etpmm

Electrical Technology, Politeknik Merlimau

CONCLUSION

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  1. The three AC MOTOR TYPES presented are the series, synchronous, and induction ac motors.
  2.  SYNCHRONOUS MOTORS are specifically designed to maintain constant speed, with the rotor synchronous to the rotating field. Synchronous motors require modification (such as squirrel-cage windings) to be self-starting.
  3. INDUCTION MOTORS are the most commonly used of all electric motors due to their simplicity and low cost. Induction motors may be single-phase or multiphase.
  4. SYNCHRONOUS SPEED is the speed of stator field rotation. It is determined by the number of poles and the frequency of the input voltage.
  5. SLIP is the difference between actual rotor speed and the synchronous speed in induction motors. Slip must exist for there to be torque at the rotor shaft.

Written by -Aizura-

July 7, 2011 at 10:24 PM

Posted in Chapter 6

6.4 AC MOTOR STARTER

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  • Function: used to enable the motor to work safely when first turned on until stopped again.
  • Functions of  ac motor starter
    • Start the motor
    • Control the speed
    •  Stop the motor
    •  Reversing the direction of motor rotation
    •  Stop the motor when the motor overload and heat
  • The types of ac motor starter
    •  star-delta starters
    • rotor resistor starter
    • auto-transformer starter

Written by -Aizura-

July 7, 2011 at 10:23 PM

Posted in Chapter 6

Activity & Feedback 6C

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ACTIVITY 6C

If three phase induction motor has 6 poles and operates with the supply of 220V, 50­­­Hz source with the slip of 4%, determine the values of synchronous speed, armature (rotor) speed and the frequency of rotor currents.

FEEDBACK 6C

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Written by -Aizura-

July 7, 2011 at 10:17 PM

6.3 SYNCHRONOUS SPEED, ROTOR SPEED AND SLIP

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  1. Synchronous speed
    • Speed ​​of rotating magnetic field in the stator
    • The synchronous speed is determined by the following equation:
  2. Rotor speed
    • Armature rotational speed of induction motors; Formula : Nr = Ns(1-s)
  3. Slip
    • The difference between synchronous speed of the rotor speed

Written by -Aizura-

July 7, 2011 at 10:08 PM

Posted in Chapter 6

Activiti & Feedback 6B

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ACTIVITY 6B

  1. What are the three basic types of AC motors?
  2. The AC induction motor has three basic parts : the ……….., which is the stationary part  of the motor ; the ……………, which is the rotating part of the motor and the ………….., which house the bearings that allow the rotor to rotate freely.
  3. What is the advantage of AC motor over DC motor?

FEEDBACK 6B

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  1. Series, synchronous, induction.
  2. Stator, rotor, end plates.
  3. The AC motor provides several advantages over DC motors. One advantage the AC    motor has is its design eliminates the need for brushes and commutators. The second advantage is that its rotating member is made of laminated steel rather than wire that is pressed on a core, which reduces maintenance.

Written by -Aizura-

July 7, 2011 at 9:51 PM

6.2.4 Differences between AC Motor and DC motor

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AC Motor

DC motor

have high starting power built transmit lower levels of overall power

not be as good at producing power over long lengths

widely used in industrial applications

limited use in industrial applications

Rotor – laminated steel allows AC motor to operate longer than DC

Rotor – copper coils pressed on a laminated steel core

speed could be controlled more easily with frequency

speed could be controlled

less maintenance since it does not have brushes

High maintainance since it still use brushes

Written by -Aizura-

July 7, 2011 at 9:43 PM

Posted in Chapter 6

6.2.3.3 Three – Phase AC Motors

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  • Three-phase AC motors are known as the ‘workhorses of industry’ because of their wide use and acceptance
  •  They are popular because they are low in cost, compact in size, require less maintenance, withstand harsh industrial environments, etc.
  • Three-phase AC motors are a class of motors that convert the three-phase electric power supplied at the input terminals, to mechanical power at the rotating shaft, through the action of a rotating magnetic field, produced by a distributed winding on the stator
  • The three phases of AC motors are:-
    1. Induction motor
      • No voltage is applied to the rotor
      • The voltage is applied to the stator winding
      • When the current flows in the stator winding, a current is induced in the rotor by transformer action
      • The resulting rotor magnetic field will interact with the stator magnetic field, causing torque to exert on the rotor
    2. Synchronous motor
      • Rotor speed remains in synchronism with that of the stator magnetic field
      • The motor runs at the same speed. Unlike induction motors, synchronous motors are not self-starting
      • They have to be brought up to synchronous speed. Once they are locked then the rotor will continuously rotate
    3. Wound rotor induction motor
      • This motor has a ‘wire wound rotor’ from which three leads are brought out to the slip rings
      • It is possible to vary the rotor resistance
VIDEO 5 - 3PHASE animation
VIDEO 5 – 3 Phase Animation


Written by -Aizura-

July 7, 2011 at 9:38 PM

Posted in Chapter 6

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