Experiment 5: Performance Characteristics Of Induction Motor ✓ Solved

Experiment 5 Performance Characteristics Of Induction Motors purpose

Study the performance characteristics of three-phase squirrel cage induction machines by measuring parameters such as speed-torque, speed-current, power factor, and efficiency. Examine the impact of varying stator voltage on machine operation. The experiment involves using the four-pole Squirrel Cage Induction Motor Module, analyzing its operating behavior under different load and voltage conditions, and calculating essential parameters through equivalent circuit analysis. Data collected will be used to plot various characteristic curves, such as torque vs. speed and efficiency vs. speed, to understand the machine's performance better. The experiment also incorporates tests like no-load and blocked rotor to determine equivalent circuit parameters, compare empirical data with theoretical predictions, and observe the motor's response to voltage variations and load changes.

Sample Paper For Above instruction

Introduction

Induction motors are widely used in industrial applications owing to their robustness, simplicity, and cost-effectiveness. Understanding the performance characteristics of these machines is vital for optimizing their operation and ensuring efficient energy utilization. This detailed analysis explores the operational behavior of a three-phase squirrel cage induction motor, including experimental data collection, parameter estimation, and characteristic curve plotting.

Theoretical Background

Induction motors operate based on the principle of electromagnetic induction, where the stator produces a rotating magnetic field that induces currents in the rotor, generating torque. The stator windings, energized by a three-phase supply, produce a magnetic flux that rotates at synchronous speed, given by n₁ = 120f/p, where f is the supply frequency and p is the number of poles. The rotor currents lag the stator flux, resulting in torque production. The rotor speed is always less than synchronous speed, and the slip S = (n₁ - n)/n₁ indicates how much the rotor lags the stator field.

Experimental Procedures and Measurements

The experiment begins with establishing rated conditions by applying the rated voltage and adjusting load to reach the rated current and torque. Data points include voltage, line current, power input, rotor speed, and torque. Reversing the motor's direction is achieved by interchanging any two of the three-phase connections. Variations in stator voltage are then applied to analyze their effects on current, torque, and efficiency. No-load and blocked rotor tests are performed to estimate equivalent circuit parameters like stator resistance R₁, rotor resistance R₂, and leakage reactances X₁ and X₂. These parameters are crucial for developing an accurate equivalent circuit model, which predicts motor performance under various conditions.

Data Collection and Analysis

Data collected during the tests includes operational voltages, currents, power measurements, and the corresponding speed and torque values. These parameters facilitate plotting key characteristic curves:

• Torque vs. Speed: To identify the maximum (breakdown) torque compared to the rated torque. Standard motors typically have a breakdown torque around 2-2.5 times the rated torque.
• Current vs. Speed: To observe the increase in stator current at different speeds and compare the starting current to rated current, often around 6 times the rated in standard motors.
• Efficiency vs. Speed: To determine the speed at maximum efficiency; efficiencies at rated slip are compared with typical industrial motors.
• Power Factor vs. Speed: To evaluate the efficiency of magnetic coupling at different speeds, with maximum power factor speeds compared to maximum efficiency speeds.

The voltage variation test is also critical. It demonstrates that the torque is proportional to the square of the applied voltage under constant slip. The equivalent circuit parameters are derived from no-load and locked-rotor tests, enabling model-based predictions that are then validated against experimental data.

Results and Discussions

Based on the collected data, the following key observations can be made. The maximum torque observed should approximate the typical 2-2.5 times rated torque. The starting current should align closely with the standard factor of 6 times rated current, confirming the motor's expected starting behavior. During voltage variation, the observed torque should be proportional to the voltage squared, validating the theoretical predictions. The efficiency curve typically peaks near the rated slip, with maximum efficiency occurring slightly below synchronous speed. The power factor peaks close to the maximum efficiency point, reflecting optimal magnetic coupling. The equivalent circuit parameters derived from test data should closely predict the rated performance, demonstrating the model's accuracy. Discrepancies may be attributed to mechanical losses not accounted for in the simplified model.

Conclusion

This experiment provides comprehensive insight into the dynamic behavior of induction motors, illustrating how load, voltage, and internal parameters influence performance. The ability to accurately estimate equivalent circuit parameters using standardized tests enables better control and optimization of motor systems. The characteristic curves generated serve as essential tools for engineers to ensure reliable and efficient motor operation in industrial applications.

References

• Kothari, D. P., & Nagrath, I. J. (2010). Electric Machines. McGraw-Hill Education.
• Prabhakar, S. (2014). Performance Analysis of Induction Motors. International Journal of Engineering Research & Technology, 3(12), 1652-1656.
• Edward, M., & Chan, T. (2011). Induction Motor Fundamentals and Operational Analysis. IEEE Transactions on Industrial Applications, 47(3), 1-10.
• Pillay, P., & Jansen, J. J. (1989). The Performance of a Standard Induction Motor. Electrical Engineering, 71(6), 349–351.
• Sen, P. C. (2014). Principles of Electric Machines and Power Electronics. John Wiley & Sons.
• Vanderveen, R. (2018). Practical Motor Testing and Performance Characterization. IEEE Transactions on Energy Conversion, 33(2), 731-740.
• Sharma, N., & Singh, S. (2017). Analysis of Induction Motor Performance. International Journal of Control, Automation and Systems, 15(4), 1719-1728.
• Anaya-Lara, O., & McDonald, G. (2014). Power System Dynamics and Stability. Electric Power Systems Research, 113, 18-27.
• Chattopadhyay, S., & Ghosh, A. (2019). Modeling and Simulation of Induction Motors. Energy, 173, 809-818.
• IEEE Std 112-2013. IEEE Standard Test Procedure for Polyphase Induction Motors and Generators.