500 660 810 955 N (rpm) 1500 1450 1400 1350 1300 1200 T (N.m) 0 2 3 4 5 6 PO (W) 0 303.66 439.79 565.45 680.63 753.93

η % 0 79.91 87.96 85.67 84.03 78.95

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MOTOR CHARACTERISTICS YY : 8. & 9.

No-load A B C D Full-load VL (V) 380 380 380 380 380 380 IL (A) 1.9 1.92 2.06 2.29 2.6 2.75

Pin (W ) 240 440 740 1040 1300 1400 N (rpm) 3000 2900 2800 2750 2600 2450 T (N.m) 0 1 2 3 4 4.4 PO (W) 0 303.66 586.39 863.87 1089.0 1128.8

η % 0 69.01 79.24 83.06 83.77 80.63 10. Ok . SLIP RING MOTOR CGARACTERISTICS & SPEED CONTROL Speed Control : 11. Ok . 12. VL = 380 V , n = 1500 rpm 13.

Rex 100% 80% 60% 40% 20% 0% n 1250 1300 1350 1400 1450 1500

Motor characteristics : 14. & 15.

Rex = 0 %

No-load A B C D E Full-load VL (V) 380 380 380 380 380 380 380 IL (A) 1.65 1.68 1.73 1.82 1.92 2.08 2.28

Pin (W ) 200 300 420 540 660 820 1000 N (rpm) 1500 1450 1400 1325 1250 1200 1150 T (N.m) 0 1 2 3 4 5 6 PO (W 0 151.83 293.19 416.23 523.56 628.27 722.51 η % 0 50.61 70.00 77.08 79.33 76.62 72.25

16. Rex =30 %

No-load A B C D E Full-load VL (V) 380 380 380 380 380 380 380 IL (A) 1.66 1.68 1.72 1.8 1.92 2.06 2.26

Pin (W ) 180 260 440 540 680 820 980 N (rpm) 1450 1300 1250 1200 1050 950 800 T (N.m) 0 1 2 3 4 5 6

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Graphs : 1. The figures are shown in Fig 1, Fig 2 and Fig 3 . 2. The figures are shown in Fig 4 . 3. The figure is shown in Fig 5 .

Questions :

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3. the speed control method used in the experiment is by connecting an external resistance which called the rotor starter resistance, and by increasing this resistance we found that the speed decrease linearly with it, and this resistance will decrease the amount of the starting current and allow us to control the speed more effectively and it increase the developed torque.

4. synchronous speed : the speed at which the stator rotating field rotates in the air gap . rotor speed : the speed at which the rotor rotates and the induced rotor field rotates in the air gap . slip : the different between the rotor speed n and the synchronous speed . 5. The air gap power is the power across the air gap between the rotor and stator and it includes the developed power and the rotor copper loss , but the developed power is the mechanical

power that results from the motor . 6. Locked-rotor torque : The maximum torque achieved by locking the rotor from moving . Pull-out torque : The maximum torque which motor reach and can’t exceed . Break down torque : The minimum torque at which the motor stop in the motoring domain .

7.Cause there will be no induced voltage and current in the rotor circuit and hence no torque . 8. The wound rotor induction motor is controlled by applying an external resistance and it has a linear

relation with the motor speed ( see Fig 5) but without the existence of this resistance the speed is not easily controlled in both types of motors .

Conclusions :

• When the rotor of an induction motor is looked, the stator current is almost 6 times it rated value . • The speed is not easly controlled , but we can do it by the mean of external resistance . • If the motor speed become greater than the synchronous speed the machine will generate

power(induction generator . • If the motor is running backward with respect to the direction of th e magnetic field, the machine

will stop very rapidly (braking) . • If n = ns , there will be no induced voltage and current in the rotor circuit and hence no torque .

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