When turbines produce alternating current

quique

Okay here's another theory question for you guys.

I was able to witness the installation of a wind turbine at a friends house. I am a little confused with terms I originally thought I understood such as alternating current and direct-current. I understand alternating current is the most common type produced by electric companies because they use Generators to create current through spinning coils around the magnet. I understand that direct-current or continuous current is produced by the photoelectric effect of electrons running around a cell due to the energy absorbed from photons.

So Is this the reason why a wind turbine produces alternating current instead of direct-current?

One more thing, since the wind turbine produces alternating current this means the inverter actually works the opposite way by a converting that alternating current to direct or continuous current in order to charge a battery bank, correct?

solar_dave

Re: When turbines produce alternating current

I think you answered your own question.

because they use Generators to create current through spinning coils around the magnet.

BTW I think most of them rectify the current to DC with a rectifier bridge and then run it into a inverter to produce 60 cycle AC.

Cariboocoot

Re: When turbines produce alternating current

ALL generators produce alternating current. The difference is if, where, and how it is converted to Direct Current.

Old automotive generators were said to produce DC because the conversion took place inside as a function of the brushes on the commutator. These were replaced by alternators which produce AC but convert it (also inside) to DC by solid-state rectifiers.

With a wind (or hydro) turbine it is possible for it to send the power as AC down wires at high Voltage, then rectify it at the point of use. Or it can be rectified at the turbine head and sent to the point of use as DC.

It is easier to raise/lower Voltage with AC because all you need is a transformer. Becomes more complex with DC. Inevitably someone is going to mention that utilities also use DC for high Voltage long-distance transmission, which is true but not particularly relevant to our discussions here.

quique

Re: When turbines produce alternating current

So the inverter rectifies (which means "convert" three phase to single phase) and inverts to DC?

Cariboocoot

Re: When turbines produce alternating current

quique wrote: »

So the inverter rectifies (which means "convert" three phase to single phase) and inverts to DC?

No, an inverter does the opposite: converts DC to AC. By generating a stepped-Voltage output which mimics to a greater or lesser extent an AC output waveform (quality of which depends on the actual unit involved). This can be anywhere from pseudo-AC on/off square wave to utility quality (<3% THD) pure sine wave.

3 phase is a matter of AC output from multiple linked coils. As Voltage falls from peak across one coil it is rising on the next with the result looking on an oscilloscope as one sine wave 'chasing' after another (three distinct ones superimposed on the screen "120 degrees apart").

How extensively do you want to get in to this? It can take up quite a lot of paragraphs even in its simplest form.

quique

Re: When turbines produce alternating current

Rectifying refers to converting 3phase to 1phase, right?

Inverting refers to turning dc to ac.

And a wind turbine generates 3phase AC to 1phase AC by rectifying in the inverter. So what does the inverter do to convert ac to dc in order to charge the battery bank? What's that called?

Cariboocoot

Re: When turbines produce alternating current

Rectifying refers to converting AC to DC. Basic rectifier (diode) looks like this -->|-- and does about what you'd think: allows the positive AC 'pulses' to pass while 'blocking' the negative ones (the engineers are going to shoot me for that one). Net result: current flows in one direction.

In multiples the rectifiers will take the positive pulses from all points of the alternator and direct them all to the (+) terminal, while at the same time allow only the negative to the (-) terminal (okay, even I am cringing at my own explanation).

So you go from having two wires (for any given AC segment) with alternating positive and negative Voltage on each (in respect to the other wire) to two wires with single polarity:

+-+->|+ +
-+-+|<- -

(With a 'full wave' bridge rectifier circuit all the '+' get directed to one place and all the '-' to the opposite side. The difference has to do wit Voltage realized as a result.) In a power supply circuit there would be an electrolytic capacitor on the output to stabilize the Voltage. For battery charging the battery itself performs this function. (About a million variations on this basic theme are possible.)

But keep in mind that AC is not pulses like a square wave; it is a rising/falling Voltage level which crosses zero and changes polarity. This is why AC Voltage is measured as root mean square (a sort of 'weighted average' of the low and peak Voltage based on the curve of the sine wave). As long as the Voltage is positive in respect to the other wire it can be considered positive Voltage. I mention this because of the split phase standard of North America where the 'other wire' is sourced as zero by Earth bonding: the 'hot wire' switches polarity in respect to this zero potential and you actually see only half of the complete phase.

Blast; I'm wandering away from the essentials.

You can rectify single phase or three phase to DC: it doesn't matter how many 'pulse sources' you start with. The difference between the wind turbine charging and the inverter (or other utility/generator fed charger) is the number of AC phases to be rectified.

Cariboocoot

Re: When turbines produce alternating current

Here is a basic 3 phase alternator schematic. This is automotive type, with the source being electromagnetic instead of a permanent magnet (as is typical of a wind turbine).
Note the three stator windings (3 phase AC) and how they feed to six rectifiers to create DC.

quique

Re: When turbines produce alternating current

Sorry, to me it just looks like a drawing from Spy vs Spy!

I guess what I want to know is:

Sunlight ->PV -> dc -> batteries
Batteries -> INVERTER -> ac-1phase -> home

vs

Wind -> TURBINE -> ac-3 phase -> special inverter

A) ac-3phase -> Special Inverter -> ac-1 phase to home?

ac-3phase -> Special Inverter -> ac-1phase -> dc -> Batteries?

The inverter must do something special (Process A) to convert 3-phase to 1-phase AND something special( Process to convert AC to DC.
What is Process A and B?

waynefromnscanada

Re: When turbines produce alternating current

Not in the least intending to be, wanting to be perceived to be, interpreted as, or sounding like being insulting in any way, it would seem a course in basic electricity may be in order so as to permit better understanding of the help being offered.
That said:
Wind -> Turbine -> 3 phase AC -> Rectifier -> DC -> Charge controller -> battery bank -> inverter -> Household AC.
Sunlight -> PV panels -> DC -> Charge controller -> Battery Bank -> Inverter -> Household AC.

quique

Re: When turbines produce alternating current

Wayne

I totally agree, but I'm just curious. I'm not planning on studying this, I'm just trying to understand it. I'm a biochemist which is a far cry from electric engineering. But I would just like to understand some basic concepts without having to take a course in electricity which is easier said than done in Honduras.

And btw, as I have mentioned before in this forum, I am IMMENSELY appreciative and thankful of all the help I get.

Cariboocoot

Re: When turbines produce alternating current

Actually you are getting it!

PV's produce DC and can either be used to charge batteries or power a GT inverter directly.

Wind turbine produces AC, usually 3 phase, and can either be rectified to DC for charging batteries or for powering a GT inverter as above.

Although it is probably possible to take the 3 phase AC output and run a GT inverter designed to supply single phase to the home and grid, I'm not familiar with any system that does it that way. It would be complicated to change the varying Voltage, current, and frequency into varying current at fixed Voltage and frequency. The interim conversion to DC makes this much, much simpler.

quique

Re: When turbines produce alternating current

Oh ok because the inverter for the wind turbine has 3 wire input from the turbine (3-phase ac input) and it has:

2 terminals for DC output to battery bank

And

An ac plug which reads 240VAC output!

Cariboocoot

Re: When turbines produce alternating current

quique wrote: »

Oh ok because the inverter for the wind turbine has 3 wire input from the turbine (3-phase ac input) and it has:

2 terminals for DC output to battery bank

And

An ac plug which reads 240VAC output!

See that one I put in bold? Sort of indicates the rectifying is going on inside the inverter. Got a make and model for it? Does it require batteries or are they optional?

We have seen various "all in one" machines (usually incorporating a solar charge controller) before. They tend to come up a bit short on performance in one area or another.

quique

Re: When turbines produce alternating current

Nah, he got it in china.

But so he will be getting 1phase ac from that plug output? But only when the wind is blowing? Like the GT inverters?

Cariboocoot

Re: When turbines produce alternating current

quique wrote: »

Nah, he got it in china.

But so he will be getting 1phase ac from that plug output? But only when the wind is blowing? Like the GT inverters?

Yes, the output would be single phase: you can't get 3 phase on any less than 3 wires (not including neutral and/or ground).

If there's no other source (such as batteries or PV) to power the inverter it will only output when the wind is blowing.

Just love that Chinese engineering. Some of the designs ... well you just have to shake your head and walk away. In some cases run away. There's a good reason to be leery of that stuff.

BB.

Re: When turbines produce alternating current

Part of the confusion is that we describe everything as "piece parts" and the actual devices may contain many of the pieces (functional blocks) to make, what appears to be, an "all in one" unit.

So, understand the individual functional blocks first--Then you can see how you can package two or more blocks into a handy retail appliance.

I think, where you are stuck here is with the Rectifier (one to six diodes). It is an important component, but it can be pretty small and easy to over look.

Rectifiers can be in the alternator (such as your car's alternator). Or the can be a separate block, usually mounted on a heat sink. There are so many versions and packaging options, it can be very easy to miss the rectifier.

Also, a Rectifier is (sort of) the exact oposite of an AC Inverter...

The Rectifier takes AC power (one or poly phase) and converts it to DC current (usually with some pulsing). An AC Inverter takes DC power and coverts it to AC power (one or poly phase, etc.).

The difference is a rectifier can be a very simple device. Whereas an AC inverter is usually pretty complex, and usually includes some sort of transformer so that it can take 12 VDC and output 120 VAC.

If you want to get really confused, there are active electronic rectifiers that are called synchronous rectifiers... These are very similar to running an AC Inverter "backwards". There are reasons people do this, one is Diodes always have around 0.2 to 1.0+ volts of drop, and this wastes energy. A synchronous rectifier uses FET switching (field effect transistors) which can be much more efficient (less energy loss during power conversion).

You have to be really flexible with your understanding of electronics... Almost every simple electrical circuit can have multiple ways of accomplishing the same thing. There is no "one way" that things are done. Some of them really are mind blowing (like taking a standard off grid TSW AC inverter and connecting it to a standard Grid Tied Inverter--The GT Inverter can push energy backwards through the OG Inverter and actually recharge the DC Battery bank (i.e., synchronous rectification from a standard AC Inverter). It blew my mind when I first heard of this being done a few years ago as a way to use a Skystream GT Based wind turbine to work with an off grid home.

-Bill

ggunn

Re: When turbines produce alternating current

quique wrote: »

The inverter must do something special (Process A) to convert 3-phase to 1-phase AND something special( Process to convert AC to DC.
What is Process A and B?

The output of a wind generator is converted (rectified) from three phase AC to DC, not from three phase AC to single phase AC. The reason it has to go through this step is that the frequency of the AC from a wind generator is dictated by the rotational speed of the turbine, which changes all the time. The DC is converted to 60Hz synchronous AC by an inverter for connection to the grid.

quique

Re: When turbines produce alternating current

Ok one more thing i want to know...

the turbine is rated at nominal 1000W. Its voltage however is rated in

offgrid 24-48vdc
ongrid 48/110/180vdc

First question; is this because if connected to the grid, the inverter will pull as much as it can whereas when connected to the battery bank itll produce just enough to fill up the batteries?

Second question; we've had a voltmeter between 2 of the 3 wires on it and its been reading between 20 and up to 80Vdc at times. What should the amperage be doing? At 20V should it be up and at 80V should it go down.

Cariboocoot

Re: When turbines produce alternating current

Your question can't really be answered because none of us designed the system. In any given circuit of this complexity Voltage and current will vary depending on what point it is measured at.

So the turbine itself may produce up to 80 Volts across any one of the phases (regulated inside the master unit) and its total power potential may be limited to 1000 Watts and as such the current from the turbine may be no more than 5 Amps per phase under those circumstances (tricky relationship between V, A, and W when dealing with 3 phase).

They may alter the limits or phase wiring connections when used for on or off grid as needed.

Suffice to say there's always more than one way to do any of this stuff, so you can't really nail it down to "all (turbines/controllers/inverters) work like this".

inetdog

Re: When turbines produce alternating current

quique wrote: »

Ok one more thing i want to know...

the turbine is rated at nominal 1000W. Its voltage however is rated in

offgrid 24-48vdc
ongrid 48/110/180vdc

First question; is this because if connected to the grid, the inverter will pull as much as it can whereas when connected to the battery bank itll produce just enough to fill up the batteries?

Second question; we've had a voltmeter between 2 of the 3 wires on it and its been reading between 20 and up to 80Vdc at times. What should the amperage be doing? At 20V should it be up and at 80V should it go down.

First answer: It assumes that the GTI will have some sort of MPPT type variable voltage input and so can use the higher input voltages while a PWM battery charger will be most efficient with in the incoming DC as low as possible while still supplying enough voltage for all stages of charging.

Second answer: The amperage will depend on what kind of load you put on it. If you have a constant resistance load, then the current will go up as the voltage goes up.
If you have a constant power load, like some motors or an MPPT controller in Absorb, then the current needed to deliver that same amount of power will go down as the voltage goes up

In general for a turbine the voltage and the current available both go up as the speed increases.