The Ultimate Buyer's Guide for Purchasing Rotor Motor

Induction motors are popular in the industry, since they are simple to build and economical. The following are some essential things you need to consider when buying an induction motor.

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What is an Induction Motor?

An induction motor or an asynchronous motor is an AC motor that works on the principle of electromagnetic induction. That is, the rotor obtains torque under the action of the rotating magnetic field generated by the stator, and then the rotor rotates. Since the rotor speed is not the same as the speed of the rotating magnetic field (synchronous speed), the induction motor is also known as asynchronous motor.

The rotor is a rotatable conductor, which is divided into squirrel-cage type and wound type according to the winding form. The stator is the stationary part of the motor which provides a rotating magnetic field. The rotating magnetic field is realized through the alternating current. When the current flows through the coil of the rotor, the properties of the magnetic poles are cyclically changed, which is equivalent to a rotating magnetic field. Depending on the the input supply, induction motors can be categorized into single-phase and three-phase induction motors.

Single-phase induction motors are squirrel-cage types, which are mainly used for small loads, such as fans, washing machines, refrigerators, air conditioners and other household appliances.

Three-phase induction motor rotors include squirrel-cage type and wound type. They are widely used as industrial drives due to its low price, sturdy structure, low maintenance cost, high efficiency, easy operation, reliability and durability.

Choosing an Induction Motor

When buying an induction motor, the primary concerns are speed, voltage, torque and power. Other things you've got to take into consideration are working system, overload requirements, insulation class, protection class, moment of inertia, load, installation method, maintenance, ambient temperature, altitude, enclosure rating, outdoor environments, energy efficiency, etc. Now, ATO provides you with its reliable and economical induction motors and helps you make best choices in your purchases.

1-Phase Induction Motors

An induction motor using a single-phase AC power supply is called a 1-phase induction motor. Because single-phase induction motors only need single-phase alternating current, they are easy to use and widely used, and have the advantages of simple structure, low cost, low noise, and little interference to radio systems, so they are often used in household appliances and small power machinery with low power. Among them, such as electric fans, washing machines, refrigerators, air conditioners, range hoods, electric drills and medical equipment.

3-Phase Induction Motors

Three-phase induction motor is a kind of induction motor, which is powered by three-phase AC current. Compared with single-phase induction motors, three-phase induction motors have better running performance and can save various materials. Three-phase induction motor are mainly used in excavation, fluid transportation and other fields that need to provide power, such as machine tools, small and medium-sized steel rolling equipment, fans, pumps, light industrial machinery, metallurgy and mining machinery, etc.

Explosion Proof Motor

Explosion-proof motor is a kind of motor that can be used in flammable and explosive places and does not produce electric sparks when running. Explosion-proof motors are mainly used in coal mines, oil and gas, petrochemical and chemical industries. In addition, in the textile, metallurgy, city gas, transportation, grain and oil processing, paper, medicine and other sectors are also widely used. As the main power equipment, explosion-proof motors are usually used to drive pumps, fans, compressors and other transmission machinery, etc.

Brake Motor

The brake motor is a fully enclosed self-fan-cooled squirrel cage type three-phase asynchronous motor with an additional disc type DC brake. It is composed of a DC disc electromagnetic brake motor attached between the rear end cover of the Y series motor and the fan. It is a derivative series of the Y series. It has the advantages of rapid braking, simple structure, high reliability and strong versatility. Brake motors are widely used in various mechanical equipment and transmission devices that require quick stop and accurate positioning.

Variable Speed Motor

A variable speed motor is a motor that changes the speed of the motor by changing the number of stages, voltage, current, frequency, etc. of the motor, so that the motor can achieve higher performance. Due to its excellent performance, variable speed motors have been widely used in steel, power stations, cables, chemicals, petroleum, cement, textiles, printing and dyeing, papermaking, machinery and other industrial sectors for stepless speed regulation of load machinery with constant torque or decreasing torque.

Stainless Steel Motor

The stainless steel motor is designed to avoid flats, cracks and crevices, preventing the accumulation of foreign objects and bacteria. Its housing and cables can withstand daily high pressure, high temperature and aggressive chemical washdowns. The robust design means the motor can be cleaned without the need for guards and covers to protect it. These features ensure faster cleaning, higher uptime, and higher overall line equipment efficiency.

Induction Motor Advantages and Disadvantages

Advantages:

• Various control methods: Since induction motor has no permanent magnet, it is easier to achieve different speeds and torques by weakening magnetic field or frequency conversion, etc. It can be used in industrial or domestic applications that do not require high torque density, and has the advantages of self-starting, economical, and reliable.
• Low cost: Induction motors are cheap compared to synchronous and DC motors. This is determined by the design of the induction motor. Therefore, induction motors are the first choice for fixed speed applications in industry, as well as for commercial and domestic applications where AC power can be easily connected.
• Low maintenance cost: The structure of the induction motor is simple, so the maintenance is also easy, which reduces the maintenance cost.
• Easy to operate: Induction motors are self-starting motors (runs on their own with alternating current). It operates easily since there is no electrical connector on the rotor.
• Speed variation: The speed variation of an induction motor is constant. Speeds vary by only a few percent from no load to rated load.
• High starting torque: Induction motors have a high starting torque, which allows a load to be applied before the motor starts. Three-phase induction motors have a different self-starting torque than synchronous motors. However, a single-phase induction motor has no self-starting torque and can only be rotated by using some auxiliary means.
• Durability: Another advantage of induction motors is durability, which allows the motor to operate for many years without any cost and maintenance.

Disadvantages:

Compared to permanent magnet motors, induction motors are less efficient because of the current heat loss caused by the induced current.

1. AC motors:

AC motors are the most popular in the industry as they have several advantages:

• They are simple to build
• They are more economical due to lower start-up consumption
• They are also sturdier and therefore generally have a longer lifespan
• They require little maintenance

Because of how they operate, which involves synchronization between the rotor rotation and current frequency, the speed of AC motors remains constant. They are particularly suited for applications requiring continuous movement and few gear changes. This type of motor is therefore perfectly adapted for use in pumps, conveyors and fans.

They can also be integrated into systems that do not require high accuracy if they are used with variable speed.

On the other hand, speed control functions make them more expensive than other motors.

There are two types of AC motors: single-phase and three-phase.

• Single-phase motors are characterized by:
  • The electrical power (in kW), which will determine the torque
  • The number of poles, which will give the rotational speed
  • The attachement method: flange (B14, B5) or brackets (B3)
  • Efficiency
  • Less industrial as they are less powerful
  • They can be used on the domestic electricity grid.
• Three-phase motors are characterized by:
  • An architecture that allows much greater electrical power to be transmitted than a single-phase voltage motor
  • Their use in industrial environments (about 80%)
  • Their use for infrastructure and equipment requiring high electrical power

2. DC motors:

DC motors are also very common in industrial environments because they have significant advantages depending on the format (see brushless motor question):

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• They are accurate and fast
• Their speed can be controlled by varying the supply voltage
• They are easy to install, even in mobile (battery-powered) systems
• The starting torque is high
• Starting, stopping, accelerating and reversing are done quickly

They are very well suited for dynamic applications requiring high accuracy particularly in terms of speed, as in the case of elevators, or in terms of position as in the case of robots or machine tools.

They can also be advantageous for applications requiring high power (10,000 kW for example).

However, they have certain disadvantages depending on their structure compared to AC motors:

• They are less common because they are less suitable for applications requiring high power
• They are made up of many parts that wear out and are expensive to replace

2. Brushless motors

Brushless motors make up for some of the weak points of brushed motors, such as the presence of brushes. But these motors also have other advantages:

• They can operate at higher speeds (up to 100,000 rpm compared to 20,000 rpm for brushed motors).
• They have a longer service life (over 10,000 hours of operation)
• They are more reliable and efficient.
• There are no wearing parts except for the bearings, which reduces maintenance operations.

The fact that these motors are able operate at very high speeds makes them particularly suitable for grinders, fans or saws.

Brushless motors are systematically equipped with an encoder, a sensor that allows for electronic switching and determination of the rotor position. These motors are therefore perfect for servomotor precision applications.

However, they have certain disadvantages:

• The initial cost is high because it is necessary to integrate a dedicated switching device (controller).
• They also generally require a gear reducer in drive applications.

Is this the end of brushed motors? Not according to the Opportunity rover

It might seem that in the match between brushed motors and brushless motors, the brushed ones would lose and have no choice but to go back to the closet. This is not the case, however, as brushed motors remain popular in industry and even in space. Maxon, a Swiss manufacturer of electric motors, is constantly developing new technologies for brushed motors and their brushed motors equipped Opportunity, NASA’s rover sent to Mars in .

Opportunity took 34 DC brushed motors onbord which have been able to operate successfully under extreme conditions with wide temperature variations. NASA’s choice was simple: to benefit from the simplicity of brushed motor control and therefore have the ability to control all 34 motors from a single controller. Brushless motors would have required one controller per motor with risks of costs and complications.

A stepper motor converts an electrical pulse into an angular motion. It is useful for applications requiring open loop position control.

There are three categories of stepper motors:

• The variable reluctance motor: With the same electrical characteristics, this type of motor is less powerful but faster than a permanent magnet motor.
• The permanent magnet motor: it is a low cost, low resolution motor
  average (up to 100 steps/revolution).
• The hybrid motor:  this type of motor combines the two previous types of technology but is more
  expensive. It has the advantage of better torque and higher speed. It has a resolution of 100 to 400 steps/revolution.

Permanent magnet and hybrid motors are the most commonly used motors because they have certain advantages:

• They are accurate
• They are inexpensive
• They are sturdy
• Simple construction
• The torque is high at start-up and at low speeds

However, they also have some disadvantages:

• The speed and torque are relatively low
• Torque decreases sharply as speed increases
• They generate vibrations that can create resonance problems
• There is a risk of overheating

When selecting a stepper motor, it is important to take into account:

• Torque and load
• The number of steps
• The dimensions of the motor (weight, mounting flanges, etc.).
• Cost

Manufacturers are increasingly contemplating the question of energy efficiency. A greener and more environmentally friendly economy is one of the objectives of the United Nations Climate Change Conference which many States committed to. But it is above all in order to limit consumption and for savings that industry has been acquiring more energy-efficient equipment in recent years. According to a study by the European Commission, motors account for 65% of industrial energy consumption in Europe. Taking action when it comes to motors is therefore an important step in order to reduce CO2 emissions. The Commission even predicts that it is possible to improve the energy efficiency of European-made motors by 20 to 30% by . The result would be 63 million tonnes less CO2 in the atmosphere and 135 billion kWh saved.

If you also want to integrate energy-efficient motors and get savings while contributing to the planet, you will first need to look at the energy efficiency standards for motors in your country or geographical area. But be careful, these standards do not apply to all motors, only to asynchronous AC electric motors.

International standards

• The International Electrotechnical Commission (IEC) has defined energy efficiency classes for electric motors placed on the market, known as the IE code, which are summarized in the international IEC standard
• The IEC has identified four levels of energy efficiency that define a motor’s energy performance:
  • IE1 refers to STANDARD efficiency
  • IE2 refers to HIGH efficiency
  • IE3 refers to PREMIUM efficiency
  • IE4, still under study, promises SUPER PREMIUM efficiency
• The IEC has also implemented the IEC -2-1: standard for testing electric motors. Many countries use national test standards, while also referring to the international IEC -2-1 standard.

In Europe

The EU has already adopted several directives aimed at reducing the energy consumption of motors, including the obligation for manufacturers to place energy-efficient motors on the market:

• Class IE2 has therefore been mandatory for all motors since
• Class IE3 has been mandatory since January for motors with a power of 7.5 to 375 kW (or IE2 if these motors have a frequency inverter)
• Class IE3 has been mandatory since January for motors with a power of 0.75 to 375 kW (or IE2 if these motors have a frequency inverter)

In the United States

In the United States, the standards defined by the American association NEMA (National Electrical Manufacturers Association) are in force. Since , the minimum level required has been set at IE2.
The same classification applies to Australia and New Zealand.

Asia

In China, the Korean MEPS (Minimum Energy Performance Standard) standards have been applied to small and medium-sized three-phase asynchronous motors since (GB ). In , MEPS standards were harmonized with IEC standards, moving from IE1 to IE2 and now to IE3.

Japan has harmonized its national regulations with IEC efficiency classes and included IE2 and IE3 electric motors in its Top Runner program in . Introduced in , the Top Runner program forces Japanese manufacturers to constantly offer new models on the market that are more energy efficient than previous generations, thus forcing emulation and energy innovation.

India has had a comparative efficiency label since and a national standard at an IE2 level since .

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