What is motor (मोटर क्या है) Read for Interview
Motor
Motor is an electrical device which generates /produce an machenical action on the application of electrical control signal.
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| AC motor |
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| DC motor |
Type of Motor
1.AC motor . (which runs on AC supply) 2.DC motor . (which runs on DC supply)
1.AC motor
It has two parts
* Stater part ----static part /stationary part. Stationary pole winding
*Rotor part -----Rotating part /Dynamic part. Rotor-- conductor .
2.DC Motor
The electric motor is a machine which converts electrical energy into mechanical energy.
It has two parts
*stater part ----stater part, solid poles .
*Roter part ----rotating part, armature winding (winding on conductor) .
Working principle ----
When a current carrying conductor is placed in a magnetic field, It's experiences a force whose action is given by flamings Left hand rules. "
🇫〓BILSinӨ (Newton's)
* V = Eb+IaRa (motor)
* Eg=V +IaRa (Genrator)
* V = applied voltage
* Be = back or counter e. m. f. developed in the armature of the motor.
* Eg = Genrator e. m. f. developed in the generator armature.
* IaRa = Armature voltage drop due to a flow of armature current through an armature of given resistance Ra.
Q. What is Induction motor?
Ans . Asynchronous AC motor is Induction motor.
Q. How we can say to 3-phase that it is 3-phase?
Ans. All Line have 120 equal phase difference. It is said 3-phase supply 3-phase has 440 AC supply .
Working operation --
Asynchronous type squarrel cage motor is known as induction motor. It works on Induction principle. It consists of a stator part, Rotor part and a shaft. The shaft is mounted on the rotor. Shaft is responsible to attach the load with the motor.
In induction motor when the 3-phase supply is applied to the stator a revolving flux is developed inside the stator. This revolving field or flux get cut by rotor. As per the Faraday's law of electromagnetic induction an induced emf generates an induced current in the conductors. As per the Lenz Law an induced current opposes the emf which has produced it. This apposing force slesh rotating force also know as torque, tends to rotate the rotor and the shaft which is bounded on the rotor also rotates.
The speed of the rotor is developed by Nr.
Ns = speed of revolving field /flux.
Nr = rotor speed
Also, Ns = Synchronous speed
Ns = 120f/p (where f=frequency 50 hz)
If , Ns >Nr, slip = +ve (motor)
If, Ns<Nr, slip = -ve (Genrator)
If, Ns =Nr, slip = 0 (Transformer, it is static device)
Torque ----
Rotating force or Turning movement of force is known as Torque.
It is denoted by τ (tau).
τ=F×S (n. m. )
Power----
Rate of doing work. (S. I. Unit watt, kilo watt, Horse power (HP))
1000 watt = 1 kw
786 watt = 1hp
1000 watt = 1.5hp(aprox).
R. P. M. ----
R. P. M. ---- Revolution per minute.
Horse power, HP = Torque × speed (r. p. m.)
[ H. P. = τ྾ѕ]
Power. P = W/T =PI (VA, kva) for power transmission.
P = vi cosΦ (watt, kw, HP) for power Generation.
Power Factor ------
Power factor -- Angle between voltage and current.
CosФ = Real Power / Apprant power
= vi cosΦ÷vi = cosΦ
[E(kwh) = voltage ྾current ྾Time ]
* Ideal power factor = 1
* Good power factor = 8.0
* poor power factor = >8.0 (Less then)
Q. Induction motor takes nearly 6 to 10 times more current in than the normal rated current why?
Ans. Because Induction motor has poor power factor ( voltage, Lagging /current Leading). Once the power factor starts improving, we slowly slowly withdraws current and motor runs on rated speed and current.
Q. Why Induction motor is widely preferred in industries?
Ans. Induction motor Generates nearly two times of torque in starting them normal rated torque. So it is preferred most widely in industries.
Q. How we can reverses the direction of 3-phase induction motor?
Ans. We can reverse the direction of induction motor by Interchange between any of the two phase and Leaving the third one as it is.
Points ----
*commutator converts AC to DC and DC to AC.
*AC motor is cylinder in shape.
*DC motor is rectangular in shape .
*IN DC p & n mean ---- positive & negative.
*IN AC p & n mean ---- phase & nutral .
Note -----
AC motor --
* It's works on AC supply.
*Lamination core.
*Low noise.
*High speed.
*Small size.
* simple construction.
*No speed regulation.
DC motor ----
*Its works on DC supply.
*Pole core is solid but armature core Laminated.
*High noise.
*Low speed.
*Big size.
*Complicated construction.
*speed regulation.
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