Alternator Interview Questions & Answers

Question 1. What Is Meant By Synchronising The Alternators?

Answer :

The process of connecting two or more alternators in parallel for supplying a common load is called synchronising.

Question 2. What Are The Conditions To Be Satisfied For Proper Synchronising Of Alternators?

Answer :

1. The terminal voltage of the incoming alternator must be the same as bus-bar voltage.
2. The speed of the incoming alternator must be such that its frequency equals to the bus-bar frequency
3. The phase sequence of the incoming alternator must be the same as that of the other alternators or busbars.

Question 3. What Are The Advantages Of Parallel Operation Of Alternators?

Answer :

1. It ensures continuity of power supply to consumers in case of breakdown of an alternator in an generation station.
2. This is economical and improves the efficiency of the generating station.
3. When the demand of power increases, new alternators can be installed to operate in parallel.
4. It is not possible to built single large size alternator to meet the requirement.

Question 4. What Are Types Of Rotors Used In Alternators?

Answer :

There are two types of rotors used in alternators namely

1. Salient pole rotor
2. Smooth cylindrical type rotor

Question 5. What Are The Advantages Of Providing Damper Winding?

Answer :

The damper winding is useful in preventing the hunting ( momentary speed fluctuations) in generators.

The damper winding also used to maintain balanced 3 phase voltage under unbalanced load conditions.

Question 6. What Are The Various Methods To Determine The Voltage Regulation Of The Large Alternators?

Answer :

In case of small machines, the regulation can be found by direct loading.

For large alternators, to find the voltage regulation indirect methods are used. They are

1. Synchronous Impedance Method.
2. The Ampere-turn method.
3. Zero power factor or Pointer Method.

Question 7. What Is The Basic Principle Of Alternators?

Answer :

Alternators is noting but a AC generators. They operate on the fundamental principle of electromagnetic induction as dc generators.

ie, when the rotor rotates, the emf is induced in the stator.

Question 8. Which Type Of Rotor Is Suitable For Low Speed Alternators? Salient Pole Type Or Cylindrical Type Rotor?

Answer :

Salient pole type alternators are suitable for low and medium speed alternators. It has large number of projecting poles. It has large diameters and short axial lengths.

Question 9. What Is Meant By Turbo Alternators?

Answer :

High speed alternators are called as Turbo alternators.

As it runs at very high speed, salient pole rotors are not used. Smooth cylindrical type rotor is suitable for turbo alternators.

Question 10. What Are The Two Types Of Turbo-alternators ?

Answer :

Vertical and horizontal.

Question 11. How Do You Compare The Two ?

Answer :

Vertical type requires less floor space and while step bearing is necessary to carry the weight of the moving element, there is very little friction in the main bearings.

The horizontal type requires no step bearing, but occupies more space.

Question 12. What Is Step Bearing ?

Answer :

It consists of two cylindrical cast iron plates which bear upon each other and have a central recess between them. Suitable oil is pumped into this recess under considerable pressure.

Question 13. What Is Direct-connected Alternator ?

Answer :

One in which the alternator and engine are directly connected. In other words, there is no intermediate gearing such as belt, chain etc. between the driving engine and alternator.

Question 14. What Is The Difference Between Direct-connected And Direct-coupled Units ?

Answer :

In the former, alternator and driving engine are directly and permanently connected. In the latter case, engine and alternator are each complete in itself and are connected by some device such as friction clutch, jaw clutch or shaft coupling.

Question 15. Can A D.c. Generator Be Converted Into An Alternator ? If Yes Then How ?

Answer :

Yes. A DC generator can be converted into an alternator. By providing two collector rings on one end of the armature and connecting these two rings to two points in the armature winding 180° apart.

Question 16. Would This Arrangement Result In A Desirable Alternator ?

Answer :

No.

Question 17. How Is A Direct-connected Exciter Arranged In An Alternator ?

Answer :

The armature of the exciter is mounted on the shaft of the alternator close to the spider hub. In some cases, it is mounted at a distance sufficient to permit a pedestal and bearing to be placed between the exciter and the hub.

Question 18. Any Advantage Of A Direct-connected Exciter ?

Answer :

Yes, economy of space.

Question 19. Will Installing The Quicktifier 210 On My 105 Amp Gm Alternator Get Me More Power?

Answer :

The main function of the Quicktifier is to add durability. You will get a bit more power but not that much. The Quicktifier should only be used when the alternator has enough power but it doesn't hold up.

Question 20. What Is The Difference In Connection Batteries In Parallel Or Series?

Answer :

When you connect batteries in parallel you connect positive to positive and negative to negative. With a parallel connection you are increasing the size of the pool of power you have but the voltage stays the same as the original batteries. To connect in series you connect positive to negative then you get one positive from one battery and the negative from the other battery. When you connect two batteries in series it adds the voltage up. So if you have two 12 volt batteries and connect them in series you will end up with 24 volts.

Question 21. What Is The Bridge Rectifier In An Alternator And What Does It Do?

Answer :

Every Auto, Truck, Farm, Industrial, Marine Alternator has inside it what is called a Bridge Rectifier. The Bridge Rectifier is the assembly in every alternator that converts the AC (alternating current) that alternators make to DC (direct current) for use by the vehicles battery & electrical system. The Bridge Rectifier converts AC to DC using diodes which are semiconductors that are one way gates. Diodes allow current to flow in only one direction making alternating current into direct current.

One very important note when it comes to high output alternators and bridge rectifiers. When you upgrade the output of your alternator you must also upgrade the diodes in the bridge rectifier to a higher amperage rating. Example: If you have a 100 amp alternator with a 110 amp rated bridge rectifier and then you upgrade the alternator to 200 amps but you still have the 110 amp rated bridge rectifier, it won't last long. We use Heavy Duty Single, Dual and Triple Internal and External Bridge Rectifiers to increase the durability and prevent High Output Alternator failure.

Question 22. What Size Is The 70's Gm Alternator Pulley Nut?

Answer :

The older Delco 10DN, 10Si, and 12Si (and 15Si through DR44G) series alternators have a 17mm pulley shaft and a very odd sized nut. It looks like an M17 metric thread, but it is actually an imperial decimal thread, .668-20.

Question 23. What High Output Alternators Are Available For The 2007 Shelby Gt500?

Answer :

The 2007 Shelby GT500 uses the Ford Motorcraft 6G series alternator. The 6G comes in a small case 110 amp version and also a large case 130 amp. The mounting for the small case and large are the same on the '07 GT500, but not all small case units have a large case match.

We can boost the output on both the small and large case 6G, but the large case is better. The larger case dissipates the extra heat from the higher output and also puts out more power at idle because of the larger diameter.

The large case is available in 140, 160, 200 & 250 amp versions. The 250 amp requires the addition of the Quicktifier External Dual or Triple Bridge Rectifier.

Question 24. What Is The General System Requirements Of Alternator?

Answer :

For the generation of emf, there should be two basic systems.

1. magnetic field system to produce the magnetic field
2. Armature system which houses the conductors on which the EMF is to be induced.

Question 25. Will The Alternators Have Rotating Armature System Or Stationary Armature System?

Answer :

Generally in alternators, the armature is stationary and the field rotates. Small lowvoltage alternators often have a rotating armature and a stationary field winding.But in large alternators rotating armature field type is used.

Question 26. What Are The Advantages Of Stationary Armature And Rotating Field System?

Answer :

1. The stationary armature coils can be insulated easily.
2. Higher peripheral speed can be achieved in the rotor.
3. Cooling of the winding is more efficient.
4. Only two slip rings are required to give DC supply to the field system
5. Output current can be easily supplied to the load circuit. Sliprings and brushes are not necessary.

Question 27. 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 known as rotor.

Question 28. What Are The Advantages Of Three Phase Motor Over Single Phase Motor?

Answer :

Three phase motors are having:

1. Higher starting torques
2. Improved speed regulation
3. Less vibration
4. Quieter operation

compared to the single phase motors.

Question 29. What Is Basic Principle Of Operation Of Alternators/dc Generators?

Answer :

They are working on the fundamental principle based on Faraday’s Laws of Electromagnetic Induction.

This law states that, When a current carrying conductor moves in magnetic field, it induces an EMF.

Question 30. How To Minimize The Eddy Current Losses?

Answer :

When the core is laminated and insulated from each other with paper or varnish the eddy current loss is minimized.

Question 31. What Are The Various Types Of Rotors Used In The Alternators?

Answer :

1. Salient pole rotor
2. Nonsalient pole rotor or Cylindrical rotor

Question 32. Define Pole Pitch?

Answer :

The distance between the centres of two adjacent poles is called pole pitch. One pole pitch is equals to 180 electrical degrees. It is also defined as the number of slots per pole.

Question 33. Define Coil Span.?

Answer :

The distance between the two coil sides of a coil is called as coil span. It may be expressed in electrical degrees or in number of slots.

Question 34. What Is Meant By Full Pitched Winding?

Answer :

If the coil span is equal to pole pitch, the winding is called as full pitched winding.

Question 35. What Is Meant By Short Pitched Winding?

Answer :

If the coil span is less than the pole pitch, the winding is called as shotpitched winding. It is also known as shortchorded winding.

Question 36. What Are The Advantages And Disadvantages Of Shortpitched Winding?

Answer :

The advantages are:

1. They save copper for end connections
2. They improve the waveform of the generated EMF.
3. The generated EMF can be made to approximate to a sine wave more easily and the distorting harmonics can be reduced.

The disadvantages are:

1. The total voltage around the coils is some what reduced. Because the voltage induced in the two coil sides are slightly out of phase.