How does a 3 Phase Induction Motor work? - Technical animation

Three-phase induction motors are the most commonly used AC motors. With its ability to produce high torque with simple construction, relatively low cost and robustness, this motor gets high popularity. The basis for this induction motor is the RMF which is built in the stator. How RMF is built was explained in another video. Please check out our playlist. The rotor the moving part of the machine exists of conducting bars with endcaps on each side. That's why he has the appearance of a squirrel cage. Therefore these motors are also named as squirrel cage motor. As the stator magnetic field rotates Voltage is induced within the bars of the rotor. As the rotor bars are shortened at both ends, there is a closed path for the flow of current. This in turn produces its own magnetic field in the rotor bars, which opposes the magnetic field of the stator. The direction of the force as a result of the interaction between stator and rotor field can also be determined by the Lorentz law. Torque can only be created when rotor voltage is induced. To say it in another word: The rotor always has a rotating speed minor to the RMF. This difference is called slip. To enhance the magnetic field of the rotor and therefore the torque, the rotor bars are mounted within a pack of steel laminations. Let us first consider the current characteristic. What you can see is the high starting current, which is about seven to ten times the rated current. Electrically three-phase asynchronous motors can be compared with a transformer. The stator forms the primary winding and the rotor a short-circuited secondary winding. For this reason three phase a synchronous motors often require startup aid. Star Delta and frequency converters are to be mentioned in the first place. As the rotational speed increases, the RMF cuts the rotor at a lower frequency and the motor current decreases inevitably. Several effects determine the course of this character is to curve. Once the three-phase asynchronous motor has reached its nominal speed, it can safely maintain its nominal speed even with increasing load. How so? Because the torque curve is steep in the nominal point. The synchronous speeds depends on the number of magnetic poles. High torque induction motors with high number of poles have lower sync speed. But as the number of poles increases the cost of manufacturing also increases. So you would perhaps use a motor with 2 or 4 poles, but bigger size to get the desired torque. The next section we discussed the basic information given by the nameplate. The International Electrotechnical Commission established standards for the information provided on the nameplate. The motors rated mechanical output power is given in kilowatts. Motor rated speed or full load rpm is the approximate rpm at which the rotor is rotating when the motor is operating under full load. With the information of the mechanical power and the rated speed you can calculate the rated torque by this equation. The motor rated current is the amount of amperage in the powerlines the motor needs, when it is operated at full load torque and mechanical output power. The motor operates with best efficiency when he driven by this rated frequency at which is designed to. Europe and India have 50 Hertz, America and Asia usually have 60 Hertz. To decide if this motor can be connected in Delta. Or should be connected in star you need the information about the rated motor voltage. In this case the motor can be connected in Delta within a 400 volt 3-phase power supply. Because the motor coils are connected to AC, you need the information for the effective power factor. The rated input power or electrical power can now be determined by a simple equation. The insulation class describes the thermal tolerance of the motor windings. The letter indicates the motor windings ability to withstand an operating temperatures for a specific length of time. Motors controlled by a variable frequency drive usually must have a higher insulation class. IP Ingress protection codes define how well an enclosure protects against the external environment. As the number gets higher the protection gets better. The first digit defines the protection level against solids, the second against liquids. You must use both digits to define an enclosure. Further information about your motor you get from the datasheet.

Channel: learnchannel

Views: 111,663

Keywords: induction motor, RMF, 3 phase induction motor, 3 phase motor, how an induction motor works, motor plate, motor characteristic curve, learnchannel

Id: b5tc0FrYk60

Length: 5min 19sec (319 seconds)

Published: Wed Mar 07 2018