When purchasing ABB motors, it is inevitable to be asked by the supplier to provide selection parameters. The uncertain answers may reveal our poor professionalism, at the meantime, cause unnecessary misunderstandings in the communication, which may lead to the unsatisfactory performance of the procured item. Actually the basic parameters we need to know for model selection only are rated power, rated voltage, rated speed and other conditions. Asynchronous motors have obvious advantages in the usage, thus winning the favors of the customers. It has a simple structure, which is approved by an experienced technicians in our workshop saying that the working hours for assembling one DC motor can afford to complete two synchronous motors or four asynchronous motors of almost the same power. Due to its reliable performance, only half cost of other brands, the simplest manufacturing process and convenient maintenance, the asynchronous motor has been most widely used in the industry. Asynchronous motors are further divided into squirrel-cage motors and wound-type motors with the different use of the rotor. The rotor of squirrel cage motor is made of metal strip, copper or aluminum. Aluminum is relatively cheap, and has rich reserve in China, so aluminum rotor is widely used in the conditions with no strict requirement. But copper has better performance in the mechanical properties and electrical conductivity than aluminum, therefore it is the most common used type as I have learned. Squirrel cage motor has superior reliability than wound-type motor because it has solved the problem of discontinuation in the process. However, it also has a disadvantage, that is the metal rotor obtains a small torque by cutting the magnetic induction line in the rotating stator magnetic field, as well as a large starting current, so it cannot bear the load with large starting torque demand. Next, I will give a detailed explanation of the ABB motor selection parameters separately, for reference only. 1. Rated Power When purchasing, it is often asked how big the motor is, that generally refers to the rated power in stead of the size of the ABB motor. This is the most important indicator to quantify motor’s ability, also the necessary parameter required for model selecting. (for rated power, for rated voltage, for rated current, cos θ for power factor, η for efficiency) The principle in correctly selecting the motor capacity is to choose the most economic power under the premise that the motor can satisfy the manufacture equipment load. Choosing too large power will increase the equipment cost and bring in unnecessary waste, furthermore, frequent underruns will result in low efficiency and AC motor power factor; conversely, if the power is selected too small, the motor will run overloaded and have premature damage, then it will bring about project delay and extra engineering cost, finally cause a decline in overall profit. 2. Rated voltage The rated voltage of ABB motors refers to the line voltage at rated operating mode. The choice of the rated voltage of the motor depends on the power supply voltage from power system and motor capacity. While the AC motor voltage grade selection is mainly based on the power supply voltage level in the use place. Generally, the low-voltage network is 380V, so the rated voltage is 380V (Y or ? connection method), 220/380V (?/Y connection method), and 380/660V (?/Y connection method). Even if the power of the low-voltage motor is increased to a certain degree (such as 300KW/380V), the current is difficult to be enlarged due to the limitation of the wire bearing capacity, also cause the cost too high. 3. Rated speed The rated speed of the ABB motor is the speed in the rated operating mode. Both the motor and the machine driven by it have their own rated speeds. The selected motor speed should meet the user’s need. The lower the motor speed is, the higher the number of stages and the larger the volume of the motor are, and the price will rise accordingly. In opposite, the improperly high speed will lead to more complicated transmission mechanism and the maintenance cost will increase exponentially. In addition, the motor torque is inversely proportional to the rotational speed under a certain power. Therefore, the user with loose requirements on start-up and braking can make a comprehensive comparison with several different rated speeds from the initial investment, floor space and maintenance cost of the equipment, and finally determine the most suitable rated speed; this will not only save the initial investment, but also reduce the occurrence of motor damage in operation; but for the operation requiring frequent start, brake and reversal, but the duration of the transition process has little effect on productivity, the ration and rated speed selection is mainly based on the least transition process loss as well as the initial investment. For example, the hoist motor needs frequent positive and negative reversal with very large torque, the rotation speed is very low, and the motor size is big, then it is relatively expensive. The first-level critical speed of ABB motors is generally above 1500 rpm, so the effect of critical speed could be neglected for conventional low-speed motors. However, the 2-level high-speed motor has a rated speed approaching 3000 rpm, it is suggested to consider the effect and avoid to use motor for a long time in the critical speed range. Generally, the motor can be roughly determined by providing the rated power, rated voltage, and rated speed of the motor. But if you want to optimally meet the load requirements, these basic parameters are far from enough. The other parameters need to be provided include: frequency, working system, overload requirement, insulation level, protection level, moment of inertia, load resistance torque curve, installation method, ambient temperature, altitude, outdoor requirements, etc., according to the specific situation. Hope this content could help you a little in the purchase of the motor, and welcome to forward this article and share it.
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