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    Load Test on a 3 Phase Induction Motor

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    To obtain and analyse the performance characteristics of a 3 phase induction motor by load test.

    A 3 phase Induction motor supplied with the rated voltage (110v) plus two more values 90v and 115v. (4 poles) (results attached)

    Please see other attachment for calculations questions.
    Please expand on the discussion of results as much as possible.

    Supply the three-phase induction motor with the rated voltage via the transforme and record.

    Repeat the test for two more values of the input voltage.

    Calculate the output power at each load level.

    Calculate the total input power at each load level.

    Calculate the efficiency of the motor at each load level.

    Calculate the slip s at each load level.

    Construct following plots and discuss the results.

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    Solution Preview

    I don't quite know how you have derived or measured the input power as this would be related for a 3 phase motor by

    where is the power factor, unless of course power factor changes but this would only change with change in frequency. Anyhow based on what you have given me here is the best I can interpret these set of results for the induction motor in question

    Results are tabulated below where I have added additional rows to reflect the Torque developed by the motor based on a radial distance of from the axis of rotation and where torque is given as the product of measured force and the perpendicular radial distance of the motor armature

    I have also converted the measured angular speed of the motor in to using
    An additional row to each table of results is included showing the calculated output power developed by the motor using the equation for output power (in ) as the product of the developed torque and angular speed in ie using

    An additional row is included in each table of results to indicate the % motor efficiency given by the equation
    Finally one extra row is added to each table to indicate the calculated % motor slip at each measurement point using the equation

    where is the synchronous motor speed (angular speed under zero load conditions). It would appear that the synchronous speed in our case is and this is the value I have used in the calculations

    Rated Voltage (110v)
    Load 0 10 20 30 40 50
    Force (N) 0 0.6 1.9 3.4 4.8 6.2
    Torque (Nm) 0 0.15 0.475 0.85 1.2 1.55
    Va ...

    Solution Summary

    The expert examines the load test on a three phase induction motor.