![]() ![]() Use of this Concept Builder with our Task Tracker system allows teachers to track student progress. Each situation involves the same question: which direction will the meter stick rotate - clockwise, counter-clockwise, or not at all? Question-specific help is provided for each of the nine situations. The nine situations are organized into three different ability levels. There are nine different situations, each involving three torques, which learners must analyze. The Torque-ing About Rotation Concept Builder is a tool that challenges the learner to use information regarding force and lever arm for opposing torques in order to determine the direction that a beam would rotate. Hence, it is contained to disconnect the supply from the stator before entering the braking mode.Concept Builders » Rotation and Balance » Torque and Rotation And also, if the stator is connected with the supply, it is also generated as heat. Therefore, during the breaking, a very high amount of heat is generated. But the kinetic energy stored in the load is dissipated as heat. During braking mode, the slip is greater than one.īy this method, the motor stops within a short time. This method of electrical braking is known as plugging. Hence, the motor rotates in a reverse direction. In the braking region, the polarity of supply voltage is changed. During the generating region, the motor requires to supply reactive electric power. Hence, the machines receive mechanical energy and deliver electrical energy. The speed of a motor increases above synchronous speed with the help of external devices like a prime mover.ĭuring generating region, the slip and torque both are negative. In generating mode of operation, the induction motor runs above the synchronous speed and it behaves as an induction generator. The slip is zero at synchronous speed and the slip is one at standstill condition. Generally, the induction motor operates in this region. ![]() And the torque of a motor varies from zero to full-load torque as slip varies from zero to one.ĭuring this condition, the torque is directly proportional to the slip. When the stator is supplied by electric power, the rotor rotates below synchronous speed. In this mode of operation, the slip of an induction motor is between zero to one. Similar to the above description, this curve is also divided into three parts The torque-slip curve of the induction motor for constant rotor resistance is shown in the figure below. Therefore, the motor can handle overload for short period without stalling. The pull-out torque for an induction motor is 2 to 3 times of rated full-load torque for typical operation. The slip S M is a slip at the maximum torque point. Generally, the induction motor operates for the value of slip between zero to S M. This region in a torque-slip curve is decreasing region after the maximum torque point. If the motor continuously runs in this region, the motor will damage due to overheating. During this condition, the motor speed decreases, and the overload protection must be activated to disconnect a motor from the supply. This condition is when the load increases. ![]() If we increase the torque beyond the maximum torque point, the torque starts decreasing. This torque is known as pull-out torque or breakdown torque. The maximum torque is achieved when R 2 = sX 20. During this region, the curve shapes a rectangular hyperbola and passes through the point of maximum torque. So, the torque is inversely proportional to the slip. And in this condition, we can neglect the rotor resistance R 2. As the slip increases, the term (sX 20) 2 becomes high compared to Rotor resistance R 2. If the load increases, the speed of an induction motor decreases, and slip increases. In the low-slip region, the torque-slip curve is a straight line. This is the normal operating region for an induction motor. Hence, at low slip conditions, the torque is directly proportional to the slip. If we consider rotor resistance R 2 as constant ![]() When the slip is very low, (sX 20) 2 is negligible compared to the R 2. Therefore, an induction motor always runs slightly less than the synchronous speed. Hence, the torque developed in the rotor is zero. At synchronous speed, the slip of an induction motor is zero. ![]()
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