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Unformatted text preview: Scott R. Smith ENEE473 Lab 7: Single-Phase Induction Motor (Using the Three-Phase Induction Motor) March 30, 2007 Purpose: The three-phase induction machine runs most efficiently with a three-phase supply. The machine can be run on a single phase, but the efficiency should not be as great. In this experiment, I will show the efficiency of the three-phase induction motor being run on a single phase. Devices and Instrumentation: Resistor Banks Each bank of resistors is made up of ten individual resistors that can be connected together using single pole double throw switches. By systematically setting the switches it is possible to create many resistance values by combining series and parallel branches in one bank. Each resistor has a power dissipation rating of 100 W and a resistance value of 250 . The power dissipation capacity can be increased by using parallel branches of resistors to achieve the same value as a series connection would. Wattmeter The wattmeter is a three-terminal device where two terminals are connected in-line with the circuit to measure current and the third terminal measures voltage of the in-line voltage relative to the connected node. There are two wattmeters at the lab station. Using both of them, three-phase power can be measured. Three-Phase Induction Machine The induction machine (IM) is very similar to a transformer with the secondary winding shorted. I am assuming that the induction machine is viewed as a balanced Y load. The stator has three-phase windings distributed in space and time by 120 degrees. When the three-phase windings are excited from a three-phase source a rotating magnetic field is created. The rotating field interacts with the rotor by inducing a voltage across the bars in the rotor. The induced voltage creates current in the rotor which lags the voltage applied to the stator. The rotor current produces a rotor reaction magnetic field which interacts with the stator magnetic field. The rotor field continuously tries to align with the stator field. Torque is produced because the rotor reaction field always lags the stator field. The ratings of the machine are 1 kW , 208 V , 6.2 A , and 1770 RPM . DC Dynamometer The DC dynamometer (DCD) is a direct current machine. It can be mechanically coupled to the IM using plastic pins and collars. The DCD can be used to measure torque, lock the rotor, be a prime mover, and act as a mechanical load. The rating of the DCD is 1 kW . Experimental Procedure: I. Clockwise Rotation of the IM 1. Mechanically couple the IM and the DCD. Insert the plastic pins and tighten the collar between the IM and DCD. Make sure the synchronous machine is decoupled from the DCD....
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This note was uploaded on 05/04/2008 for the course ENEE 473 taught by Professor Mayergoyz during the Spring '07 term at Maryland.
- Spring '07