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Turbine failure
By Seedler, Section Wind Posted on Fri Aug 1st, 2008 at 02:11:24 PM MST
Need help with electrics

Hi folks,
My grid tie, chinese made turbine is not working. I'll give you's the background before I ask the question.
I bought a 3 phase 3kw turbine a year and a half ago. It is in the style of an electric motor. It is connected to a wb3000 inverter.
The first problem was the voltage. The turbine was a 240v output but the inverter required at least 300v in order to connect to the grid. The turbine did get to this voltage but it took alot of wind. I finally got this problem solved by adding a transformer that the manufacturer sent the specs for. After it was installed the turbine got to the voltage more easily and connected to the grid easier. The problem with the transformer was when the turbine rpm got below a certain point it would not start-up. I lived with this by letting it run open circuit until it got the rpm's up.
Now for the latest problems. A few weeks ago it seemed not to be running so freely. Then a week ago it stopped. I took it down and found that one of the bearings had worn out, and the magnet rotor was stuck to the coil laminates. The rotor paint was slightly scraped but nothing serious. Nothing tuched the coils and they looked fine. I replaced the bearing and put it back together. The shaft was hard to turn by hand, but it was hard to turn when I bought it, so I thought nothing of this. Anyway I put it back on the tower and waited for the wind but when it came the turbine only moved very slowly and wouldn't start. it was not like the brake style short because this stopped it completely, it was as if it was through the transformer. I disconnected everything and checked resistances. (I dont know much about resistance but thought I check anyway) I couldn't get a reading of the resistance between the phases because it kept jumping around alot, but I accidently found out that there was a connection between the phases and the mast and earth. This doesn't seem rite to me. Am I rite in thinking that this should have read as an open circuit? Would a short to earth cause the braking effect? And does anyone have sure fired ways of testing the coils in a 3 phase turbine?
Sorry for wrambling on. Hope you's can help.
Dee.

Turbine failure | 5 comments (5 topical, 0 editorial)

Re: Turbine failure (3.00 / 0) (#1)
by Flux on Fri Aug 1st, 2008 at 08:26:41 AM MST
(User Info)

I think I have bad news for you.

I think what has happened is that the bearing failure has let the rotor rub the stator hard enough for a few stator laminations to have been dragged round and one of these has cut the winding. You should have no circuit to ground and if it was working before the bearing failure.I suggest you have a look at the "teeth" of the stator to see if any have been dragged round.

Whatever the cause, the failure you have has all the symptoms of a faulty stator, it is a rewind and you can now change the turns and wire size to replace the nuisance of a transformer and get it running as originally intended. Don't use Chinese bearings in the rebuild either.

Flux

Re: Turbine failure (3.00 / 0) (#2)
by oztules (oztules__at__bigpond.com) on Fri Aug 1st, 2008 at 10:10:46 PM MST
(User Info) http://www.anotherpower.com/gallery/Oztules-toys

" I couldn't get a reading of the resistance between the phases because it kept jumping around alot,"

This is the same problem I experienced when testing the AWP windings. It seems that the digital multimeters cannot have magnets near the copper coils you are trying to test.

They must pulse the current in the coils or some such thing when measuring the resistance, as you will only get a reading if you seperate the stator from the magnet housing. It is not possible I have found to measure resistance if the coil has a magnet in the near vacinity.

( I'm guessing it is the sampling pulses that mess it up)

Is this a radial type or axial type of alt?
If radial, then as Flux said, look for laminates that no longer line up with their brothers and sisters. They chop the coils quite well I have found.

..........oztules
Flinders Island Australia

Re: Turbine failure (3.00 / 0) (#3)
by Flux on Sat Aug 2nd, 2008 at 02:46:54 AM MST
(User Info)

I have not had trouble measuring resistance on permanent magnet alternators if the rotor is absolutely stationary. If the rotor moves even slightly then the induced voltage will be greater than anything the meter is measuring in terms of volt drop.

With a high voltage alternator the required movement would be tiny and perhaps there cold be a problem. I assumed the trouble was the damaged and most likely cut winding causing the variation.

Remove the magnet rotor. Multimeters are only a rough guide and are not satisfactory for measuring this sort of resistance in most cases but should show obvious differences.

You are looking for shorted turns in this case and even a decent resistance test will not discriminate a turn or two shorted. Energising from an ac supply and checking line currents would show it better if you have suitable supplies and facilities but as you have an earth fault and drag you can be sure the winding is damaged.

Flux

[ Parent ]

Re: Turbine failure (3.00 / 0) (#4)
by Seedler on Sat Aug 2nd, 2008 at 02:57:26 AM MST
(User Info)

Hi,

Its a radial (looks like an electric motor). I think you's might be right about the laminates. I never knew to check them but it sounds like a good explination.

If I were to get it re-wound to a higher voltage using smaller wire would that effect the output, is there more chance of overheating with smaller wire?

How do I work out what size of wire and how many coils and turns I need. Or would a re-winding company be able to work this out for me?

I have attached the plans for the transformers that the manufacturer sent me. they say the output voltage of the turbine is 240v and the output voltage of the transformer is 350v. So am I right in thinking I should be re-winding to 350v.

Thanks again for all the help. Hope the pics aint to big.

Dee.

Re: Turbine failure (3.00 / 0) (#5)
by Ungrounded Lightning Rod on Mon Aug 4th, 2008 at 03:13:04 PM MST
(User Info)

If you get it rewound with wire with the cross section reduced in proportion to the increase in turns ratio you'll get the same percentage loss at any given POWER output. It will do the same thing as your external transformers, but without their losses.

A motor or generator is just a transformer with one of the coils replaced by a magnetized rotor. You can adjust current and voltage, keeping the power (product of current and voltage) constant by adjusting the turns ratio. And if you keep the same total cross-section of copper in a coil you have the same resistive losses at a given POWER and RPM combination (except for eddy current losses which go down with thinner wire).

[ Parent ]

Turbine failure | 5 comments (5 topical, 0 editorial)

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