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Experimental investigation into the operating characteristics of three phase induction motors

Foote, Charlie (2014) Experimental investigation into the operating characteristics of three phase induction motors. Other thesis, Murdoch University.

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Induction motors are used in a significant portion of industrial electric drive applications due to their reliability, relatively low cost and low maintenance required. The Squirrel Cage and Wound Rotor type machines are common examples of an induction machine.

One of the important features of an induction motor is its torque speed characteristic. The correct application, motor protection, speed control and efficiency of a machine can depend on correctly identifying this characteristic.

The project objective involved the design of experiments to obtain the torque speed characteristics for both the squirrel cage and wound rotor type induction motors available in the engineering laboratory. A further aim of the project involved the design and execution of suitable experiments with the Lab-Volt equipment to experimentally determine the electrical parameters of the machines. Determining the electrical parameters involves conducting standard tests such as the DC, No-Load and Locked Rotor test.

Once these parameters are known the characteristic curve can be modeled by simulation software and a comparison can be made with the experimental curves. Further work included using 3 measured points within the stable operating region to extrapolate the maximum torque and speed for each machine. An investigation into the effect of increasing the rotor resistance in the wound rotor induction motor (WRIM) was also carried out.

Determining the torque speed characteristic experimentally was achieved relatively easily in the stable operating region with the use of an electrodynamometer as a loading device. Torque measurements are read directly from the scale on the faceplate of the electrodynamometer whilst simultaneously measuring the rotational speed with an optical tachometer.

Determining the T-S characteristics in the unstable region of operation included coupling the machine being tested to a DC generator. The torque speed characteristic of a DC machine is linear up until the armature windings are saturated. Measurements of the power output (P=V*I) of the armature windings and the rotational speed are taken and the induced torque can then be calculated.

Matlab was used in the implementation of this project as a simulation tool. Three simulations programs were written including: a program to plot the torque speed curve derived from the equivalent circuit, a program to conduct a sensitivity analysis of the measured parameters and thirdly, a program to determine the electrical parameters and max torque and speed using just three measured points on the curve.

Publication Type: Thesis (Other)
Murdoch Affiliation: School of Engineering and Information Technology
Supervisor: Hettiwatte, Sujeewa
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