Table of Contents
The synchronous motor is a type of AC motor that runs at synchronous speed. The asynchronous motor is a type of AC motor that runs on speed less than the synchronous speed. It operates on the principle of magnetic interlocking between rotor and stator field. it is always less than synchronous speed.
What is difference between synchronous and induction motor?
Synchronous motors require an additional DC power source for energizing rotor winding. Induction motors do not require any additional power source. Synchronous motors require additional starting mechanism to initially rotate the rotor near to the synchronous speed. No starting mechanism is required in induction motors.
What is the meaning of asynchronous motor?
Definition: An electric motor that works with alternating current is known as the asynchronous motor. This motor mainly works on the induced current within the rotor from the rotary magnetic field of the stator. In this motor design, the movement of the rotor cannot be synchronized through the moving stator field.
What is the main disadvantage of synchronous motors?
Disadvantages or Demerits: Synchronous motors requires dc excitation which must be supplied from external sources. Synchronous motors are inherently not self starting motors and needs some arrangement for its starting and synchronizing. The cost per kW output is generally higher than that of induction motors.
Why do we use synchronous motors?
usually, synchronous motors are used for applications where precise and constant speed is required. While used in high power industrial sizes, these motors perform two important functions. One is as an efficient means of converting AC energy into mechanical energy and the other is Power factor correction.
Why synchronous motors are not self-starting?
Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator. Once the rotor nears the synchronous speed, the field winding is excited, and the motor pulls into synchronization.
How does a synchronous motor start?
The motor is first started as a slip ring induction motor. The resistance is gradually cut-off as the motor gains speed. When it achieves near synchronous speed, DC excitation is given to the rotor, and it is pulled into synchronism. Then it starts rotating as a synchronous motor.
How is a synchronous motor controlled?
Synchronous motors are constant speed motors. They run at the synchronous speed of the supply. We can control the speed of the synchronous motor by changing the frequency of the supply to the motor.
What is the use of asynchronous motor?
An asynchronous motor has a passive rotor that is short-circuited permanently (squirrel-cage rotor) or temporarily (see Slip ring rotor). It can produce up to several megawatts and is most frequently used as a standard three-phase motor in industrial applications.
What are the types of asynchronous motor?
Three Phase Asynchronous Motor (Induction Motor) Squirrel Cage Induction Motor. Slip Ring Induction Motor or Wound Rotor Motor.
What is the working principle of asynchronous motor?
The operating principle of an asynchronous motor involves creating an induced current in a conductor when the latter cuts off the lines of force in a magnetic field, hence the name “induction motor”. The combined action of the induced current and the magnetic field exerts a driving force on the motor rotor.
Where do we use synchronous motor?
Synchronous motors are normally used in applications in which a constant and precise speed is required. Typical applications of these low power motors are positioning machines. They are also used in robot actuators. Synchronous motors are also used in ball mills, watches, record players, and turntables.
What are the main characteristics of synchronous motor?
Main Features of Synchronous Motors Synchronous motors are inherently not self starting. The speed of operation of is in synchronism with the supply frequency and hence for constant supply frequency they behave as constant speed motor irrespective of load condition.
What are the main parts of synchronous motor?
The Construction of Synchronous Motors A synchronous motor is generally made up of two parts, a stator the stationary part of the machine that carries the armature winding in which the voltage is generated, and a rotor the rotating part of the machine that produces the main field flux.
Are synchronous motors AC or DC?
In a synchronous motor, AC power is supplied to the stator to generate a rotating magnetic field. DC power is supplied to the rotor which results in discrete North (N) and South (S) poles.
Why the speed of synchronous motor is constant?
When you supply 60 Hz (or 50 Hz), the motor will spin at one speed, which is dependent on the number of poles. This rotational speed will be constant with different mechanical loads, up to the point that the motor (or coupling) fails, hence it is a “constant speed” motor.
Do synchronous motors have slip?
Synchronous motor is a machine whose rotor speed and the speed of the stator magnetic field is equal. Synchronous motor does not have slip. The value of slip is zero. Asynchronous motor has slip therefore the value of slip is not equal to zero.
Are asynchronous motor self-starting?
The current carrying rotor being placed in a magnetic field experiences a torque and hence begins to rotate in the direction of rotating magnetic field. Thus we see that Induction Motor is self-starting. It does not require nay external mean to rotate.
What is synchronous motor speed?
The synchronous speed is the speed of the revolution of the magnetic field in the stator winding of the motor. It is the speed at which the electromotive force is produced by the alternating machine. A machine that runs at synchronous speed is called a synchronous machine.
Which synchronous motor will be smallest in size?
Which synchronous motor will be smallest in size ? (D) 10 HP, 375 rpm. Explanation: Q15.
Which type of starter is used for synchronous motor?
Controllers for synchronous motors have four components: a three-pole starter for the ac stator circuit, a contactor for the dc field circuit, an automatic synchronizing device to control the dc field contactor, and a cage-winding protective relay to open the ac circuit if the motor operates too long without.
How does a 3 φ synchronous motor start?
A three-phase synchronous motor has no starting torque. Once up to speed, the rotor field can be excited with direct current and the rotor is, in effect, then dragged around at the same speed as the three-phase stator field. Its speed is synchronized with that of the stator field.
Why do we give DC excitation to AC synchronous motor?
When AC supply is given to the stator winding or static armature winding of the synchronous motor it creates a rotating magnetic field. If we give DC supply to the field winding or rotor winding of the synchronous motor then the pole created in the rotor will be constant.
