Assignment: Powerlab 3-Phase Induction Motor Performance

En0567 Assignmentc003 Powerlab 3 Phase Induction Motor Performanc

Determine the parameters used to measure squirrel-cage induction motor performance. Plot and understand the typical steady-state operating characteristics of small induction motors. Before you start this assignment you should have a clear understanding of voltage and current in 3 phase AC circuits and be familiar with the use of the 68-500 Virtual Instrumentation System and the connections required to the dynamometer. For details on the connections between the PC, the 68-441 Torque/Speed control panel and the 68-500 Multi-Channel Input/Output panel, see the Manual Multi-Channel Input / Output System – 68-500. Also refer to the Virtual Instrumentation software 68-911 manual.

Perform steady-state measurements of the induction motor with Y and ΄ connections on the stator windings, and compare the operating characteristics under different load conditions. Use the provided formulas to calculate input power, output power, and efficiency. Equipment required includes a universal power supply, a three-phase squirrel cage induction motor, a dynamometer system, shaft coupling, system frame, bin, patch leads, and a PC with 68-911 software. Follow proper circuit wiring diagrams and safety procedures during setup and testing.

Ensure correct initial setup, including turning off power before connecting equipment, setting the power supply to 0%, and configuring the virtual instrumentation software. During testing, gradually increase the supply voltage to approximately 415 V for Y-connection and 240 V for ΄-connection. Record measurements such as line current, power, power factor, torque, rotational speed, and slip at various load levels. Reconfigure the motor to ΄ connection and repeat measurements for comparison.

Analyze the data to determine the motor's synchronous speed and number of poles, calculate slip, and plot torque versus speed, current, power factor, input power, and slip for both connection types. Use spreadsheet software to create comparative graphs of these parameters to visualize the operating characteristics of the motor. Additionally, explore the proportionality of electromagnetic torque to slip in the low-slip region using the equivalent circuit model, confirming this through experimental data.

Further, explain the operation of the two-wattmeter method for measuring three-phase power, using phasor diagrams and theoretical principles. Discuss the advantages of power electronic starters over electro-mechanical starters for motor start-up, especially for larger machines, and analyze the issue of high starting current and torque in fixed frequency operation. Lastly, determine the maximum safe voltage for ΄-connection to prevent overcurrent and compare performance parameters for different winding configurations.

Paper For Above instruction

The performance evaluation of three-phase squirrel-cage induction motors is fundamental in understanding their operational characteristics, efficiency, and application suitability in industrial settings. These motors are prevalent due to their robustness, simplicity, and self-starting capabilities, making them prominent in various industries, including manufacturing, HVAC, and renewable energy sectors such as wind turbines. This paper discusses the key parameters used to assess their performance, experimental procedures for measurement, theoretical foundations, and the practical implications of winding configurations and starting techniques.

Parameters for Measuring Induction Motor Performance

Measurement of an induction motor's performance typically involves parameters such as input power, output power, torque, efficiency, slip, and the motor's operating speed. The input power (Pin) is determined using the three-phase power formula:

Pin = √3 × V × I × cos φ,

where V is the line-to-line voltage, I is the line current, and cos φ is the power factor (Equation 1). Accurate measurement of these parameters is critical because they directly influence the calculation of efficiency and operational analysis.

The output power, which represents the mechanical power delivered to the load, is calculated as:

Pout = 2π × n × T / 60,

with n being the rotor speed (rev/min) and T the torque (Nm) (Equation 2). Efficiency is then derived by comparing the output and input power:

Efficiency = (Pout / Pin) × 100% (Equation 3).

Additionally, slip, a measure of rotor speed deviation from synchronous speed, is vital when analyzing motor performance, especially in load-dependent conditions. It is expressed as:

s = (Ns - Nr) / Ns,

where Ns is synchronous speed, and Nr is rotor speed.

Experimental Procedures and Setup

The experimental setup involves connecting the motor in both Y and ΄ configurations, ensuring proper wiring and safety measures. Using the virtual instrumentation system, measurements are taken at various load levels, while the motor operates at approximately 415 V and 240 V respectively. The data collected include line currents, input power, power factors, torque, and rotational speeds. These measurements facilitate plotting the performance characteristics such as torque-speed curves, current versus torque, and power factor variation with load.

The process involves starting the motor with no load, gradually increasing load torque, and recording corresponding parameters until reaching the rated load. Repeating the procedure for the ΄ connection allows comparison of the motor's behavior under different winding configurations. The recorded data enable the analysis of steady-state operation, efficiency, and losses.

Theoretical Analysis and Performance Characteristics

The linear relationship between electromagnetic torque and slip in the low slip region is explained by the approximate equivalent circuit of the induction motor. Under small slip conditions, the torque T is proportional to slip s, as evidenced by:

T ∝ s / R2,

where R2 is the rotor resistance. Graphical plots of torque versus slip, obtained experimentally, serve to verify this proportionality. The analysis confirms the motor’s ability to maintain torque characteristics within specified slip ranges, essential for stable operation and control.

The operation of the two-wattmeter method for three-phase power measurement leverages phasor diagrams to demonstrate how the combined readings accurately represent the total apparent power. Each wattmeter measures power on a specific phase and its complement, with the sum or difference providing the total active power depending on the power factor angle. This method's advantage is its ability to measure power accurately even with unbalanced loads or phase shifts, making it versatile in practical conditions.

Advantages of Modern Starting Techniques and Configuration Considerations

Traditional direct-on-line starting results in high inrush currents and torque, risking thermal and mechanical stress, especially in larger machines. Variable voltage starting, such as star-delta or soft starters, mitigates these effects by controlling initial voltage and current to reduce stress during startup. Power electronic starters, including electronic soft starters and variable frequency drives (VFDs), offer additional benefits such as precise speed control, soft start capability, and reduced mechanical wear. Their main advantage over electro-mechanical starters is the ability to adjust motor parameters dynamically, leading to energy savings and better process control.

Dealing with fixed frequency operation, a common challenge is high inrush current during startup and potential torque overshoot. To prevent overloading in ΄ connection, the maximum voltage applied is limited to the reduced line-to-line voltage, approximately 69% of the rated voltage, ensuring the current stays within safe limits. Performance parameters such as current and torque divergences between winding configurations are significant because they influence motor selection, protection, and efficiency optimization.

Conclusion

In summary, the comprehensive understanding of induction motor parameters, proper experimental procedures, and theoretical foundations are crucial in evaluating motor performance. These insights not only assist in optimizing operation and efficiency but also provide a foundation for developing advanced starting techniques, control strategies, and applications in modern industry. The experimental analysis, supported by theoretical validation, demonstrates the importance of proper winding configurations, load management, and measurement techniques in achieving reliable and efficient motor operation.

References

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