Electrical Machines Interview Questions And Answers
Question: 1. What Is The General System Requirements Of Alternator?
Answer:
For the technology of emf, there have to be two simple structures.
Magnetic subject system to produce the magnetic field
Armature system which homes the conductors on which the EMF is to be prompted.
Question: 2. Will The Alternators Have Rotating Armature System Or Stationary Armature System?
Answer:
Generally in alternators, the armature is desk bound and the sphere rotates. Small low-voltage alternators regularly have a rotating armature and a stationary area winding.But in massive alternators rotating armature area type is used.
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Question: 3. What Are The Advantages Of Stationary Armature And Rotating Field System?
Answer:
The desk bound armature coils may be insulated without difficulty.
Higher peripheral speed may be achieved within the rotor.
Cooling of the winding is greater efficient.
Only slip jewelry are required to give DC supply to the sphere machine
Output modern can be easily furnished to the load circuit. Slip-earrings and brushes are not necessary.
Question: 4. What Is Meant By Stator? What Is Meant By Rotor?
Answer:
In any electrical machine ( AC/DC motor or generator) the stationary member is called as stator. Similarly in all machines the rotating member is called rotor.
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Question: 5. What Are The Advantages Of Three Phase Motor Over Single Phase Motor?
Answer:
Three phase automobiles are having
Higher starting torques
Improved speed regulation
Less vibration
Quieter operation
compared to the single section motors.
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Question: 6. What Is Basic Principle Of Operation Of Alternators/dc Generators?
Answer:
They are working at the fundamental principle based on Faraday’s Laws of Electromagnetic Induction.
This regulation states that, When a modern sporting conductor moves in magnetic discipline, it induces an EMF.
Question: 7. How To Minimize The Eddy Current Losses?
Answer:
When the center is laminated and insulated from each other with paper or varnish the eddy cutting-edge loss is minimized.
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Question: eight. What Is Meant By Turbo Alternators?
Answer:
Turbo alternators are high pace alternators. Because of excessive speed of rotation, the rotor diameter is decreased and the axial duration is improved. Two or 4 poles are commonly used and steam mills are used as high movers.
Question: nine. What Are The Various Types Of Rotors Used In The Alternators?
Answer:
Salient pole rotor
Non- salient pole rotor and Cylindrical rotor
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Question: 10. Define Pole Pitch?
Answer:
The distance between the centres of adjoining poles is called pole pitch. One pole pitch is equals to one hundred eighty electrical tiers. It is likewise defined as the quantity of slots per pole.
Question: eleven. Define Coil Span?
Answer:
The distance among the 2 coil aspects of a coil is called as coil span. It can be expressed in electric stages or in wide variety of slots.
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Question: 12. What Is Meant By Full Pitched Winding?
Answer:
If the coil span is same to pole pitch, the winding is referred to as as complete pitched winding.
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Question: 13. What Is Meant By Short Pitched Winding?
Answer:
If the coil span is less than the pole pitch, the winding is known as as shot-pitched winding. It is also called brief-chorded winding.
Question: 14. What Are The Advantages And Disadvantages Of Short-pitched Winding?
Answer:
The advantages are:
They save copper for end connections
They improve the waveform of the generated EMF.
The generated EMF may be made to approximate to a sine wave more easily and the distorting harmonics can be decreased.
The negative aspects are:
The overall voltage around the coils is a few what decreased. Because the voltage brought on in the coil sides are barely out of segment.
Question: 15. Why Is The Efficiency Of A Three-section Induction Motor Is Less Than That Of A Three-section Transformer?
Answer:
Three segment Induction motor is not anything however a rotating transformer.
Due to rotating nature, there are friction and windage losses associated with it.
On the alternative hand, the three-section transformer is a static device, thus there are not any rotational losses.
Thus the efficiency of three-phase induction motor is less than that of a 3-phase transformer.
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Question: 16. Why The Air Gap Between The Pole Pieces And The Armature Is Kept Very Small?
Answer:
The air gap between the pole pieces and the armature is saved very small to preserve the sphere power at its highest fee.
This is due to the purpose the flux traces can skip thru iron very easily than the air gap.
The small air gap generates excessive voltage.
Larger the air hole means stronger should be the magnetising force to produce the required voltage subsequently the air gap is kept very small.
Question: 17. Why Does Curving The Pole Faces In A Dc Machines Contributes To A Smoother Dc Output Voltage From It?
Answer:
For having smoother output voltage from DC machines its commutation need to be as perfect as viable.
In order to have proper commutation the flux density within the air hole have to decrease regularly from most fee under the centre of the pole to 0 on.
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Question: 18. The Series Field Winding Has Low Resistance While The Stunt Field Winding Has High Resistance. Why?
Answer:
The collection filed winding is usually related in series with the armature and for this reason has to hold the armature present day which without delay gets decided by using the burden.
Thus the current passing via series field winding is of high degree.
The voltage drop across series discipline winding receives introduced to the voltage drop throughout armature winding while determining the returned emf. This voltage drop must be very small.
Hence as the contemporary via series field winding is high, if you want to keep voltage drop across it to a small price, its resistance is very low.
On the other hand, the shunt area winding is directly connected throughout the rated supply voltage for this reason to restrict cutting-edge via it, resistance is very excessive.
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Question: 19. What Are The Conditions To Be Satisfied For Parallel Operation Of Dc Generators?
Answer:
The polarities of the turbines should be same or the connections ought to be interchanged until they end up equal.
The voltages of each the generators have to be same.
The trade of voltage with alternate of load have to be of same character.
The high movers riding the generators have to have strong and similar rotational velocity characteristics.
The positive and negative terminals of mills have to be connected nicely to the effective and poor of busbar.
Question: 20. What Are The Major Parts Of The Dc Generators?
Answer:
Yoke Poles
Field winding
Armature
Armature winding
Commutator brushes
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Question: 21. What Is A Commutator?
Answer:
The commutator is a tool which converts alternating triggered emf in a generator to DC emf. In case of motor it produces unidirectional torque.
Question: 22. What Is Meant By Reactance Voltage?
Answer:
An armature coil has sure self inductance.
When coil undergoes commutation, there’s exchange in current (di) in that coil and the commutation takes sure time(dt).
Thus there’s self-prompted emf in a coil undergoing commutation given by L(di/dt).
This EMF induced inside the coil undergoing commutation is known as reactance voltage.
Question: 23. What Is Electric Motors?
Answer:
An electric powered motor is an electrochemical tool that converts electrical strength into mechanical power. Most electric motors perform through the interaction of magnetic discipline and contemporary carrying conductors to generate pressure.
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Question: 24. On What Principle Electric Motor Works?
Answer:
The Motor Principle: when a current-carrying conductor is located in an external magnetic area perpendicular to the conductor, the conductor experiences a force perpendicular to itself and to the outside magnetic field.The physical precept at the back of production of mechanical pressure by means of the interactions of an electric present day and a magnetic field.
The right-hand rule for pressure on a conductor can be used to determine the path of the force experienced at the conductor.
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Question: 25. How Many Types Of Electric Motors Are There?
Answer:
Mainly there are two kinds of electric cars:
AC automobiles
DC automobiles
Question: 26. What Is Ac Motor?
Answer:
An AC motor is an electric motor driven via an alternating cutting-edge (AC). It generally consists of two simple parts, an outside stationary stator having coils furnished with alternating modern-day to provide a rotating magnetic field, and an interior rotor connected to the output shaft that is given a torque by means of the rotating subject.
Question: 27. What Is Dc Motors?
Answer:
A DC motor is a mechanically commutated electric motor powered from direct present day (DC). The stator is desk bound in area by using definition and therefore so is its present day. The contemporary in the rotor is switched by the commutator to also be stationary in area. This is how the relative angle between the stator and rotor magnetic flux is maintained near ninety ranges, which generates the maximum torque.
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Question: 28. What Are The Applications Of Electric Motor?
Answer:
Electric automobiles packages are: commercial enthusiasts, blowers and pumps, machine tools, family home equipment, strength equipment, and disk drives, document players.
Question: 29. What Is Universal Motor?
Answer:
A series-wound motor is referred to as a regular motor when it has been designed to function on both AC or DC energy. It operate properly on AC because the contemporary in each the sphere and the armature (and therefore the resultant magnetic fields) will exchange in synchronism and therefore, the resulting mechanical force will occur in a constant course of rotation.
Question: 30. What Are The Advantages And Disadvantages Of Ac, Dc Motors?
Answer:
Advantages of AC Motors:
Low fee,
long life,
excessive efficiency,
big scores to be had (to 1 MW or greater),
big quantity of standardized sorts.
Disadvantages of AC Motors:
Starting inrush contemporary can be high,
pace manage requires variable frequency supply.
Advantages of DC Motors:
Precision positioning,
High preserving torque,
Long lifespan,
Low preservation,
High performance
Disadvantages of DC Motors:
Some may be high-priced,
Require a controller,
Higher initial price,
Requires a controller.