Skip to main content

Synchronous motor - Detailed Description I

Synchronous motor vs Induction motor:
In AC motor there are two types:
  1. Synchronous motor
  2. Asynchronous motor or Induction motor
Lets see the main difference between synchronous and Asynchronous motor:

1. In construction wise:
Synchronous motor has stator wounded on winding for specific number of poles and a salient pole rotor which is energized by DC supplysimilar to that of synchronous motor but the rotor may be short circuited squirrel cage or changing slip ring

2. In Speed wise:
As we know Synchronous motor always runs at Synchronous speed where as Induction motor runs at speed less than\n synchronous speed
Synchronous speed: N =Ns
Induction motor speed: N<Ns 

3. In working principle wise:
Synchronous motor principle is magnetic locking, where as Induction motor principle is Relative Magnetic Field (RMF) as it is based on Lenz law

4. In power factor wise:
Synchronous motor has the ability to operate in leading, lagging and unity where as Induction motor always runs in lagging

5. In maintenance wise:
Induction motor will have brushes and slip rings where as synchronous motor is free from all those cost

6. In efficiency wise:
Synchronous motor will have high efficiency compared to Induction motor because of synchronous speed

7. In cost wise:
Synchronous motor cost is higher than Induction motor cost

What is synchronous motor:
Synchronous motor is an AC motor in which at steady state rotation of shaft is synchronized with the frequency of the supply current.
It's rotating period is integral number of AC cycles

Synchronous motor construction:
As like other motor synchronous motor also has stator and rotor

Stator :Synchronous motor construction is similar to the other motor where the stator is wounded on winding s for a specific number of poles. Stator is laminated with silicon to reduce hysteresis and Eddy current losses

Rotor: Rotor is salient type. The rotor windings are connected to DC power supply through slip rings
Always thenumber of
poles of stator = poles of rotor
Synchronous motor construction

Working Principle:

The 3 phase supply is given to the stator as soon as the supply is given stator starts to rotate at Synchronous speed to produce a rotating magnetic field in the clockwise direction. When the DC supply is given to rotor it gets magnetized and produce rotating magnetic field.
Now the north poles of stator starts attracting north poles of rotor and the south poles of stator starts attracting south poles of rotor. As like poles repels each other the torque starts to rotate in anticlockwise direction. At this condition the motor won't run.
To avoid such condition the rotor is also rotated upto synchronous speed using DC supply. So the stator can skip the same pole in time difference. Now the two opposite fields will attract each other. Both stator and rotor rotates at same speed this is called as magnetic locking.

Magnetic locking

Do synchronous motor operate as synchronous generator:
The synchronous motor can operate as synchronous generator as they are same in construction by giving mechanical input. when we give mechanical input using turbine then rotor can rotate and as per principle of electromagnetic induction we will get voltage across stator winding having frequency dependent on speed of rotor

Comments

Popular posts from this blog

Center Tapped Transformer

Center Tap: Center Tap is a point connected along the half way of transformer, inductor, resistor or potentiometer. It provides variable in the value. Center Tapped transformer: Mostly center tapped transformer are used to reduce low voltage supply. This happens when the demand is more than the supply voltage. If the transformer is overloaded then the output voltage reduces. This problem can be reduced by using Center tapped transformer where the number of turns can be changed by connecting at various point of windings. so the output voltage can be managed. Center tapped transfromer has the same working principle as normal transformer but the main difference is secondary winding is divided into two parts. Center tapped transformer Working Principle:  The working principle is same as normal transformer. If the alternating current is made to pass through the primary winding the flux will be produced in it, when the secondary winding is brought near to it, an induced e...

EEE Interview Questions IV

1. What is Power System? It is a branch of electrical engineering which deals with the study of generation, transmission, distribution and utilization of electrical energy 2. What is Power Factor? The cosine of angle between voltage and the current in an AC circuit is known as power factor 3. How should be power factor for the good working system? Power Factor should be less than 1 for the good working system 4. What is one line diagram? One line diagram is a single line representation of  three phase power system It consists of symbol representation of  bus bar, Generator, Alternator, e.t.c [caption id="attachment_91" align="alignnone" width="624"]                                                                one line diagram 5. W...

Basic MCQ's of EEE-I

1.What is the unit of electrical charge? 1.watt 2. joule 3. volt  4. coulomb   Answer: 4 Explanation: unit of Charge -> Coulomb, Energy ->Joule, Voltage -> Volts, Power -> Watts 2 . The minimum resistance value for a blue, gray, red, silver resistor is 1. 612  2. 6,120 3. 6,800  4. 6,460  Answer: 2 Explanation: blue-6 grey-8 red-2 so value is 6800ohms tolerance +-10% therefore minimum resistance value is 6800/100*10=680 6800-680=6120 3 . If the current changes from 4A to 5A in 1s with the emf 10V. then what will be the value of inductance?  1.10H  2. 20H  3. 30H  4. 40H  Answer: 1  Explanation: As emf=L(i2-i1)/t by substituting i2=4A, i1=5A, emf=10V,we get L=10H 4. What happens when many resistors are connected in series? 1. Divides the voltage proportionally 2. Divides the current propotionally 3. Increase the source voltage 4. Decrease the power to zero ...