Troubleshooting “Little Jake”: Page 5 of 5

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Troubleshooting “Little Jake”
Stepping through the troubleshooting and repair process on a vintage Jacobs wind turbine.
Little Jake needed to come down for repair.
Based on troubleshooting tests, Little Jake needed to come down for repair.
Little Jake’s tail was manually furled out of the wind
Little Jake’s tail was manually furled out of the wind so tower wiring could be checked.
The controller box
The controller box was tested and diagnosed.
Diversion controller, dump loads, and DC panel.
Diversion controller, dump loads, and DC panel.
RE systems’ balance of system (BOS) components
The RE systems’ balance of system (BOS) components, including the charge controller, battery bank, inverters, and DC and AC load power centers.
A megaohmeter (megger)
A megaohmeter (megger) was used to test the THWN conductor insulation.
Yaw slip-ring brushes.
Yaw slip-ring brushes.
Yaw slip rings.
Yaw slip rings.
A high-potential (hipot) tester
Testing for shorts from the conductors to the metal tower was accomplished with a high-potential (hipot) tester.
Testing in the shop
Testing in the shop revealed an internal short—a short from wire to wire—in the armature windings.
Testing in the shop
Testing in the shop revealed an internal short—a short from wire to wire—in the armature windings.
The front end of the generator
The front end of the generator. The blades would be attached to the long shaft.
The rewound armature.
The rewound armature.
Troubleshooting “Little Jake”
Little Jake needed to come down for repair.
Little Jake’s tail was manually furled out of the wind
The controller box
Diversion controller, dump loads, and DC panel.
RE systems’ balance of system (BOS) components
A megaohmeter (megger)
Yaw slip-ring brushes.
Yaw slip rings.
A high-potential (hipot) tester
Testing in the shop
Testing in the shop
The front end of the generator
The rewound armature.

So we packed it back up and sent it to a motor rewind shop, where the insulation was burned off in a kiln at high temperature. Then, the technician diagrammed the geometry of the wire connections of the various coils in the wire slots in the armature. This Jake has 47 wire slots in the armature and 94 bars on the commutator that the wire coils are soldered to. The coils were formed with flexible insulated copper “motor” wire and replaced in the slots in the armature, with the coil ends soldered to the commutator in their original geometry. Once rewound, the armature was baked again, but at a lower temperature, which drives off any moisture. The warm armature was dipped in motor-insulating “varnish,” then re-baked to set the varnish. Excess varnish was cleaned off the armature and commutator. The varnish also had to be cleaned out of the slots between the 94 bars in the commutator so that the varnish doesn’t gum up the commutator brushes. Once this was done, the armature was reassembled in the generator and the whole thing was bench-tested again to confirm that it worked as it should. Rewinding is fairly complicated­—to say nothing of being tedious—and it’s best left to patient technicians who know what they’re doing. The average rewind shop would likely charge between $1,000 and $2,000­—the labor is intensive and insulated copper wire is expensive.

By January, we had a freshly rewound, slightly modified armature. With one extra winding turn and 11 AWG wire instead of 10 AWG, the machine would from then on produce higher voltage at a lower rpm, but have a slightly lower current-carrying capacity. We tested the armature on the bench in Mick’s shop, then reassembled the machine and brought it back to the MREA. 

Little Jake Lives On!

Thanks to an unusually warm spring, we were able to get a crane to the MREA in early March 2012 and reinstall the machine. Mike had repainted the turbine a sparkly royal blue normally reserved for muscle cars. Not only did it look better than ever—but it worked, too!

Little Jake still requires maintenance from time to time, as all wind turbines do (being exposed to the vagaries of wind and weather is tough on mechanical equipment), but we keep it in perspective. You wouldn’t drive your car for months and months without so much as an oil change or a brake check, would you? (If you answered yes, then wind turbines aren’t for you!)

There’s really nothing we could have done to prevent an armature failure. Motion in a generator is unavoidable (if the turbine is actually turning). Heat can be dissipated in various ways, but this is taken care of in the generator design. The best thing an owner can do is to make sure that, in the case of a generator, the commutator brushes are in good shape and seated properly so they don’t arc, since this creates heat. But the environment wreaks havoc on insulated wire, just as it does for electrical wiring in an unheated garage or a chicken coop­—so there’s not much you can do, unless you leave your wind turbine parked in your living room.

The other thing that can “prevent it from happening again” is to find a quality rewind shop that uses quality insulated wire and varnish. Cheaping out on these with cheap materials invariably means that you’re going to be at it again until you figure out that this is not the place to cut corners.

Today, Little Jake is nestled behind the Renew the Earth Institute at the MREA on its 100-foot lattice tower, delivering electricity to the premises. We know that it will still require some tender loving care from time to time, but if this armature lasts as long as the original, we won’t have to worry about another project of this caliber until about 2080.

Access

Jenny Heinzen is the curriculum and training coordinator for the MREA. She is a licensed master electrician and electrical inspector in Wisconsin. She works with organizations like NABCEP and RENEW Wisconsin to promote professional installations and supportive renewable energy policies, but her favorite days are those spent on a tower.

Midwest Renewable Energy Association • midwestrenew.org

Comments (1)

Lindsey Roke's picture

I was interested in the trouble-shooting approach.
It appears to have followed what we might call “the aardvark method”.
(“I am thinking of a word in the dictionary, what is it?”
“Is it aardvark?”
“No”
“Is it aardwolf?”
“No”
Etc.)
This method will eventually find a fault but it but it is not the fastest – and without due care has the potential to introduce more problems if (for example) connections are not done up again correctly.
Here in New Zealand I work for an appliance manufacturer (Fisher & Paykel Appliances Ltd.). In managing production engineering I have always been intrigued by various approaches to trouble shooting. We learned a great deal from the late Dorian Shainin when we had him here running some training sessions for us. (Look him up on the web is you are not familiar with him.) The technique he would propose for the dictionary would find any word with about 17 questions requiring just yes/no answers. (Find the middle page and ask if the word is before that page. Then go to the quarter or three-quarter point as appropriate. 11 questions will get you to the right page in a dictionary with up to 2048 pages. The next question gets you to the right column. Assuming there are no more than 32 words in a column, 5 more questions will get you to the right word.)
I recall one factory break-down where the photocell sensor was supposed to detect a cabinet on the assembly line, send a signal to a microprocessor controller, which in turn was supposed to drive a solid state relay which switched a hydraulic valve that operated a piston that did something useful. The problem was that when the cabinet went in front of the photocell the useful action didn’t happen. While I could have started by checking that the photocell was working, it was much quicker to repeatedly “cut the problem in half”. Because we had indicator lights across the electrical connections on hydraulic solenoids, (put there when the equipment was installed for just such trouble-shooting) the first check was to see if there was power getting to the solenoid when the photocell was triggered, etc. etc. (Without the indicator lights, the same thing could have been done with a meter – but when an assembly line is stopped, time is of the essence.).
You can bend the rules a bit if there is a very easy point to check that is not mid-way through the problem – or if there are other clues as to where to start looking.
I have learned that, if a piece of equipment has been operating OK and it stops, unless somebody has already had a go at trouble-shooting it by swapping components in and out before you arrive, it will very very rarely have more than one fault.
My objective, when called to an intractable malfunction, is to determine which component is faulty, get the tradesmen to replace it and walk away with confidence that the machine would work when they have done so.
While the mid-point of the Jacobs system in the article might be the input to the slip-rings, to save climbing the tower, checking first whether or not there was a voltage at the bottom would have isolated the problem to either the Balance of system and wiring to it from the tower or – to the generator, slip-rings and tower wiring. The next check at the generator terminals would have put the fault in the generator or in the slip rings and tower wiring etc.
(I’m not decrying checking such things as the brush and slip-ring condition while up the tower – but as maintenance tasks not as trouble-shooting in this case.)

Shainin, in my opinion was better (at least in this area) than either Joe Juran or Edward Deming – but not so well known, probably because he was better at solving problems than writing books.
I trust this might be useful.

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