Brushless Generator Exciter Stater

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The new A.V.R can drive the exciter but there is no sufficient supply voltage(enough voltage) from generator to feed the exciter via the A.V.R .that is clear when you load the generator .i advice you don't rewinding the exciter stater . read the instructions (data sheet) of the new a.v.r carefully and try to connect it in right way

hi mr caeser, thanks for your reply

on the name plate of the avr it says that the maximum output dc voltage is 60vdc. i did installed about 100 piece on different generators. its not complecated to connect, it has just 4 terminals, 2 of them are the 220v input and the other 2 are for the dcv output (+ and -). i am pretty sure that its not connection matter.

as i worked with this avr before, i found that the maximum vdc out is not 60vdc as it says on the name plate, but its 82vdc.

now when i tried it on this generator, the output dcv from the avr is about 76vdc to make the generator output 380vac without load, now how many volts the exciter stater need, to make the generator output 380vac on full load. i dont think it needs 82vdc to do it. i guess it needs around 150 to 200vdc to do the job.

which sure can not be supplied by the new avr.

it needs avr with around 200vdc output which i could not find here.

so i thought the best solution is to change the resistance of this exciter stater as this solution can be done here.

why you adviced me not to rewind it?

can it be done or not and why?

i appreciate your help

You are right when you said that you need 150 VDC minimum on 60 Ω because you need > 3A for the maximum load.

Rewinding the exciter requires more experience and workout to know if the Amp-Turns you will get will be sufficient to create the required excitation current, eventually, for the rotor field....

hi mr LAA Lucke,

i did rewinded the exciter stater with thicker wire size and i tested on load. the new winding resistance is 13 ohms, the no load exciter stater volts is 30vdc and 85vdc on full load. the winding temperature is ok for one hour running on full load. i think its ok now and all was because if your support which helped me to go forward. and thanks for all of you guys.

i appreciate your help

Yes don't try to rewind the exciter stater because you will make changes in the design of the brush less system (rotor three phase exciter +main rotor exciter=armature,and particularly in the exciter stater) .and you can not make a design best than the manufacture company that did . if you are sure that the defect is due to lake in the A.V.R's work try to repair it that is good solution and short.and may be Little cost

You are right about rewinding the stator of the exciter. It is better to either repair the original AVR or replace it with the same or equivalent unit that can supply the required Amps etc.

But, Theoretically, there is no reason to avoid stating that it is possible IF YOU HAVE the necessary knowledge and means to do it. It is up to the OP to decide, on his turf, if it is worth going this or that way.

some times more explanations confuses the one so i avoid that .when he shall going to rewind the exciter stater coil . he shall decrease the number of turns of the exciter for this case .what will hapn to the exciter? the exciter will draw high current from the a.v.r under low voltage to produce a mount of power magnetic as you know the heat that develops in the exciter coil will increase due to increase in the current and may damage the exciter coil .the question here why you produce this amount of magnetic power by increase the current, you can make that by increase the voltage that feed the exciter coil and generate the same amount of the power magnetic without increases in the heat of the exciter.as you know the POWER LOW is is P=V*I .

Ok

But in this case, the heat is RxI^2 and the Magnetic power is Axt (Ampere x Turns).

In which case, higher voltage into the same R gives more Amps so that he gets the Axt required. Therefore, the Amps must increase to ~ 3 + for this exciter/Alternator,

If he reduces the turns, he must use a thicker gauge wire to get the lower Ohms.

etc... no so simple, but possible to work out or at least to check if possible to be done on this exciter Stator. It might be impossible or needs compromise on the output etc.

That is why I said it was not easy. It is up to the OP to understand where he is going and how difficult it may be. --> educative ??

Yes .

what i meant it that he produce amount of magnetic power from electric power and it is equal VXI the R of the exciter coil is not constant ( pure resistance) it is impedance and a pure resistance works together .the heat is liner with I^2 if you want to increase the current you will decrease the voltage to get the same electric power that produces that amount of power magnetic . the changes in the load of the out put's generator will change the impedance and due to that a current passes through the exciter coil without any changes to a setting voltage that apply by the A.V.R . V of exciter stater is constant

Caeser, I am finding it difficult to understand correctly your writing.

However, I will have to say that the Stator of the exciter is fed DC current and as such, the impedence is practically resistive only. We will have what is called a counter voltage produced by reaction from the rotor. The OP says that he measured the Exciter Stator resistance and it was 60Ω, which makes sense with his new AVR behavior.

First, he needs the correct AVR to be able to drive the exciter properly. The one he is using seems too small to drive it since it can only develop a lower voltage and current.

Second, if he wants to re-wind the Stator so that he can drive more Amps into it, he should know that what he must aim at is the Amp Turns and not just the Amps. Also, as you rightly pointed out, he needs to consider the overall heat to dissipate.

There is more to it than just re-wind it. But if he thinks that he can handle all the problems we pointed out to him, then it will be up to him. The cost and time delay to replace the AVR against the cost and also the delay to rewind + the risk of not doing it properly --> replacing the exciter again ... have to be considered.

M.r Laa lucke i wort summaries about all things . and here is a summary of what will hapn if he re-wind the exciter with thick gauge wire as you said before .

1# he needs an A.V.R can drive high current into exciter. 2# when the generator works under the full load the re-winded exciter stater draws from the A.V.R a maximum current higher than what the original exciter draws at full load .what the problem if the current becomes higher in the re-winded exciter for full load case generator ? i will answer . the temperature of the re-winded exciter increases with MAX current ^2 this is the math. relation between the heat and the electric current , for long time of the generator's working the heat of the re-winded exciter increases(as you know the stator exciter has no cooling system ) and the lines of the magnetic field that is produced by re-winded exciter becomes un regular and this effects at the quality of the electric (generate a sin wave not pure) the all issue you have to match among all these elements (the temperature of the exciter coil and its current at full load and the quality of the electric (the purity- pure sin wave).

#1, OK, we know that.

#2: There is no reason to argue this point. It is more complicated than just as you stated. You can be right if the details of the re-winding were not properly worked out.

BUT, I stated that the most important issue is that he gets the Amp.Turns correct while the copper wire gets also thicker. The AVR regulates the current in the field winding so that the output voltage is maintained as the load increases.

Now, the biggest problem that comes after that will really be the AVR's capacity to provide the Amps required at full load!

The excessive heating of the exciter stator might not be so out of range if the re-matching is possible or was made correctly. THIS IS THE Question mark.

On the whole, this argument is not necessary, here, between you and me. I understand very well the problem. The point is to make the OP aware of the challenge he will face if he wants to go ahead and rewind the exciter's stator.

Rewinding the exciter is not an option. If you have a brushless excitation system then you have to determine if any of the fuses, diodes, or the rotating windings are open or shorted. 40 year old fuses and diodes are suspect, as are any crimped or mechanically joined connections.

Look for corroded or poor connections, everything may need to be recrimped and retightened. If everything is not perfect from the input to the AVR to the input of the main field winding then there may be a high resistance contact point that is causing a voltage drop and subsequent current limiting under other than no-load conditions. Only a thorough inspection and tightening will eliminate this problem.

Check the diodes