Micro Hydro Grid Connection

[EJames]

Hi there,

I'm new to this and as you will see from the stupid questions I ask I am struggling with the electrical side of things.

I'm looking at a hydro scheme and I'm confused about the power generation and grid connection under G83. I have a net head of around 50m and a flow of around 40l/s (still informal agreement with SEPA from a FDC I done but I don't expect many issues with it) so can easily generate 11kW for G83 grid connection. I understand under G83 to connect 11kW I would need 3 phase at maximum of 16amps per phase.

Various questions

1) Just to clarify my understanding of the phase system: 3 phase at 16 amps is 3*230volts * 16amps = 11kW

1a) I am aware of the RMS and 400 volts thing but don't really understand what that means.

2) Could anyone advise on the easiest/best/cheapest way to connect to the grid?

As far as I can tell the easiest way is through a type tested grid tie inverter. However, that will need a DC input, so if my turbine is generating AC I will need a rectifier.

3) Does the turbine and the inverter need to be type tested or is it just the inverter?

Thanks in advance

[guydewdney]

1) - yes - its the current thats limited - not the power. Talk to your dno - they might allow more (they did for me)
1a) RMS and 400v - dont understand the Q

2)Wind inverter connected to pma generator or a back-feeding an inverter drive. I use a pma connected to a 'wind interface' which changes it from three phase ac to DC, and smooths it.

3) afaik - just the inverter. But FITs paperwork for hydro is a whole thing unto itself.

[EJames]

Thanks

1a) I've read stuff about the root mean square of 400 being 230 and if you measure phase to phase its 400 volts but because of the neutral/earth you have to measure from phase to neutral/earth and this comes to 230. It doesn't matter really, would just like to understand it - will do a bit more research.

2) Not sure I follow No2. So I would have a hydro turbine generating 3 phase AC connected to a 'wind interface' (such as the Aurora) which outputs smooth DC. This would then connect to a G83 type tested wind inverter (such as a windy/sunnyboy range) which changes the DC back to 3 phase AC for grid connection?

[Philip R]

The relationship between phase voltage of 230V ( Line to neutral) to Line voltage of 400V ( Line to line) is the square root of 3. It has nothing to do with RMS which happen to be the square root of 2.

draw yourself a phasor diagram, three lines 120 degrees displaced from eash other. Each 2.3 cm long( ".3 cm represents 230 volts).

Now measure the distance between the ends of each phasor, they should be 4.0cm apart. That is your 400 Volts!!

Not telling you any more, you might try and ascertain the vector group of your local distribution network transformer!!

PhilipR

[guydewdney]

2) As far as I can see, theres two basic methods of grid connection with hydro. Its very very similar to wind, as you have a spinning thing, that spins at different speeds, and needs controlling not to go over speed.

The first method is as you describe - its a permenant magnet (or field excited) generator / alternator (PMA). Any standalone generator off a diesel genny would work for example. I use a super slow speed generator, so I dont have to gear it up to silly speeds (my wheel turns at 5rpm, a diesel genny spins at 1500 rpm). My PMA spins at 300rpm. I did this for noise reasons too - as the system is inside my house, next to the living room. This system produces 'wild' 3 phase AC - ie uncontrolled frequency and voltage, allowing the turbine / wheel to do its thing. This wild AC is fed to a rectumfrier, and smoothed (and voltage limited with an integrated dump load). The DC is then fed to a grid tie inverter (G83 rated) and bobs yer mothers live in lover.


The second method is simpler in ways, but requires a higher speed generator. There are commonly available 'inverter drives' or 'variable frequency drives', same thing. Basically, they are normally used to drive 3 phase motors in industrial applications at variable speeds. However, some clever spark realised you can use them as a brake - often on long downhill conveyors by telling the motor to spin at a slightly slower speed than it is trying to go at, creating a braking effect. This energy is then back fed into the grid, and is used (in an industrial application) to reduce to power requirement of the entire plant. In our case, the power would be exported. However, you need a 3 phase motor spinnign at quite a high speed in comparison to method #1 to use this system economically. Its more applicable to a turbine than a waterwheel.


Why all the questions about RMS and 400v? I take it you have three phase? The G83 rules are per-phase - so its whatever your local voltage is - but if you talk to your DNO. you might well be allowed more under G83 - I have: 3.6kw+2kw on phase #1 then 3.6kw+2kw on phase #2 then 4.2kw solar on phase #3, which is 15.4kw all on G83 (thanks to a nice bloke at western power)

I hope that helps.

[Richard Owen]

3) Does the turbine .....

As Guy mentions above you can either generate AC direct into the grid or you can generate AC and rectify it to DC and then invert it back to AC into the grid. Or, I suppose, you could generate DC from the turbine and then invert to AC.

In addition to other things to think about:

If you connect an AC generator to the grid you need to have a load of custom control gear to get it on and off the grid as per the G83/1 specification. If you convert to DC and then to the grid via an inverter, all that work is done for you.

If you connect an AC generator to the grid and the water supply falls, the generator will turn into a motor and will pull energy from the grid. Which means, you need more control gear to sense which direction the current is flowing in and take the appropriate action. If you convert to DC and then use an inverter to make grid AC, the inverter will continue to convert whatever the turbine makes irrespective of how much or how little.

[guydewdney]

If you connect an AC generator to the grid you need to have a load of custom control gear

Did I say economically viable methods?

[Ted]

AC current and voltage is described, over time, as a sine wave. See http://www.animations.physics.unsw.edu.au/jw/power.html and http://en.wikipedia.org/wiki/Alternating_current#Mathematics_of_AC_voltages but don't worry too much if you don't understand it.

Are you planning to apply for the Feed-in Tariff? Check out http://www.microhydroassociation.co.uk

[noah]

With a head of 50m you should not need to worry much about speed increases. In that case I would advise an induction generator system. The great advantage of the induction system is that the generator is pretty much immune to overspeed damage. To comply with G83 means buying an off the shelf system: it`s possible to design something yourself and make it work (I could put together a workable 11kw system using a secondhand motor/generator and a few sensors/contactors for a few hundred. However doing that to G83 standards and, more problematically, proving it requires a fair bit of knowledge, specialised components and access to testing gear).
I would avoid jnverters if possible- the electronics involved are vastly more complex.
I have a 10.5 kw crossflow turbine using this system.

http://s990.photobucket.com/albums/af26/brianfaux/Turbine/

[clivejo]

Nice setup Noah.  Got me stumped thought, I found the light switch but I cant find the "go" button  

Some hydro porn I found, looks like its even got heating in it !