Pages

Tuesday, June 21, 2016

Introduction to THREE PHASE AND SINGLE PHASE Induction Motors

Learning Outcomes

          Understand the principles of induction motor operation
          Analyse composition and function of induction motors
          Perform different connection of single phase and three phase motor
          Troubleshoot induction type motors

Contents

        Three-Phase and Single Phase Induction Motor
        Construction and Components
        Principle of Operation
        Torque
        Speed Control
        Connections

Induction Motor

      Induction motors are used worldwide in many residential, commercial, industrial, and utility applications.
          Induction Motors transform electrical energy into mechanical energy.
     It can be part of a pump or fan, or connected to some other form of mechanical equipment such as a winder, conveyor, or mixer.





Construction

          The three basic parts of an AC motor are the rotor, stator, and enclosure.
          The stator and the rotor are electrical circuits that perform as electromagnets.


Squirrel Cage Rotor


Construction (Stator construction)



              The stator is the stationary electrical part of the motor.
          The stator core of a National Electrical Manufacturers Association (NEMA) motor is made up of several hundred thin laminations.
          Stator laminations are stacked together forming a hollow cylinder. Coils of insulated wire are inserted into slots of the stator core.
          Electromagnetism is the principle behind motor operation. Each grouping of coils, together with the steel core it surrounds, form an electromagnet. The stator windings are connected directly to the power source.



Construction (Rotor construction)

          The rotor is the rotating part of the electromagnetic circuit.
          It can be found in two types:
        Squirrel cage
        Wound rotor
          However, the most common type of rotor is the “squirrel cage” rotor.

 Construction (Rotor construction)
          Induction motor types:
v                  Squirrel cage type:
Ø  Rotor winding is composed of copper bars embedded in the rotor slots and shorted at both end by end rings
Ø  Simple, low cost, robust, low maintenance
v   Wound rotor type:
Ø  Rotor winding is wound by wires. The winding terminals can be connected to external circuits through slip rings and brushes.
Ø  Easy to control speed, more expensive.

Construction (Rotor construction)

Wound Rotor

Squirrel-Cage Rotor


Construction (Enclosure)

          The enclosure consists of a frame (or yoke) and two end brackets (or bearing housings). The stator is mounted inside the frame. The rotor fits inside the stator with a slight air gap separating it from the stator. There is NO direct physical connection between the rotor and the stator.


          The enclosure also protects the electrical and operating parts of the motor from harmful effects of the environment in which the motor operates. Bearings, mounted on the shaft, support the rotor and allow it to turn. A fan, also mounted on the shaft, is used on the motor shown below for cooling.

Construction (Enclosure)


Nameplate Data


Manufacturer’s Type


Manufacturer’s Type


Rated Voltage

FLA(Full Load Amps)
Rated Frequency
Full Load RPM
Insulation Class
Ambient Temperature
Time Rating(Duty)
Horsepower Rating
Locked Rotor kVA Code

Power Factor
Service Factor
Enclosure Type
Nominal Efficiency
Frame Size
NEMA Design Letters

Rotating Magnetic Field
          When a 3 phase stator winding is connected to a 3 phase voltage supply, 3 phase current will flow in the windings, which also will induced 3 phase flux in the stator.
          These flux will rotate at a speed called a Synchronous Speed, ns. The flux is called as Rotating magnetic Field
          Synchronous speed: speed of rotating flux


          Where;                 p = is the number of poles, and
                                                f  = the frequency of supply

AC Machine Stator
 Slip and Rotor Speed

          The synchronous speed for a squirrel cage motor is calculated by multiplying the constant 120 times the electrical supply frequency; then dividing the result by the number of poles in the motor.
Synchronous speed = 120(frequency)
                                        no. of poles

Slip and Rotor Speed


The actual speed of a squirrel cage motor is less than its synchronous speed. This difference between actual speed and synchronous speed is called "slip.“

                                                                slip%= (syn-actual)(100)
                                                                                        sync
Slip and Rotor Speed
The design of a motor stator and rotor affect its slip characteristics. Squirrel cage motors are made with slip ranging from less than 5% to more than 20%. Motors with slip less than 5% are sometimes called normal slip motors. Motors with slips greater than 5% are used for hard to start loads, because of their inherent capability to create more torque.

Advertisement

Asynchronous and Synchronous Motor
In a typical AC motor, a rotating magnetic field is produced in the stator. The speed of this rotating field is called the synchronous speed and is determined only by the frequency of the power supply and the number of poles of the machine. A synchronous motor is one in which the rotor rotates at the same speed as the rotating magnetic field in the stator. An asynchronous motor is one in which the rotor rotates at a speed slower than the synchronous speed.

 Principle of Operation
Ø  When a 3 phase stator winding is connected to a 3 phase voltage supply, 3 phase current will flow in the windings, hence the stator is energized.
Ø  A rotating flux Φ is produced in the air gap. The flux Φ induces a voltage in the rotor winding (like a transformer).
Ø  The induced voltage produces rotor current, if rotor circuit is closed.
Ø  The rotor current interacts with the flux Φ, producing torque. The rotor rotates in the direction of the rotating flux.


8 comments:

  1. Information given are really awesome. It help me to recall the basic and necessary parts. Thank you.......

    ReplyDelete
  2. If you are looking to buy these transformers, you can get in touch with Miracle Electronics who provides efficient and fault-free transformers set at high standards in accordance with international standards for power generation, transmission and distribution.
    SMPS Transformer Manufacturer in India

    ReplyDelete
  3. Thanks for sharing this post.I read your blog such a nice post.

    standard low voltage motor

    ReplyDelete
  4. I pay you really special thanks for sharing this informative content.
    3 Phase motor Cambodia

    ReplyDelete
  5. Your Blog is very interesting & informative to read. Thanks for Sharing the information about single phase & 3 pahse induction motor!. MM ENGINEERING SERVICES LTD is the only one who delivers the quality products as they promised to their customers.

    ReplyDelete
  6. Great post thanks for the sharing!!! but If you want to buy any petroleum Equipment, Petrodirect has a best 12 Volt Fuel Transfer Pump

    ReplyDelete
  7. Thank you for your informative post!!!
    Village Talkies a top-quality professional corporate video production company in Bangalore and also best explainer video company in Bangalore & animation video makers in Bangalore, Chennai, India & Maryland, Baltimore, USA provides Corporate & Brand films, Promotional, Marketing videos & Training videos, Product demo videos, Employee videos, Product video explainers, eLearning videos, 2d Animation, 3d Animation, Motion Graphics, Whiteboard Explainer videos Client Testimonial Videos, Video Presentation and more for all start-ups, industries, and corporate companies. From scripting to corporate video production services, explainer & 3d, 2d animation video production , our solutions are customized to your budget, timeline, and to meet the company goals and objectives.
    As a best video production company in Bangalore, we produce quality and creative videos to our clients.

    ReplyDelete
  8. Your post has reminded me of the importance of regular maintenance for single-phase motors. Preventative measures can save me money and ensure optimal functionality. Thank you for the helpful reminder!

    ReplyDelete