10 Things to Consider When Buying Asynchronous Motor Suppliers

AC induction motors are not often given the design consideration a machine deserves. The thought is "one size fits all" and the selection of a motor only depends on its voltage, power, and base speed. However, there are many other aspects to consider such as supply voltage, horsepower rating, and the application itself. What is the motor&#;s purpose and how is it going to make everything faster and more efficient?

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Induction motor fundamentals

The starting point for specifying a motor is the supply voltage, the horsepower rating, and the base speed for the particular application. Another important consideration is the enclosure. Will the motor have mounting feet, a flange on the drive end, or can it have both? What are the environment&#;s characteristics? Is rain or falling water a possibility? Is dirt or dust exposure a potential issue? In these instances, total enclosed fan cooled (TEFC) or total enclosed non-vented (TENV) motors are a good option. If the environment is clean and dry, an open drip proof (ODP) motor may be sufficient. 

Inverter duty considerations

Due to incentives from local power companies combined with the advantages and benefits of changing the operating speed of motors, variable frequency drives (VFDs) are becoming more common methods of controlling motors. In these cases, special consideration needs to be given to the "noisy" signal these devices produce. There are several features a motor suited for use with a VFD should have; however, two stand out at the top.

The first consideration is the voltage rating of the magnetic wire used in the motor windings. This rating can range from to V, with a common value of V. The greater the distance between the drive and the motor the greater the magnitude of the voltage spikes reaching the motor. A motor that has a V magnetic wire may have a reference to NEMA MG-1 , Part 31, Section 4, which states that a motor shall resist corona inception voltage (CIV) damage at voltages up to 1,600 V.

The second consideration may be the constant torque (CT) turn-down ratio of the motor, often listed a "xx:1 CT". This expresses how slow the motor can run and still deliver the same torque as it would at rated speed. Below this value the torque production capabilities of the motor decrease. For example, consider a 10 HP motor with a base speed of 1,800 RPM. It can produce 29 lb-ft of torque at rated speed (approximately RPM). If it has a 10:1 CT rating, it can produce that same torque down to 180 RPM. If it is a :1 CT, then it could produce 29 lb-ft of torque as low as 1.8 RPM.

Also ask how the motor stays cool if it has the typical shaft mount fan and the motor is running at a fraction of the rated speed. The fan doesn&#;t move much air at low speeds. Therefore, if the motor is running at low speed and producing high torque for an extended time, the motor will produce much heat and a different cooling method should be chosen-a blower-cooled motor. The blower has its own motor, separately controlled-not by the attached VFD. The airflow across the motor is constant and sufficient to keep the motor cool-even at low speed or zero speed. 

Choosing between horsepower and torque

The base speed of the motor is another important aspect when choosing an ac induction motor. It is common to see 2-pole ( RPM) and 4-pole ( RPM motors). However, 6-, 8-, and 12-pole (, 900, and 600 RPM) motors can be found as well. The base speed of a motor is related to the number of poles the motor contains by this equation: [RPM = (120 x design frequency) / # poles]. As a side note; although related, typically as the number of poles increase so does the size as well as overall costs.

Users might also want to swap speed for torque, depending on the application. In general, as the speed of the motor increases, the torque decreases, which is also true of gearboxes and belt and chain drives. This relationship is explained by this equation: [HP = (torque x base speed) / )].

The horsepower and base speed of the motor, along with any associated gearing, can be selected to meet the original goal, which is reducing the cost of equipment, size, and lead time for replacement components.

Charlie Medinger, power technical consultant, Consolidated Electrical Distributors. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, .

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Aspects such as supply voltage, horsepower rating, and the application itself should be considered when choosing an ac induction motor.

Harsh or wet conditions may require a special kind of ac induction motor for the particular application.

Base speed and torque also should be considered by the user, depending on the application.

Consider this

What other factors should be considered when choosing an ac induction motor for an application?

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-10-05    

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1. The choice of the principle of AC electric motor

In order to accommodate a variety of uses, electric motor manufacturers can produce different types, structure type and 

capacity of three phase asynchronous motor and synchronous motor. In the selection of AC electric motors, to fully consider their characteristics, carefully studied the characteristics of the driven machinery and equipment, select the load characteristics of the motor.

The principle of selecting the ac electric motor is:
1) According to the starting characteristics of the load and operating characteristics, select the most suitable for these characteristics of the motor to meet the production machinery in the process of the various requirements. 2) A motor having a protection class and a cooling method suitable for use in an environment of a place of use should be adapted to the environmental conditions in which the motor is located.
3) Calculate and determine the appropriate motor capacity. Usually designed and manufactured motor, the 75% -100% rated load, the highest efficiency. Therefore, the capacity of the equipment should be the smallest and the difference in the capacity of the selected motor, so that the power of the motor can be fully utilized.
4) select the high reliability, easy to maintain the motor.
5) taking into account the interchangeability, try to choose the standard motor.
6) In order to make the whole system run efficiently, consider the number of poles and the voltage level of the motor.

2. The general steps to buy an AC electric motor can be considered as follows:
1) According to the requirements of the production of mechanical, select the motor type. Such as asynchronous motor include squirrel cage induction motor, slip ring induction motor, variable frequency motor, brake motor.
2) Depending on the power supply, select the motor rated voltage.
3) According to the number of revolutions required by the production machinery and the transmission equipment, select the number of revolutions of the motor.
4) According to the motor and production machinery installation location and place environment, select the motor structure and protection form.
5) According to the load required by the power capacity and the motor running mode, select the rated power of the motor.

In the selection of ac electric motor, to take into account the above factors, and communicate with the electric motor manufacturer to select the most suitable motor.

The principle of selecting the ac electric motor is:1) According to the starting characteristics of the load and operating characteristics, select the most suitable for these characteristics of the motor to meet the production machinery in the process of the various requirements. 2) A motor having a protection class and a cooling method suitable for use in an environment of a place of use should be adapted to the environmental conditions in which the motor is located.3) Calculate and determine the appropriate motor capacity. Usually designed and manufactured motor, the 75% -100% rated load, the highest efficiency. Therefore, the capacity of the equipment should be the smallest and the difference in the capacity of the selected motor, so that the power of the motor can be fully utilized.4) select the high reliability, easy to maintain the motor.5) taking into account the interchangeability, try to choose the standard motor.6) In order to make the whole system run efficiently, consider the number of poles and the voltage level of the motor.2. The general steps to buy an AC electric motor can be considered as follows:1) According to the requirements of the production of mechanical, select the motor type. Such as asynchronous motor include squirrel cage induction motor, slip ring induction motor, variable frequency motor, brake motor.2) Depending on the power supply, select the motor rated voltage.3) According to the number of revolutions required by the production machinery and the transmission equipment, select the number of revolutions of the motor.4) According to the motor and production machinery installation location and place environment, select the motor structure and protection form.5) According to the load required by the power capacity and the motor running mode, select the rated power of the motor.In the selection of ac electric motor, to take into account the above factors, and communicate with the electric motor manufacturer to select the most suitable motor.

Contact us to discuss your requirements of Synchronous Generators Manufacturer. Our experienced sales team can help you identify the options that best suit your needs.