Alternator

Read the manufactures information!

If all else fails, read the instructions.

The basic is that, in any ac generator there should be presence of magnetic lines of force, cutting of magnetic lines of force, before voltage is generated. The exciter is a small dc generator that produced the necessary field to be sent to the main rotor winding and due to the magnetomotive force of main rotor winding and main stator winding voltage is produced.

1. The alternator [AC generator] will run, most likely, at 3000 rev/min [50 turns a second] for 50 Hz, or 3600 rev/min for 60 Hz and have two poles (That means 1 north pole and 1 south pole, which really means the rotor has just one winding).
2. Or it could be half the speed, a 4 pole machine, essentially an X section with two rotor windings at right angles to each other.
3. In the past, direct current was fed to the rotor windings via slip-rings. This makes the rotor a big electromagnet with its axis perpendicular to the shaft axis.
4. Nowadays, "brushless" is usual - that means exciter windings on the rotor pass fixed direct-current field windings on the frame. This produces alternating voltage in the exciter windings on the rotor which is rectified by silicon diodes (on the rotor) to produce direct current which is fed to the main field winding. The exciter alternator frequency is usually several times that of the main output, so that main rotor current is practically ripple-free direct current.
5. There is often a rotor permanent-magnet "pilot exciter", overhung on the non-drive end, the fixed output windings of this give an alternating voltage, typically 240 -400 Hz which is rectified by the Automatic Voltage Regulator (AVR usually a solid - state static box ) in a controlled way to keep the main output at design voltage, despite load current and phase changes. There could be a transformer-rectifier in place of the pilot exciter.
6. Roughly speaking, the main field voltage/ exciter are 200V while the pilot exciter is 250V. The exciter field, driven by the AVR is about 20V DC on-load.
7. The rotor induces the output voltage in the fixed main 3 phase armature.windings around the rotor [stator windings].

Try http://en.wikipedia.org/wiki/Alternator

for more explanation.

I believe it may be the "Frame 5" gas turbine which is 6500 rev/min, with a reduction gearbox to the AC generator.

Hello

Thanks for the explanation.Secondly i'm not very sure about the rotor speed as the speed is transmitted through a load gear box that is connected to the gas turbine.Can you pls explain the topic via simple line diagram as i am a beginner to this feild and am from the mechanical fraternity.

all that i want to clearly know is what is in the stator,in the rotor then what exactly happens when the rotor moves and which is the magnetic field and what does the exciters do and from where does the electricity generate and then details of the bus bar and if possible the governor connections.Thanks once again and pls do post

A good place to start - download this ABB demo

http://www05.abb.com/global/scot/scot232.nsf/veritydisplay/538923a1c1fa67e6c12572aa00349b96/$file/demo.zip

Some good illustrations (is your generator "Brush"??) :-

http://www.brush.eu/12194.file.dld

Do you not have generator technical manuals? - should have single line & other drawings.

The rating plates on the generator/turbine/gearbox should give speeds....

I may have to draw a diagram in the end.....

Begin here:

http://en.wikipedia.org/wiki/Alternator

Hello

I need a simple line diagram,b'cos the system in wiki is more related to auto powre generation,and my concern is in oil and gas sector where we generate power via gas turbines.

I'd like to give you 100 GA's for proper accreditation.

But am allowed only 1

'Respect'

nelsonaugustinec:

What do you mean by " simple line diagram"?. We will have single line diagram and control diagram only.

Thanks,your answer was very concised and to the mark.All i wanted to know was the basic concept of the working principle and you have provided me with a very simple answer.Thanks once again.