Three Phase Generator Excitation Polarity

In general the polarity for the exciter or the generator rotor should not matter. The problem is at the exciter because there you have the exciter controller - the automatic voltage regulator.I am sure your AVR does not rely on an old potentiometer but it has a static switching current controller. For the exciter current controller the polarity is important, after all the controller has some transistors and other electronics that impose a specific polarity.

hi, thanks for your reply

yes, you are right. it is not old potentiometer, it is static switching devices AVR. and i understand that there is polarity on the output to the exciter stater, they are marked as F+ and F-

so F+ is the positive and F- is the negative, but i am talking about the exciter stater itself, it has 2 wires, one marked + and the other marked as -. i understand that excietr wire which marked + should be connected to F+ of the AVR and exciter wire which marked - should be connected to F- of the AVR.

my question is why when swap the exciter wires, + will be connected to F- and - will be connected to F+ the generator will not generate power?

the second question is, lets say i will not swap these exciter wires, but i will swap the wires of the main generator rotor, which are connected to the bridge rectifier heat sinks, i noticed that this action will not effect the generation and the generator still working fine?

hope you got what i mean!

thanks again for your reply

You could try to start the generator without powering the exciter from other source but the generator output. If you can start the generator only using its remanent magnetized core than the guys are right, the remanent magnetization is high enough as not to be overcomed by the reverse field. I know this stuff works for DC generators because I tested it. For AC generator I have not tried but is about the same stuff.

everything in the whole concept is based on the direction of rotation,in relationship

to the stator and rotor connection. the exciter is to insure polarity and not to use

any power from the main winding for excitation. as you switch the polarity on the exciter you are directing current to a rectification component,which only rectifies

to a correct polarity. as you attempt to change direction of the main generator

you are not doing anything. your exciter can be disconnected and the main generator

will work from residual magnetism which you are proving by the polarity reversal of

the exciter. in the case of a brand new generator or a new rewind you have to

establish polarity which will not be there. (enter the exciter) if on a new generator

or a rewind there isn't any current being generated, most always look to the exciter and all the associated excitation circuitry and components first. to further mention

(polarity) newly installed auto generators had to be polarized from the battery

to insure generation.

I don't think that changing the polarity of the exciter field (Stator) will have any effect as to the power/Voltage generated at the Main Alternator Stator 3 phase AC.

The exciter is not polarised by itself or by desighn except that it needs a DC current to the field. The AVR delivers the DC and does not care which way it flows in the field windings.

The experiment described by the OP is not accurately described as there could be other things he might have done or failed to notice.

The simplest explanation (not very conclusive) will be that the remanent magnetism in the exciter was not being reinforced to escalate by the AVR, but was cancelled instead, making the exciter too weak to generate any voltage. The rectified current going to the main winding will have the same polarity as before, but the AVR will be using it to cancel the remanent magnetism in the exciter...

The Main Alternator remanent magnetism will remain. Thus when reversing back the exciter field, you might be able to re-generate the full field.