High voltage power transmission

[Warrior]

Hello Group,

I been looking at high voltage systems that use a transformer far away from the tower and then lower the voltage to charging levels near the battery. They usually transmit at 120 to 240 volts ac or more.

Searching for information I downloaded the Whisper 500 users manual and it seems that the turbine is hard-wired dierctly to the transformer and then to the battery charge controller. Is it possible that they've wired it directly?

How much low wind performance will it loose? Will it be much harder to start?

To quote the manual "In winds below 7-9mph (3-4 m/s) the propeller will not start from a dead stop. In winds above 7-9 mph (3-4 m/s), the propeller will begin to turn slowly".

Doesn't seem like an elegant solution, as other turbines such as AWP use solid state relays to connect/disconnect the turbine to the transformer, but it does seem simple and more reliable with less things to go wrong. Plus you get variable voltage.

Below are a few schematics from the user's manual.

Your opinions are welcome.

Warrior

[Nando]

Warrior:

The use of transformers to raise the voltage for long distance transport is a logical way.

What is important in this set up is the initial generator frequency at low wind velocities.

A good number of these systems, connect the transformers once certain voltage level is generated, which at the same time represents certain minimum frequency generated.

The shown system has a 3 phase transformer ( or 3 transformers) connected with arrangements for 12, 24, or 48 volts. ( 12 and 36 in Delta and 24,48 in STAR connection)

This conversion to start to charge will require a minimum certain incoming voltage that most of the time is designed for the cut-in range and the transformer geared to support the high peak power.

The transformer in some cases require greater metal core volume for operating at low frequency if the generated power may be a bit high, (at low frequency), it is a balance between generated power and frequency.

The system, you have shown, seems to cut-in at higher wind, though the wind mill may be rotating without load until enough high voltage is generated to convert to the battery via the transformers.

Some systems do connect the transformers directly and some use semiconductors to insert the transformer to the wind mill.

Some other systems convert without transformers via a 3 phase rectified DC/DC converter for higher charging operating ranges.

To optimize this system, it would be good to have a higher voltage in the secondary with a charge controller with MPPT capabilities to harvest the peak power of the wind mill.

Nando

[finnsawyer]

At the risk of getting my head chopped off again, I'd like to suggest you consider going to single phase, as that would require only two wires from the tower and one transformer.  Furthermore you might check my diary, the link to which is below.  This design should provide more than four times the output voltage of an equivalent three phase with the same number of the same magnets and the identical coils.  It should also provide three times the frequency.  That is, when the three phase is putting out 12 hz at cut-in this alternator would be putting out 36 hz, which would better match the transformer characteristics.

     http://www.fieldlines.com/story/2006/4/21/16237/9933

[Warrior]

Dear  Nando,

Thanks for replying to my post. I understand that the wind mill will cut in once the transformer's secondary winding reaches the correct battery voltage.

On the other hand, will the windmill have any load/drag prior to cut-in being that it's wired direct to the transformer's primary coil? That's my main concern regarding this system.

To sum up from reading the board, so far it has been mentioned that in order to keep the transformer core small, forget working with low frequencies.

This can easily be solved by having a large pole count in the generator design so that it reaches 45-50 Hz at a low enough cut-in rpm.

Second, the primary winding should be designed to handle roughly twice the cut-in voltage at peak power.

I really like your idea of going with MPPT electronics, but I have little experience with electronics.

Designing a suitable transformer is something I can do.

Even if someone posted a working MPPT circuit, I'm almost positive that in my county, the parts will be very hard to source and even if they are available it would be much cheaper to build the coarser transformer system.

I'll have to settle with 50% or lower efficiency for now.

But on the other hand I have a very simple and versatile system that will enable me to use thin wire, have very low transmission loss, and selectable battery voltage.

Thanks,

Warrior

[Flux]

Whether or not the transformer affects start up depends largely on the flux density in the transformer core. If the flux density is fairly low then most likely the transformer can be left in circuit during start up without adding significant drag.

If the flux density is higher and nearing the saturation point for the core then the drag may be heavy and you will need to remove the transformer during start up.

Low frequency requires large cores and lots of turns and transformer cost, size and efficiency suffers. There is then a tendency to cut cost and size by working at the highest practical flux levels.As the voltage is clamped by the battery, the core flux falls with rise in speed so it makes some sense to push the transformer very hard at cut in. Starting and low wind performance may be traded off against transformer cost and higher efficiency higher in the power range.

If you adopt the mppt approach then volts will rise with speed and the transformer flux level should remain constant. In such a case it would be less attractive to over flux the core in low winds and during start up.

For a transformer scheme to be reasonably cost effective and to keep transformer efficiency reasonable then I would look for alternators with higher frequency than the normal 12 pole axials. The low frequency of 2 and 4 pole motor conversions makes them very unattractive for any transformer scheme.

The cost of the transformer will be a considerable part of the total cost if you want a decent efficiency.

Flux

[wdyasq]

GeoM,

Could I please see the test data on that mill?

Thanks in advance,

Ron

[BigBreaker]

This is why you might want to use FETs to flip the signal going into the transformer back and forth at a known higher frequency.  You can then use a much smaller transformer and the transformer gain will be more stable.

Switch mode power supplies use this trick to get away with tiny cores.