rotor resistance control lab

Experiment No: …9

PSIM based simulations and analysis of rotor resistance control of three phase wound rotor induction machine. Contents

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Objectives: ............................................................................................................................. ........................2

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Expected outcome of experiment: ..............................................................................................................2

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Theory: ..........................................................................................................................................................2

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Simulation Circuit: ................................................................... ......................................................... ..........3

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Methodology for Measurements: ..............................................................................................................3

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Sample Graphs: ............................................................................................................................. ...............4

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Results and discussion: ...............................................................................................................................4

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Conclusions.....................................................................................................................................................5

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1. Objectives: PSIM based simulations and analysis of rotor resistance control of three phase wound rotor induction machine with i) 25% of rated load ii) 60% of rated load iii) rated load. Discuss the effect of rotor resistance on line current, torque and speed of the machine 2. Expected outcome of experiment: On successful completion of experiment the students will be able to know: 

How to simulate the rotor resistance control in PSim and working of slip ring induction motor.

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About variations in speed and torque of IM by changing rotor resistance in simulation circuit.

3. Theory: In slip ring induction motor, a three phase variable resistor R can be inserted in the rotor circuit. By varying R, the rotor torque can be controlled. The starting torque and starting current can be varied by using rotor circuit resistance. The disadvantage of this method by controlling rotor circuit speed control are:(i) Reduced efficiency at low speed. (ii)Speed changes very widely with load variation. (iii)Unbalance in voltage and current if rotor circuit resistance are not equal. This method of speed control is used when speed drop required for a short time. In overhead cranes, in a load equalization etc. The rotor resistance is varied by three phase rectifier. The three phase rectifier is connected with parallel combination of GTO and resistor R. When the GTO is off the maximum resistance is connected across the rotor circuit. Hence it can be expressed as: Reff = R *(Toff) / T ………………………………….. (1) If k is the duty cycle then: Reff = R *(T-Ton) / T= R(1-k)…………………...….…(2) Where, k= Ton/T

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4. Simulation Circuit:

5. Methodology for Measurements: 1. Connect the circuit as per simulation diagram. 2. By varying the turn off time of GTO, the rotor resistance is increased. 3. Obtain the graphs and waveforms by executing the system

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Sample graphs:

7. Results and Discussion: Based on your measurements, let us now discuss the results that you obtained. Please provide responses to following points:

A. Explain the working of slip ring induction motor? ...................................................................................................................................................... ...................................................................................................................................................... B. Explain the effects of changing duty cycle on the slip ring induction motor? .................................................................................................................................................................... .................................................................................................................................................................... 4

8. Conclusions: Write in your own words the conclusion of performing this experiment. Write about what you learned from this experiment, what you can tell about the rotor resistance control of slip ring induction motor that you did in experiment. .......................................................................................................................................................... .......................................................................................................................................................... ..........................................................................................................................................................

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