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Induction motor – The Ultimate Guide 2019

If you’re in the compressor, pumps, fans, conveyors, material handling, machine tool applications, then most definitely, you need an induction motor. It provides an effective way of power to drive this equipment.

More importantly, going for a continuous duty working will increase productivity, efficiency, and accuracy. But, how can you choose the most reliable, and the high-quality induction motor that meets all safety standards? Well, let’s find out.

What is an induction motor?

Induction motor an AC electric motor, It is a device that places a rotor in a rotating magnetic field and obtains a rotational moment under the action of a rotating magnetic field, thereby rotating the rotor.

An induction motor can, therefore, be made without electrical connections to the rotor.

The rotor is like a squirrel cage, also called a squirrel cage motor. The induction motor invented in 1887 by electrical engineer Nikola Tesla.

Hordu three induction motors

How does the induction motor work?

In short, electromagnetic induction produces a rotating magnetic field that drives the rotor of the induction motor to rotate.

The induction motor rotates to drive the pulverize, centrifugal pump, reducer, mixer, air compressor, and other equipment.

Thereby achieving energy conversion. It’s really simple and easy to understand, the question then comes up: How do you find and learn more about the working principle of an induction motor?

Can induction motor run at synchronous speed?

The induction motor always runs at a speed lower or higher than synchronous speed.

In other words, the induction motor can not run at synchronous speed, that’s why we also called it Asynchronous Motors.

Synchronous speed means the speed of the rotating magnetic field in the stator.

Induction motor working principle diagram

What are the types of an induction motor?

Depending on the type of input voltage, there are typically two types of induction motors –

1. Single phase induction motors
2. Three phase Electric motors

single phase induction motor

Hordu Three phase induction motor

We can also divide according to the rotor type –

1. squirrel cage induction motor
2. slip ring induction motor or a wound-rotor induction motor

What are the parts of an induction motor?

The induction motor has three main parts, the rotor, the stator, and the outer casing.

The stator and rotor complete the work and the outer casing protect the rotor and stator.

Induction Motor Stator:

1. The stator is the stationary part of the induction motor or generator. It consists of three parts: the stator core, the stator winding, and the base.

1.1 Stator core: It is the magnetic circuit part of the motor and is fixed inside the base. The stator core is laminated with a 0.35-0.5 mm silicon steel sheet, and the silicon steel sheet is coated with an insulating varnish. It can effectively reduce eddy current loss and hysteresis loss.

2. Stator winding: It is the circuit part of the motor, and the coil of the insulated wire is inserted into the slot of the stator core. The stator windings are directly connected to the power source, and each set of coils becomes an electromagnet with the surrounding steel core, generating a rotating magnetic field. Electromagnetic induction is the basic principle of induction motor operation.

Depending on the shape of the coil winding and the way in which the coil is wound, the stator windings of an induction motor are usually of two types:

1. Centralized winding, simple to produce, but low efficiency and poor running performance.
2. Distributed winding, the stator of the distributed winding has no convex poles, each pole is regularly embedded and wired by one or several coils, and the magnetic poles of different polarities are generated after being energized, so it is also called hidden pole winding.

AC motors usually use distributed windings.

Finished spare induction motor stator workshop

100% copper winding induction motor stator

Induction Motor Frame

there are 2 types of induction motor apart with frame material, cast iron induction motors and aluminum electric ac motors.

The outer casing consists of a frame and front and rear end caps.

The stator is mounted within the frame and the rotor is mounted inside the stator with a slight air gap separating it from the stator.

There is no physical connection between the rotor and the stator.

The housing protects the internal parts of the induction motor from water, dust and other environmental factors.

The degree of protection depends on the type of enclosure.

Generally, the protection level of three-phase induction motor and single-phase induction motor is IP54, IP44, and the protection grade of explosion-proof induction motor is IP65.

The outer casing is usually cast iron, the large asynchronous motor casing is welded with steel plates, and the micromotors are also cast aluminum casings.

The housing of the enclosed motor has a heat dissipation rib to increase the heat dissipation area.

The end cover of the protective motor has a venting hole for convection of the air and good heat dissipation performance.

Large electric motor housing warehouse

Induction Motor Rotor

The rotor is a rotatable conductor comprising a rotor core, a rotor winding and a rotating shaft.

1. The rotor core is also a part of the magnetic circuit of the motor, which is made up of silicon steel sheets with a thickness of 0.5 mm, and the iron core is fixed on the rotating shaft or the rotor bracket.
2. The rotor winding is a coil group that is wound in a regular manner in the motor and is fixed inside the stator.

There are generally two types of rotor windings for AC asynchronous motors, cage rotors and wound rotors. The rotor is a rotatable conductor comprising a rotor core, a rotor winding, and a rotating shaft.

1. The rotor core is also a part of the magnetic circuit of the motor, which is made up of silicon steel sheets with a thickness of 0.5 mm, and the iron core is fixed on the rotating shaft or the rotor bracket.
2. The rotor winding is a coil group that is wound in a regular manner in the motor and is fixed inside the stator.

There are two types of rotor windings for AC asynchronous motors, squirrel cage rotors and wound rotors.

Types of induction motor rotors

squirrel-cage rotor

The squirrel-cage rotor structure is relatively simple.

Generally, a rotor coil made of copper or aluminum is cast in a cage-shaped groove on the rotor core.

It is a closed loop and does not physically connect with other parts.

The main function is to suppress the stator, Current. Small and medium-sized rotors are generally cast aluminum.

The induction motor of 100KW or more is welded by copper strips and copper end rings.

In order to improve the starting performance, the squirrel cage type can also be made into a deep groove rotor and a double squirrel-cage rotor to meet special needs.

There is no winding on the squirrel cage rotor, the maintenance cost is low, the manufacturer is convenient, and the service life is long.

It has a wide range of applications in many fields. wound rotor The wound rotor has a complicated structure and high price, and the control motor operation is relatively complicated.

However, the winding motor has a large running torque because of its starting and is generally used in small starting current, large starting torque, or smooth speed regulation and heavy load.

Squirrel-cage rotor VS Wound Rotor

Applications of induction motor

Induction motors are widely used in industrial and household appliances because they are self-starting, reliable and economical, More importantly, they have almost no maintenance costs.

So if you are looking for a reliable and professional electric motor manufacturer and supplier  – think of Hordu.

• Pumps
• Compressors
• Mixers
• Lifts& Hoists
• Cranes
• Large capacity exhaust fans
• Driving lathe machines
• Crushers
• Oil extracting mills
• Textile and etc.

Induction motor for industrial

Although traditionally used in fixed-speed service, induction motors are increasingly being used with variable-frequency drives (VFDs) in variable-speed service.

VFDs offer especially important energy savings opportunities for existing and prospective induction motors in variable-torque centrifugal fan, pump, and compressor load applications.

Squirrel cage induction motors are very widely used in both fixed-speed and variable-frequency drive (VFD) applications.

VFD Induction Motor Assembly for Pumps

Starting methods of induction motor

There are three main ways to start the induction motor:

1. direct start,
2. buck start,
3. soft start
4. .variable frequency start.

Direct On Line Starter:

It is a common way of low-power induction motor below 18.5KW, and it is directly self-starting at rated voltage.

The starting current of Induction motors is six to seven times the full load current.

According to the specified starting power of a single motor, it should not exceed 30% of the capacity of the distribution transformer.

Direct start-up features: low investment, simple equipment, simple design, although the start is fast, the starting torque is small, the current is large.

Direct On Line Starter wiring

Buck Start: 1.Star-Delta Starter

Star-Delta Starter is preferred as a method of starting in Low starting Torque Applications.

Star-Delta Starter can reduce the starting current. IST(Y)/IST(△)=1/3, and the starting torque is also reduced to 1/3;  

Star-Delta Starter wiring

2. Autotransformer step-down start

The autotransformer step-down is to connect the high voltage side of the autotransformer to the grid and the low voltage side to the motor.

The voltage at the motor end can be adjusted freely.

After the speed rises to the rated speed, the motor is connected to the power supply and operates normally at the rated voltage.

Assuming that the voltage is 1/k of the rated voltage, the starting current is 1/k2 of the original, and the starting torque is also reduced to 1/k2.

The starting torque is larger than the star-delta step-down start, but it is not allowed to start frequently.

It is generally used for ultra-large capacity induction motors.  

Autotransformer step-down start wiring

  3. Extended Delta starts Extended Delta start:

When the stator winding starts, it is connected to a Yanbian triangle to reduce the starting current.

After the motor is started, it is replaced by a triangle to make the motor run at full pressure.

Induction Motor HS Code

The Harmonized System is an international nomenclature for the classification of products.

It allows participating countries to classify traded goods on a common basis for customs purposes.

Induction motor insulation class

Induction motor nameplate usually marked with insulation class B or F.

So what is the insulation class of the induction motor?

What is Class B insulation, Class F insulation?

Let Taizhou Hordu share with you.

The insulation grade refers to the heat resistance grade of the insulation material used inside the induction motor and is classified into Class A, Class E, Class B, Class F, and Class H.

The most common insulation class is Class B and Class F.

Mica, asbestos, glass filaments glued or impregnated are common Class B insulation materials.

According to experience, Class A materials have a life expectancy of 10 years at 105 ° C and Class B materials at 130 ° C.

However, under actual conditions, the ambient temperature and temperature rise will not reach the design value for a long time, so the general life span is 15 to 20 years.

If the operating temperature exceeds the ultimate operating temperature of the material for a long period of time, the aging of the insulation is intensified and the life is severely shortened.

Therefore, when the motor is running, the temperature is one of the main factors of life.

The specific allowable temperature rise of the motor Class B insulation, Class F insulation, etc. is as follows:

Induction Motor insulation temperature class chart

Temperature rise is the temperature difference between the motor and the environment and is caused by the heat generated by the motor.

Note: In practice, after the temperature is determined, we will use a higher level of insulation to improve the life of the motor.

For example, the commonly used insulation grade is Class B motor, and the insulation material used is often Class F to ensure the stability of temperature rise.

Hordu Induction Motor for Pipeline centrifugal pump

Duty Types (Load Cycle) Of Induction Motors

Duty Types (Load Cycle) Of Induction Motors chart

Induction motor maintenance

In order to ensure the normal operation of the motor and extend the service life of the motor, the motor must be regularly maintained.

But how do you regularly maintain the motor?

What is the significance of regular maintenance of the motor?

Next, we will briefly introduce the maintenance of the motor.

How to carry out regular maintenance of the motor: Very simple, just like caring for your car, In general, small maintenance is carried out in 2-3 months, and comprehensive maintenance is carried out once a year.

1. Motor maintenance items are:
2. Remove dust and attached dirt from the motor surface;
3. Clean the mesh of the motor hood to keep the air inlet and outlet open unobstructed;
4. Measure the insulation resistance of the motor.
5. The comprehensive maintenance project of the motor has:
6. All items of small motor maintenance;
7. Replace the damaged bearing; if necessary, clean the open bearing and replace the grease;
8. Clean the internal motor to make the stator winding of the motor clean, free of oil and copper;
9. Cleaning or replacement of other parts of the motor.

The meaning of regular maintenance of the motor:

1. The motor runs efficiently
2. The service life of the motor is extended
3. The workers around the motor have better safety protection

Hordu Y2-112M-4 induction motor

Conclusion

As you can see, Hordu induction motor is important equipment in the Aggregate & Cement, food processing, Pharmaceutical, Oil, Gas and chemical industries.

However, to choose a high quality and reliable induction motor, you need to understand every aspect mentioned in this guide.

That way, you will get the best induction motor for your specific needs.

So I believe that having gone through this whole guide, you can get the three phase induction motor and single phase induction motor.

For free consultations on induction motor, contact us or send mail to sales@hordu.com directly today.