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Participant

Join Date: Aug 2009
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# Exciter Function in Three-Phase AC Generator

08/05/2009 3:14 PM

I would like to know the function of exciter in 3-phase AC generator. As far that i know its gives the starting torque to the generator which helps in pre acceleration of the generator. Is there other function of exciter in the generator? A detail circuit diagram will help too. tq

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Power-User

Join Date: Dec 2007
Location: Sydney Australia
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#1

### Re: Exciter Function in Three-Phase AC Generator

08/05/2009 7:43 PM

The Exciter Function is to provide a Magnetic Field through which conductors may be rotated to generate a voltage and thus allow a current to flow.

Regards,
Sapper

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#2

### Re: Exciter Function in Three-Phase AC Generator

08/06/2009 1:44 AM

Do you mean Generator or Motor ?

Do you mean Exciter Circuit or starting means ?

If it is Exciter and generator then the previous post is correct. It creates and maintains the Magnetic field and its strength so that the necessary energy converson takes place.

If it is Starting of Synchr Motor (In induction mode) then what you said is OK.

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Guru

Join Date: Sep 2006
Location: NSW Australia
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#3

### Re: Exciter Function in Three-Phase AC Generator

08/06/2009 9:08 AM

The function of an exciter in a 3 phase AC alternator is to provide power to the rotating field ,this field cuts the windings of the stator which produces your 3phase output. The output of this exciter can be varied manually or automatically depending on the alternator function.This type of exciter in the form of a DC generator can be mounted on the end of the alternator and is usually self exciting. This method can also be used on DC generators to feed the stator field coils. It douse not give any starting tourque to the alternater unless it is speacialy wound to act as a starter come generator.

Other types of exciters have their windings incorperated in the stator windings the output of these exciter windings are rectified and fead to the rotor, in this case the output of these windings are usualy regulated automaticaly so the alternator output is stabilised. Some of these types are self exciting others require a DC supply from a battery to start up the system

There are hundreds of variations so would suggest you google up any of the above for circuit information.

Garth

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Join Date: Feb 2009
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#4

### Re: Exciter Function in Three-Phase AC Generator

08/06/2009 8:48 PM

Haq,

Are you asking for the initial excitation of generator?

The generator is first speeded up to its rated speed by the prime mover (Engine or Turbine), then it needs the initial excitation to build up the voltage. With initial excitation, an outside DC voltage pulse is directly applied to the exciter (Self-Brushless) field to generate the A.C voltage in its rotating armature. The AC voltage is converted to DC (with diode) which is then supplied to the generator rotating field to build up the voltage in the generator armature, which is the generator terminal voltage. Once the generator terminal voltage is built up, the exciter field current is controlled by the AVR.

The self-brushless exciter is a mini generator installed in the same rotating shaft – the basic difference is its field is stationary, its armature rotates and its frequency is higher.

This link may be of more help:

http://www.kilowattclassroom.com/Archive/SyncMotors.pdf

-MS

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#6

### Re: Exciter Function in Three-Phase AC Generator

08/19/2009 10:48 AM

GA for the best answer up to now when reading down from the top.

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#5

### Re: Exciter Function in Three-Phase AC Generator

08/11/2009 11:57 AM

This sounds like homework and I think you should have gone to class that day. The "as far as I know" that you provided is so far off target I do not know where to start. What is "pre acceleration" anyway? Since when does a generator need "starting torque"? I do not think any circuit diagram, let alone one with detail will help you. Go read a book.

Guru

Join Date: May 2008
Posts: 1812
#7

### Re: Exciter Function in Three-Phase AC Generator

08/25/2012 4:49 AM

Dear Mr. haq,

Starting Torque phenomena is applicable only for motor(s) - be it A.C or D.C Motor.

Exciter will circulate D.C current in the Rotating Field to provide Magnetic Flux, which will produce Voltage in the Windings of the stator. Pre-Acceleration does not arise in this matter.

DHAYANANDHAN.S

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