Head scratcher here... I'll start by saying I didn't do it! Really!
A neighbor has a Pump>Belts>Generator hydro setup that has recently had substantial re-build work done by two different people. Neither one is an electrician. It's not working. Yet.
About four months ago, Local Guy One replaced the pump. He's a little short on common sense... When he unbolted the pump, he forgot to make sure the 300' long, 15" diameter penstock was empty... It was only partially full, so he's not dead. But the whole powerhouse got soaked. It took him about two months to get the pump changed out. During which time, the bearings on the generator rusted up.
When he fired the thing up, it put out power, but made an awful racket, as you would expect from a rusted up 60kW motor... They let it run overnight then shut it down. Enter Local Guy Two.
He replaced the generator bearings. Which, of course, meant he had to disconnect <all> wiring, pull out the armature, etc. He changed out the diodes on the field bridge because they were brittle and crumbly. He marked everything, drew diagrams and, supposedly, put it all back like he found it.
When they fired it up, it mechanically ran better than it ever has, according to my neighbor, who has owned the place for the last 10 years. Only problem is, it ain't puttin' out no power!
Local Guy Two has been asking other locals (not including yours truly) and going back and forth trying to diagnose the thing for the last month, without success. I went over there with him last week to take a look.
I have dealt with a lot of industrial things in my life, but I've never seen this exact setup. For one, the generator says it's a "Single or Three Phase". Second, it's self-excited. I've always worked on line-commutated stuff.
The thing is basically a 60kW 3-phase alternator.
The nameplate says the field voltage is 50 volts at 1800 RPM. It's obviously not that excited because it's only putting out 4.2 volts. Is there such a thing as Viagra for generators?
We flashed the field with 12, then 24 volts. Running and not running. No go. I am sure there's a field present because i get floating resistance readings across the coils. It counts up with tester leads connected one way. Down with them reversed. Readings are 100's of K and low M ohms.
Is this too high? If i add up the approximate values, A+B=C.
I removed and tested the voltage regulator according to the factory procedure. It checks out OK. <The procedure seems overly-simplistic, so I still question whether it's OK or not> Put it back in. Same story.
I have a question about the bridge... There are 8 diodes. Three windings. Each winding is connected between two diodes. One of these diodes is terminated on a Positive buss, the other on a Negative buss. That leaves two diodes connected between the busses. What are the "extra" diodes for? Is it possible that they are only for balance and should not be connected together? Local Guy Two said he put the diodes in correctly (buss>anode>winding>cathode>buss).
The neighbor talked with one of the other neighbors who was trying to help. That neighbor had talked with the factory, and they said to run the motor at 1000 RPM for three days to make sure it's dried out completely. It is currently running at 1000 RPM....
Would appreciate any thoughts or help any of you all might have...
Thanks in advance!
Generator Nameplate: http://sdrv.ms/ND9YPW
Bridge Pic: http://sdrv.ms/NfAQqh
Here are the specs on the generator:
Kamag  Brushless AC Generator
Single or Three Phase
50 or 60 Hertz
Serial # 86284
Catalog Code 4P1-1150
Model # 60EX9E
Type # 21550
Exciter Field Volts 50
Exciter Field Amps 1.25
Temp Rise 80R *C
Design Ambient 40*C
Insulation Class F
Solid State Voltage Regulator
Sensing 240,480 VAC
Power 190-277 VAC, 650 VA
Output 63 VDC, 5A
Oper Freq 50/60 Hz