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Shock Absorber
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4 Posts
Discussion Starter · #1 ·
Hey All,
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 ****** 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!
~Skip

Generator Nameplate: http://sdrv.ms/ND9YPW
Bridge Pic: http://sdrv.ms/NfAQqh

Here are the specs on the generator:
Generator

Kato Engineering
Kamag [14] 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

3-Phase
KW 60
KVA 73
HZ 60
RPM 1800
PF 0.8

WYE
Volts Amps
208-240 200-181
416-480 104-91

Delta
Volts Amps
120-139 359-313
240-277 181-157

Temp Rise 80R *C
Design Ambient 40*C
Insulation Class F
Duty Cont
Wire 12

Voltage Regulator

Basler Electric
Solid State Voltage Regulator
Model APR-63-5

Sensing 240,480 VAC
Power 190-277 VAC, 650 VA
Output 63 VDC, 5A
Oper Freq 50/60 Hz


Thanks everybody!
~Skip
 

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Donuts > Fried Eggs
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17,042 Posts
I'll re-read this when I get a minute because I have the feeling I'm missing important info.

One question: You say you're sure the field is present because you have a floating resistance measurement. I don't follow what you mean by that?

If your field was present, you would have voltage on your stator, it's really that simple. If you think you have open windings because you're not measuring anything on the leads, then you can measure the voltage across individual poles.

Are you sure you're flashing the field at the right polarity?

The two shunt diodes are your snubber circuit for the field if the unit trips under load, it prevents an inductive kick that would short out your rectifier.

-John
 

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Shock Absorber
Joined
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4 Posts
Discussion Starter · #3 ·
Hi John,

Thanks for the note on the snubber circuit. Now i know!

RE: Floating... I was talking about the motor windings. I checked resistance across the motor leads. There wasn't a steady, solid reading on any of them. The readings were more like reading a capacitor bleeding off, except they counted up when i reversed my test leads. I call this condition "floating".

Maybe I have an incorrect understanding of the field relationship here...??? My understanding is that the exciter field can become de-magnetized if it's left de-energized for a period of time (like it was). The purpose of flashing the field is to re-magnetize it, right/wrong? I interpreted the floating across the motor windings to indicate there must be a significant magnetic field present and thought that must be the exciter field.

Am I totally on the wrong track? Do i need to unsolder the exciter field leads from the bridge and test those windings and the bridge diodes, by any chance? If so, what type of values should i expect?

Part of my head-scratching comes from the fact that I don't understand the "Single or Three-Phase" thing, but that's not the source of the problem, so it doesn't matter. I think...

Thanks a bunch for your help!
~Skip
 

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Donuts > Fried Eggs
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17,042 Posts
When you say you're checking resistance of the motor, I'm not sure what part you're referring to.

In a brushless synchronous generator you're gonna have 4 windings:
1) Generator stator - The part where you're connecting the load you want to power.
2) Generator rotor - The DC field that produces voltage in your generator stator.
3) Exciter rotor - Sends voltage to your rectifier bridge to create that DC field.
4) Exciter stator - Induces the voltage in your exciter rotor.
So where on those are you checking voltage and resistance?

I'm gonna skip a lot of stuff and say I think the problem is one of three things:

1) The crowbar diodes the Local Guy Two played with are forward biased. They should not be. If they are, then they're acting like a short-circuit and that's why you can't develop a field, but I think this would also either cook the diodes or blow a fuse in short order.

2) Your AVR is cooked and is not able to provide the voltage going to your field. The easiest way to figure out if this is the case is to disconnect the AVR, idle the generator, and apply a low voltage from another source to your exciter stator. You will see voltage on your generator stator.

3) You are not flashing the field at A) long enough or B) the right polarity. You should let the current run for about 30 seconds to build a good field. If you do not match the positive to F+ and negative to F- that the AVR is using you may damage the AVR or just induce a field of opposite polarity to the one the AVR is designed for.

-John
 

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felonious smile.
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15,934 Posts
Get a hot young ho to rub her butt up on it, that will excite it....Unless it's gay of course.
 

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Registered
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451 Posts
When you say you're checking resistance of the motor, I'm not sure what part you're referring to.

In a brushless synchronous generator you're gonna have 4 windings:
1) Generator stator - The part where you're connecting the load you want to power.
2) Generator rotor - The DC field that produces voltage in your generator stator.
3) Exciter rotor - Sends voltage to your rectifier bridge to create that DC field.
4) Exciter stator - Induces the voltage in your exciter rotor.
So where on those are you checking voltage and resistance?

I'm gonna skip a lot of stuff and say I think the problem is one of three things:

1) The crowbar diodes the Local Guy Two played with are forward biased. They should not be. If they are, then they're acting like a short-circuit and that's why you can't develop a field, but I think this would also either cook the diodes or blow a fuse in short order.

2) Your AVR is cooked and is not able to provide the voltage going to your field. The easiest way to figure out if this is the case is to disconnect the AVR, idle the generator, and apply a low voltage from another source to your exciter stator. You will see voltage on your generator stator.

3) You are not flashing the field at A) long enough or B) the right polarity. You should let the current run for about 30 seconds to build a good field. If you do not match the positive to F+ and negative to F- that the AVR is using you may damage the AVR or just induce a field of opposite polarity to the one the AVR is designed for.

-John
John's hit all the points to check. I've troubleshot Kato brushless as well, the 2 areas that give us the most trouble are the stator exciter field, and the diodes on the bridge circuit.
from what you gave on the field specs, should see ~ 40 ohms resistance across the stator exciter. as far as your 4.2 volts initially, and the fact that you flashed the winding, w/no appreciable result, I'd also re-chk polarities. (we also have used 12 volt batt's to flash field windings when troubleshooting)
On the diodes, I'd undo the solder joints, chk them w/a diode checker to make sure they're good as well as being biased correctly/correct diodes.
I hate being third man in, never know exactly what everyone else did, and details get murky. Good luck!
 

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Shock Absorber
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4 Posts
Discussion Starter · #8 ·
Final Findings Update

Hey Gang,
Thanks for the advice and postings. Thought i'd post back with what it turned out to be...

Fried.

<Apparently> Local Guy Two shorted some motor leads when he was putting the thing back together. He neglected to mention this to anybody and hasn't been seen since. The autopsy indicated that he knew he did it because they had been taped up in the vicinity of the short. Just not good enough to prevent them shorting after all. The leads burned almost clear (trace amounts of copper left) but not before taking out the stator windings.

My best guess is that the floating resistance readings i was getting thru the windings weren't as much thru the windings as they were around the windings and whatever else happened to be in contact in there. All thru the trace amount of copper left in the motor leads, of course.

Re-wind estimate was almost double the cost of a new one. They've ordered a new, larger generator. Figuring out the pulley sizes and new shunt load scheme at this time. Genny delivery scheduled for a week or so from now. We're back in the woods so delivery schedules are pretty loose...

Thanks again for everybody's thoughts and advice!

~Skip
 
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