2013 Induction Motor Thermal Model Pdf Converter
How does an Induction Motor Work ? They are cheaper, more rugged and easier to maintain compared to other alternatives. In this video we will learn the working of a 3 phase squirrel- cage induction motor. The following article gives a detailed description of the video lecture. Parts of an Induction Motor. An induction motor has 2 main parts; the Stator and Rotor. The Stator is the stationary part and the rotor is the rotating part. The Rotor sits inside the Stator. There will be a small gap between rotor and stator, known as air- gap. The value of the radial air- gap may vary from 0. The way the steel laminations are arranged inside the frame is shown in the following figure. Here only few of the steel laminations are shown. Winding passes through slots of the stator. It produces a rotating magnetic field (RMF). As shown in the figure below a magnetic field is produced which is rotating in nature. RMF is an important concept in electrical machines. We will see how this is produced in the next section. A wire carrying current produces a magnetic field around it. Now for this special arrangement, the magnetic field produced by 3 phase A. C current will be as shown at a particular instant. Two more instances are shown in the following figure, where due to the variation in the A. C current, the magnetic field also varies. It is clear that the magnetic field just takes a different orientation, but its magnitude remains the same. From these 3 positions it’s clear that it is like a magnetic field of uniform strength rotating. Revised 26 January 2013. The thermal model of the induction motor presented here also has the. Simulation and validation of the thermal model. Semiconductor Components Industries, LLC, 2013. 3-phase Brushless Motor Driver. Thermal shutdown operating. The speed of rotation of the magnetic field is known as synchronous speed. The E. M. F will produce a current through the loop. So the situation has become as if a current carrying loop is situated in a magnetic field. This will produce a magnetic force in the loop according to Lorentz law, So the loop will start to rotate. Here instead of a simple loop, something very similar to a squirrel cage is used. A squirrel cage has got bars which are shorted by end rings. So as in the previous case, current will be induced in the bars of the squirrel cage and it will start to rotate. You can note variation of the induced current in squirrel cage bars. This is due to the rate of change of magnetic flux in one squirrel bar pair which is different from another, due to its different orientation. This variation of current in the bar will change over time. You can note one big advantage of 3 phase induction motors, as it is inherently self starting. You can also note that the bars of a squirrel cage are inclined to the axis of rotation, or it has got a skew. This is to prevent torque fluctuation. If the bars were straight there would have been a small time gap for the torque in the rotor bar pair to get transferred to the next pair. This will cause torque fluctuation and vibration in the rotor. By providing a skew in the rotor bars, before the torque in one bar pair dies out, the next pair comes into action. Thus it avoids torque fluctuation. The Speed of Rotation of a Rotor & the Concept of Slip. You can notice here that the both the magnetic field and rotor are rotating. But at what speed will the rotor rotate? To obtain an answer for this let's consider different cases. Consider a case where the rotor speed is same as the magnetic field speed. The rotor experiences a magnetic field in a relative reference frame. Since both the magnetic field and the rotor are rotating at same speed, relative to the rotor, the magnetic field is stationary. This means zero force on the rotor bars, so the rotor will gradually slow down. But as it slows down, the rotor loops will experience a varying magnetic field, so induced current and force will rise again and the rotor will speed up. In short, the rotor will never be able to catch up with the speed of the magnetic field. It rotates at a specific speed which is slightly less than synchronous speed. The difference in synchronous and rotor speed is known as slip. Energy Transfer in the Motor. The rotational mechanical power obtained from the rotor is transferred through a power shaft. Various components of these losses are friction loss, copper loss, eddy current and hysteresis loss. Such energy loss during the motor operation is dissipated as heat, so a fan at the other end helps in cooling down the motor.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
November 2016
Categories |