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Unformatted text preview: Scott R. Smith ENEE473 Lab 8: Single-Phase Induction Motor April 6, 2007 Purpose: The single-phase induction machine runs more efficiently on one phase than the three- phase machine runs on one phase. The mechanical characteristics of the single-phase machine will be presented. 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. Multimeter The multimeter will mainly be used to check actual resistance values and measure voltages. Single-Phase Induction Machine The induction machine (IM) is very similar to a transformer with the secondary winding shorted. With only a single phase, the field does not naturally rotate. Therefore, the IM usually has an auxiliary winding that is used to start the IM. The auxiliary winding must be shifted by 90 degrees in space and time. By shifting the current phase, a torque is created between the stator and rotor fields. The torque is what starts motion in the IM. After the IM passes the speed that corresponds to maximum torque, the auxiliary winding is usually turned off by a centrifugal switch. Only one phase is needed to run the IM. The ratings of the machine are 1 HP , 750 W , 120 V , and 17 A . 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. 2. Set up the DCD to measure torque. Loosen the winged bolts on the back of the DCD to allow the outer chassis of the DCD to rotate. On the torque meter in front of the DCD, tighten down the eyelet to the correct height so that when the pin is inserted, it does not touch the inner edge of the eyelet. Insert the pin....
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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