off grid system

[paul_66]

Hi,

 As part of a project/ work placement for my wind turbine course I need to design a system for a customer that will take on average 300 volts 3 phase wild AC and convert it to 48 volts DC to charge batteries, this 48 volt DC then must be converted to 240 AC for use on site. I am in Ireland.

From speaking to my lecturer he has told me that I first need to step down the 300 volts AC using a step down transformer (maybe 4-1) this will then be rectified to DC voltage. Which will charge the batteries. A system then like a Sunnyboy 6000 will take the power from the batteries and convert it to consumer voltage of 240AC.

I have been reading some on the internet, and one of my problems is that the voltage from the turbine could be anything from 50-500 volts. How do I make this constant so that it can be then stepped down by a transformer?

This is all fairly new to me, so I would really appreciate any information on what equipment I could use etc.

Thanks
 

[snake21]

hi,you dont need to transform any voltage.any wind turbine can produce voltage over the required voltage of the battery bank.the battery bank is here to lower the voltage.no need of step down transformer.

what you need to do is only to rectify the 3 phase ac current and connect the dc wire to the battery.then for off grid,you will have the dump controller and the dump loads and also an lvd for power output.there is nothing like your lecturer mentioned.
for example,if you spin your turbine at a certain rpm which will produce ,lets say,400vdc(rectified),then as soon as you connect it to a battery/or banks,the voltage will lower to the voltage of the battery.lets say from 400vdc turbine to 48v battery banks.
there is nothing to make the voltage constant except the battery

BUT,the battery voltage will keep on rising to reach 400v if you dont monitor the charging.dump loads are added to prevent battery damage.

you are new,you should read a lot friend

[wpowokal]

I suspect the poster has been give specs for a turbine that requires it's output stepping down (maybe a Windyboy http://www.sma-australia.com.au/en_AU/products/wind-energy-inverters.html), a turbine designed to perform at 300V will not do very well locked to 48V batteries, argument goes to design TSR and efficiency.

allan

[fabricator]

Why not just do it right and pick a turbine that is meant to charge batteries at 48 volts?

[wpowokal]

now that would not be very challenging for a student.

allan

[SparWeb]

Also not very challenging is hooking the turbine and batteries as they are up to an Aurora, but it would offer the opportunity to play with lots of software afterward (something students typically love to do).  It really depends on the lesson you are supposed to learn!

[paul_66]

Why not just do it right and pick a turbine that is meant to charge batteries at 48 volts?

I have to use the turbine, that is there

[paul_66]

I spoke to my lecturer about why I was to use a transformer to step down the voltage first, instead of using a ac/dc rectifier. He said that as the average voltage would be around 300 volts 3 phase ac.
the ac/dc rectifier can only step down the voltage so much and it will be better to use a transformer. So I have to use a transformer first, just need a solution as to how I can go about it

[ghurd]

"I have to use the turbine, that is there"
Is this something that will actually be built, assembled, and used?

There is a multitude of reasons to buy a factory made unit to do what needs done.

Transformer ratio must be suited to the wind speed.
If the system tries to start charging a battery when the wind is 4MPH, the system will not work much at all.

The 300V is at a wild frequency.  Many vary by over 400%.
Transformers have a design window of operating frequency, usually 50 or 60 or 400 HZ.
The chances of the alternator output HZ and transformer design HZ matching is very slim.

The output will be much higher with some form of fancy MPPT.
They are not exactly a DIY project for very many people.

If this is a paper and theory exercise, then a transformer to a rectifier is all you "need".
G-

[bob g]

it might be useful to know how many hz the wind gen runs at cutin?  or say at 6mph windspeed
if it is many poles maybe it can make 60hz at about a 6mph wind, if so transformers might well work ok?

the operating window for a 60hz transformer is up to 400hz and they will continue to function pretty well
way over that without much of a hit in efficiency.

i have spent some time working with transformers designed to run at 60hz on my 3phase test bed up to 600hz
and they work just fine

the problem i see with their use for this project is they really aren't well suited for the wild swing in voltage from cutin
to furling, you can match things for a specific speed/voltage but thing go out of optimum very quickly

tap changing as speed and voltage increase?  that seems like a problem all in itself.

some sort of buck converter/mppt is probably the future as i see it.

bob g

[paul_66]

"I have to use the turbine, that is there"
Is this something that will actually be built, assembled, and used?

There is a multitude of reasons to buy a factory made unit to do what needs done.

Transformer ratio must be suited to the wind speed.
If the system tries to start charging a battery when the wind is 4MPH, the system will not work much at all.

The 300V is at a wild frequency.  Many vary by over 400%.
Transformers have a design window of operating frequency, usually 50 or 60 or 400 HZ.
The chances of the alternator output HZ and transformer design HZ matching is very slim.

The output will be much higher with some form of fancy MPPT.
They are not exactly a DIY project for very many people.

If this is a paper and theory exercise, then a transformer to a rectifier is all you "need".
G-

Yes it has to be built, It's a college project. The college was approached by a company that has a customer with a turbine that wants the the voltage converted to 48DC to charge batteries. The turbine is already there. I have not seen it yet as it is about 4 hours drive, but I will do in the future. so At the moment I am being told I need to use a transformer. The company I am making this for want to use it as they are looking to get into the wind industry. They are a small plc company. So if it works ok they hope to get more work using the same design/system

[Opera House]

I hope you are not paying too much for your education because your lecturer is more than 30 years behind the times. TRANSFORNERS!!!!!  I look at a lot of these college projects and think ....What a joke. Your ideas should be leading the way.

[bob g]

personally i don't think your professor has a firm grasp on the problem, much less how best to address it.

also the manufacture ought to have their own engineering staff that is smart enough to realize that the use of
a simple transformer scheme isn't going to get them where they need to go.

having said that, this really doesn't surprise me though

the industry has a rich history of wild claims, flaky equipment, and good intentions

this company thinks it is going to take a shortcut by using free brains at a college to figure out how to make their
unit do something it was not designed to do?

they can certainly play around with transformer schemes all they like, but it will never be a successful design in my opinion
and as such is an exercise in futility.

this seems akin to someone bringing your professor a crystal set radio and wanting him to get you student to make it not only pickup
FM stations but do it in stereo using only some off the shelf thing like a transformer?  it is just not going to happen in my opinion.

actually i would rather try to convert the crystal set, as it can all be done on the bench and tested without having to climb a tower.

bob g

[TomW]

personally i don't think your professor has a firm grasp on the problem, much less how best to address it.

also the manufacture ought to have their own engineering staff that is smart enough to realize that the use of
a simple transformer scheme isn't going to get them where they need to go.

having said that, this really doesn't surprise me though

the industry has a rich history of wild claims, flaky equipment, and good intentions

this company thinks it is going to take a shortcut by using free brains at a college to figure out how to make their
unit do something it was not designed to do?

they can certainly play around with transformer schemes all they like, but it will never be a successful design in my opinion
and as such is an exercise in futility.

this seems akin to someone bringing your professor a crystal set radio and wanting him to get you student to make it not only pickup
FM stations but do it in stereo using only some off the shelf thing like a transformer?  it is just not going to happen in my opinion.

actually i would rather try to convert the crystal set, as it can all be done on the bench and tested without having to climb a tower.

bob g

I have to agree with bob here. Seems the cart is ahead of the horse here and the horse is standing on the load?

Just from skimming the thread.

Those that can do. Those that can't teach.

I just like that quip, it may or may not apply here.

Bottom line is you gotta jump through the hoops to get the hunk of paper at the end of the path.

Personally, I think you would learn a helluva lot more by being given the device and a free reign to solve the designated problem.

It might be a "trick" problem, too.

Tom

[ghurd]

I agree with Bob too

There are dozens of PhDs working on doing it well.
There are a few good ways to do it, and none of them is a transformer with a bridge.

The customer with a turbine who approached the company should look for another company.

As for a company wanting to market a good design that has the imposed limits, they may as well limit you to using sticks rocks boogies and spit.
They will not beat the Chinese company that made the turbine.

Just guessing because nobody can tell you anything specific until they know what you are starting with for the turbine, but I bet it is Chinese.

I think they have thrown you in over your head.
And then instead of throwing you a floatation device, they threw you a brick.
G-

[SparWeb]

Here's your graduate thesis, then:

www.rigel.ca/Xantrex_SW_Single_Install.pdf

Enjoy!

PS This is just the first one that comes handy.  Other systems may be more appropriate, either to the equipment on offer, or to the educational goals.

[ruddycrazy]

Haven't we missed something here, OK the turbine will do 300 volts AC unloaded, now go rectify the wild AC and hook it up to the 48 volt battery bank and then see if you still get 300 volts.........

[paul_66]

Thanks for all the replies. I am humbled by all the knowledge, to reply to an earlier post, the cut in speed of the turbine generator is 1.5 metres per second.

[paul_66]

it might be useful to know how many hz the wind gen runs at cutin?  or say at 6mph windspeed
if it is many poles maybe it can make 60hz at about a 6mph wind, if so transformers might well work ok?

the operating window for a 60hz transformer is up to 400hz and they will continue to function pretty well
way over that without much of a hit in efficiency.

i have spent some time working with transformers designed to run at 60hz on my 3phase test bed up to 600hz
and they work just fine

the problem i see with their use for this project is they really aren't well suited for the wild swing in voltage from cutin
to furling, you can match things for a specific speed/voltage but thing go out of optimum very quickly

tap changing as speed and voltage increase?  that seems like a problem all in itself.

some sort of buck converter/mppt is probably the future as i see it.

bob g

The cut in speed of the turbine generator is 1.5 metres per second. Is there anyway to make the voltage from the turbine a constant one so that it can then be stepped down to the same voltage every time?

[paul_66]

Here's your graduate thesis, then:

www.rigel.ca/Xantrex_SW_Single_Install.pdf

Enjoy!

PS This is just the first one that comes handy.  Other systems may be more appropriate, either to the equipment on offer, or to the educational goals.

How much would a system like this cost?

[paul_66]

What about using a buck transformer. It has multiple taps which can alter a range of voltage to a certain %

[ghurd]

Which tap will you use?

the problem i see with their use for this project is they really aren't well suited for the wild swing in voltage from cutin
to furling, you can match things for a specific speed/voltage but thing go out of optimum very quickly

tap changing as speed and voltage increase?  that seems like a problem all in itself.

[paul_66]

Which tap will you use?

the problem i see with their use for this project is they really aren't well suited for the wild swing in voltage from cutin
to furling, you can match things for a specific speed/voltage but thing go out of optimum very quickly

tap changing as speed and voltage increase?  that seems like a problem all in itself.

Hi Ghurd, forgive my stupity but what do you mean by that?

[ghurd]

I mean which tap will you use?

If you can decide which tap to use, then there is no need to have a transformer with multiple taps, because it would be better to start with a single output transformer.

The quote from BobG pretty much says one single tap is not a good idea because the input voltage is changing wildly, and making a device to switch taps is a major operation.

Which brings us back to-

There are a few good ways to do it, and none of them is a transformer with a bridge.

I am not saying it will not work.

The turbine can be destroyed if the device fails.
If something goes short circuit and burns out to open circuit,
or if something goes open circuit,
Frackers can tell you what happens,
http://fieldlines.com/board/index.php/topic,144696.0.html

G-

[Opera House]

The point should be that this is an educational project and you should be stretching your mind, not taking gigantic leaps backwards with transformers. Coming here for answers demonstrates a certain laziness.  Even if you don't have expertise in electronics it could be black boxed.  I was just working on a older Lambda LLS-5000 series power supply and noticed in the specs that it could be operated with a DC input from 240 to 350V DC.  The control inputs could do everything you want with a minimum of control electronics.

[paul_66]

The point should be that this is an educational project and you should be stretching your mind, not taking gigantic leaps backwards with transformers. Coming here for answers demonstrates a certain laziness.  Even if you don't have expertise in electronics it could be black boxed.  I was just working on a older Lambda LLS-5000 series power supply and noticed in the specs that it could be operated with a DC input from 240 to 350V DC.  The control inputs could do everything you want with a minimum of control electronics.

The whole propose of the project is to save money. If I go with an out of the box system then I won't be doing that. As said in my OP

[Hilltopgrange]

why not just rewind the turbines stator to suit 48v! or maybe even reconfigure the original windings! and forget about transformers, more details about the turbine would help.

Russell

[SparWeb]

Paul,

I just took a couple of minutes to re-read this thread, even though I've been following it for a while.  Good thing because I'm seeing the picture differently now that the information has had a second chance to pass through my brain.  I may be wrong on some of these points, but it looks like your situation is like this:

You are an undergraduate student with a work term to complete (we call it co-op in Canada), and
Your term supervisor has some experience with electromechanical systems, but only as an engineer, not as an electrician, and
Your term placed you at this PLC company so that they can get a clever guy to work on a troublesome wind turbine, and
They want the WT for public relations, but they don't know how to make it work by themselves, and
They also aren't willing pay an electrician with RE system experience, and
You have 5 months left before the end of your work term.

Am I close?

Sux2BU

Okay the situation isn't really that bad.  You have to take charge of your situation (not easy I know) by getting in touch with people that do the installing/matching/grid tying for a living, and wheedling all the advice they can give you.  Stay up late and work the phones to the USA if you have to.  And obviously you have to phone the manufacturer of the WT for their recommendations.  Then do your research on the available equipment on the market, and present what you think is appropriate to the PLC company as "option 1" for their consideration. 
Since you've already said they're probably going to refuse that, then you have in writing a "refusal to use off-the-shelf" equipment taken care of.  They have just taken 100% responsibility for all of your experiments afterward.

Then spend the remaining season having fun and tinkering on "Option 2"!

Well that sounds a bit cynical, but from time to time guys get put in work terms  with unrealistic expectations - either too high or too low.  You can still make the best of it.

The most important thing to do, if you really are in school to be an engineer, is to know that you have a job AND a responsibility.  The job is what I've just described.  The responsibility, however is DIFFERENT.  If you can rationally evaluate a situation and conclude that an error is being made, then you have a duty to your profession and society to make it known to your employer.  If you haven't sworn that oath yet, you'll be asked to in a couple of years' time.  The error may be of the safety hazard variety, or the economic waste variety, but your duty is pretty much the same.  It doesn't have to be a shouting match, or pointing of fingers, but when you sit down and "as an engineer" provide the option to install the system with qualified personnel, you are putting yourself in the position of warning about an impending failure.

I've made a couple of nasty assumptions about your situation, but I thought it important to explore the possiblity that you are surrounded by incompetence and inadvertently set up to take the blame.  Likely isn't as bad as I've made it sound.

PS: A neighbour of mine, just a few miles down the road, had a commercially installed WT that put out 240V 3-phase, and it was fed through transformers to step it down to 48V.  So it can be done, all you have to do is find the parts that will do it.  Since nobody's giving you directions, you're basically in charge of "system design" yourself.  At times you'll wear the engineer's hat and others you need the electrician's hat. 

[Jon Miller]

You need a buck convertor.

I know where one is and can handle 3kW.

Drop me a PM and i can forward details.

Regards

[oztules]

I'm at a complete loss as to why the folks here have so much difficulty understanding that this hv to transformer to rectifiers bit  has been done for a long time, and is VERY successful, and is much more reliable than any buck converter can hope to be with wild AC.

I can't navigate this new board at all, but in my diaries, there is a fairly detailed look at the AFRICAN WINDPOWER turbine here on Flinders Island. It has performed brilliantly for about 4-5 years now (except for the manufacturing faults as described in detail). It runs at a nominal 300volts ac, goes through a three phase transformer down to 48volts, and then to the batteries. done and simple. It has very very regularly done in excess of 24kwh per day for day after day after day. Yes it is in a good wind site, but it beats the pants of any other design I have seen for a nominal 1kw turbine. (after corrosion of the windings (not enough lacquer on them at manufacture) I rewound for about 1.5kw)

Paul.
It is critical to find out how many poles this turbine has, and it's rpm range. In the AWP instance, it is a 30 pole alternator. This is coupled to a 3.6m blade set. The rev range that is useable is quite great, but essentially, we monitor the input voltage/frequency, and when it approaches 180 volts or so, we cut in the transformer with ac solid state switches. (triac and an opto isolator) one phase wire is connected to the tranny all the time, and the other two phases are switched in at the step off voltage.
This is done so that the turbine can get up to a reasonable frequency before engaging the transformer. This makes the transformer part much simpler to deal with.... when the voltage drops below step off, we turn the two phases off until it recovers again..... do NOT use relays. They will rattle themselves to death quite quickly.

As soon as this step off is achieved, we simply rectify the 48v output and feed the batteries. They then feed the house inverter..... simple and very very sturdy.

I can't for the life of me understand all the fuss. I felt sure most of those commenting have read the stories.......maybe not worth the read?

If you have a very low pole count or very large rotor, the transformer will need to be a bit larger..... but remember, at low rpm, you don't need much transformer anyway, as the output will be low. As the power increases, the frequency will too, and the transformer will make a better fist of it. At very high rpm, the transformer will do even better.

Of all the stories I have read so far here, I have yet to see any small windmill system regularly put out this kind of kwh, or Hv controls run so free without magic smoke, or  very fancy protection

We have never done an efficiency test so I can't tell you what that might be, but it works very well... no question about it..... and it hurts me to say so, but it does better than my larger axial flux, which can do much much higher outputs, but the transformer loading with the iron stator seems to match the load better than I am able to do with the axial flux wound for 48v.

So, find out what the rpm and pole counts are likely to be, and this will dictate your choice of transformer core and windings.

Lastly, you get the opportunity of using a HV dump load for overspeed if you wish, and a LV dump for the batteries. at a pinch you can use both for redundancy.


If I can handle it ....... it aint rocket science.


...............oztules

edit... found one of the posts here    
http://www.otherpower.com/images/scimages/5171/awp_1.html

It goes into a fair bit of detail regarding the switching.
Heres part two if your desperate for some more reading   http://www.otherpower.com/images/scimages/5171/awp2a.html

(fixed the link. G-)

[paul_66]

I'm at a complete loss as to why the folks here have so much difficulty understanding that this hv to transformer to rectifiers bit  has been done for a long time, and is VERY successful, and is much more reliable than any buck converter can hope to be with wild AC.

I can't navigate this new board at all, but in my diaries, there is a fairly detailed look at the AFRICAN WINDPOWER turbine here on Flinders Island. It has performed brilliantly for about 4-5 years now (except for the manufacturing faults as described in detail). It runs at a nominal 300volts ac, goes through a three phase transformer down to 48volts, and then to the batteries. done and simple. It has very very regularly done in excess of 24kwh per day for day after day after day. Yes it is in a good wind site, but it beats the pants of any other design I have seen for a nominal 1kw turbine. (after corrosion of the windings (not enough lacquer on them at manufacture) I rewound for about 1.5kw)

Paul.
It is critical to find out how many poles this turbine has, and it's rpm range. In the AWP instance, it is a 30 pole alternator. This is coupled to a 3.6m blade set. The rev range that is useable is quite great, but essentially, we monitor the input voltage/frequency, and when it approaches 180 volts or so, we cut in the transformer with ac solid state switches. (triac and an opto isolator) one phase wire is connected to the tranny all the time, and the other two phases are switched in at the step off voltage.
This is done so that the turbine can get up to a reasonable frequency before engaging the transformer. This makes the transformer part much simpler to deal with.... when the voltage drops below step off, we turn the two phases off until it recovers again..... do NOT use relays. They will rattle themselves to death quite quickly.

As soon as this step off is achieved, we simply rectify the 48v output and feed the batteries. They then feed the house inverter..... simple and very very sturdy.

I can't for the life of me understand all the fuss. I felt sure most of those commenting have read the stories.......maybe not worth the read?

If you have a very low pole count or very large rotor, the transformer will need to be a bit larger..... but remember, at low rpm, you don't need much transformer anyway, as the output will be low. As the power increases, the frequency will too, and the transformer will make a better fist of it. At very high rpm, the transformer will do even better.

Of all the stories I have read so far here, I have yet to see any small windmill system regularly put out this kind of kwh, or Hv controls run so free without magic smoke, or  very fancy protection

We have never done an efficiency test so I can't tell you what that might be, but it works very well... no question about it..... and it hurts me to say so, but it does better than my larger axial flux, which can do much much higher outputs, but the transformer loading with the iron stator seems to match the load better than I am able to do with the axial flux wound for 48v.

So, find out what the rpm and pole counts are likely to be, and this will dictate your choice of transformer core and windings.

Lastly, you get the opportunity of using a HV dump load for overspeed if you wish, and a LV dump for the batteries. at a pinch you can use both for redundancy.


If I can handle it ....... it aint rocket science.


...............oztules

edit... found one of the posts here    
http://www.otherpower.com/images/scimages/5171/awp_1.html

It goes into a fair bit of detail regarding the switching.
Heres part two if your desperate for some more reading   http://www.otherpower.com/images/scimages/5171/awp2a.html

(fixed the link. G-)

The turbine frequency is 0 to 30 Hz . it is a 6kw turbine and will produce 6kw at 30hz

[oztules]

Then you will need a 3phase (?) transformer that will run 6kw@30hz. ( this is no small transformer!... and may be a project killer right there)

In theory, as we double the wind speed our frequency will double, but our input power will triple

This same transformer will need only to handle 1/8th of that 6 kw at 15hz...(  750 watts)... or 100 watts or less at 7hz.

As the frequency falls, the transformer may become less capable of it's power rating.... but the power drops exponentially faster than the power rating does.

So my take on it is that you design your transformer for max power realized, at that frequency (6kw@30hz), and as the power drops, although the power rating of the tranny drops, the actual power it is required to handle becomes disproportionately less.....we win...... (but gee it's a big tranny)

Nothing is simple with wind.... we may be able to use taps on the tranny to help match the load as well.... a bonus we don't usually get for free.


...........oztules