Leroy Somer R449 AVR

My guess is that the instantaneous current passing through it is more than it is designed to sustain.

Your replies so far are of the obvious nature.

The specific info I need is related to what is blowing the fuse on the AVR. Following testing and meggering of the main field windings, the auxiliary windings (AREP excitation system) and the excitation winding itself, it appears that all reads correctly and there is no obvious evidence of damage. Rotating diodes and surge supressor also reads correctly and there is also no sign of damage.

I am hoping that someone with deeper understanding of these types of alternators can shed some light and/or steer me in the right direction.

Which comes first, is it the AVR or Alternator?

Obviously, the alternator, then the AVR and then the load -whatever hooked in line with it.

Isolate the problem one by one, look for the root cause why the fuse blows up.

First, which comes first, the demand or the supply?

Of course the demand, agree? Now, what do you think is causing it? Is it the alternator or the load itself?

Suppose let us say, the alternator as you cited is defective, say one pole winding burnt, what would be the consequence? If its three phase, you suddenly have an out of phase supply. Which comes first "out of phase trigger" or "fuse blown out"?

Now, suppose I have a grounded wire from AVR to load, what will happen to the AVR?

Obviously, fuses blow up, depending on which phase line is affected.

Now, where were we? You answer.

The AVR sensor setting for voltage or hz could be set incorrectly....could be wrong type of fuse...I would review all the settings on the AVR and check if fuse is slo blo..

https://library.e.abb.com/public/26122c0018fa02eb482577ce0023b51b/5855292-AVR%20USERS%20MANUAL%20EA63-5%20C.pdf

If you have read the manual then you would know that the normal current drawn by the AVR is only 7 amps, so the first things I would do is ensure that you have used the factory specified fuses, then isolate the regulator from all the other inputs/outputs and measure the current draw.

If it exceeds 7 amps then you have not set the AVR up properly or the board is faulty; if it doesn't then you should reconnect the previously removed leads one at a time until the current starts rising and/or the fuse(s) blow, you will then know where to look for the cause of the excessive current.

It's really a matter of understanding what you are working on combined with good troubleshooting skills.

Looking at the R449 Installation and Maintenance Manual, I'd say the most likely cause is a shorted diode in the voltage sensing circuit.

I'd also say that your best resource to answer this question is the support group at Leroy Somer. Contact information is listed on the last page of the manual.

Thank you for all the info! Much appreciated.

It appears that, after completely isolating the main field lugs from the alternator busbars, that two of the main stator field windings reads 0 Ohm to earth when cranking between the winding and earth on the MegOhm scale. (this should read infinity - ∞)

This means that the main stator field coils are down to earth, and obviously responsible for the blowing up of the AVR.

So it looks like a very expensive 3Phase/1650KVA Leroy Somer alternator will be going into the dumpster since there are no armature winders where we are, in the swamps of the Niger Delta in Africa.