Status Dutch Scirocco

[Frank Janssens]

Thanks to the help of this forum, the Scirocco/EOLTEC is now running for about 2,5 years in NOORDWIJK (Netherlands) and I want to share some of our experience.

a) Due to local regulations the set up of the mast is far from optimal and ressembles the Eoltec Demo at Nice but we can live with this (we have to :bigsmile:). The prevailing wind direction at the coast here is W-SW but that direction is partly screened of by trees. From the N-NO direction the wind comes in freely over the flower fields.
We estimate to have a yearly return of 6000kWh.
b) The mast had to go through the roof of a barn, which I think, raises its lower first bending frequency slightly above 90 RPM. So we have a nice humming sound when the scirocco starts and that disappears when it speeds up. At beaufort 8,5 the system we shut the system down with the mechanical brake as a precaution. (One experience with an howling sirocco was enough). Theoretically the system can withstand 12 Beaufort (Orkney Islands) but we feel safer that way as the combination of heavy turbulence (low mast/ vicinity of objects)and restricted quality of the guys are adverse conditions.

c) On the Aurora PVI-7200 WBI

- In our working conditions, supplementary cooling on the cooling fins is needed (dia 1). The dimensioning of the cooling fins is unchanged since the model that we bought. I seem to remember that also other users recommended this (Logan Bryce ?)

-At the time the WBI was still produced by Magnetek and we understand that there were several modifications since that production went to Power-one. The control unit of the diversion load has been added , the schematics we had showed a "brake" (optional) which is now the "diversion load" as a protection against grid failure. I also wonder if tin our box here is anything like the "crowbar"which is shown in the power-one manuals Version 4.

Anyway, our main safety protection is the thermal breaker which was experimentally adjusted to trip before any of the fuses in the WBI trips. The original Busemann fuses (expensive) were replaced by standard 16 A fuses and placed outside the WBI through the slot foreseen for the optional brake : third one from the left on dia2 and in the current version used for the diversion load.

- The clip-in connectors for the incoming bulk wind seem to give occasionally bad contact, causing a going-up and down speed of the turbine. So parker screws were added (dia2) to ensure a good contact. Has anyone experienced something similar ?

d) At this moment, our system is not well protected against grid failure which luckily for us, is a rare event. We would like to have a solution that shuts the system down BEFORE the WBI , preferably by activating the thermal breaker. Is that a good idea ?Any suggestions ?
The only servicing adress for our area by Power-one is one in Belgium. However Cor Van Houtem (draaistroom) seems to be an expert for these products.


Best greetings to all the members of this wonderfull forum,
Frank Janssens

[Rob Beckers]

Hi Frank,

As to the thermal breaker vs. the fuses: The more I think about it, the more I'm leaning towards replacing the 20A fuses with something much larger, such as 30 or 35A. The thermal breaker already provides overcurrent control, so the fuses are not really needed (might even replace them with copper pipe of the same size, but that tends to set off inspectors). This resolves the scenario where a single fuse blows, and there's not enough wind/power to trip the thermal breaker. This case will break the alternator, given enough time, due to the vibration from running single-phase. The thermal breaker on the other hand will switch off all three phases in case of overcurrent, and it has a lower trip-point when running single-phase.

The UK distributor/installer is using a very fast acting regular triple-breaker (non-thermal), and over there they do replace the fuses with copper tube pieces. So the credit for the idea goes to them.

-RoB-

[Frank Janssens]

tx for the reaction, we are thinking along the same lines :
Better ONE robust safety measure as several ones that can possibly have an bad interference. The logical place for protection of the electrical installation is to disconnect the bulk current BEFORE (in front off) the WBI. The sirocco runs then freely, no load on the tower, and one has plenty of time to operate the mechanical brake.
Maybe the problem is that most electrical devices come with their own set of fuses which for the application to 3phase windturbines rather INTRODUCES a certain risk.
It will not be easy to convince the manufacturers to deliver a product without fuses.
Hence we have to go to ad hoc solutions.
I guess y're referring to BJRE in the UK ? they seem to have a lot of experience.

Do you know of a protection against grid failure that uses also this principle ?
I mean disconnecting the bulk input in front of the WBI ? (In the current set-up this
protection comes from the diversion load). Is this possible at all ?

Frank

[Rob Beckers]

Yeah, BJRE uses fast triple-pole breakers and no fuses.

There shouldn't be any need to protect against grid failure: The Scirocco will quite happily run unloaded (no grid) for any amount of time. Gets a bit noisier than usual, because the blades run at stall angle (so what you hear is turbulent air spilling off the blades), but it's perfectly safe and RPM stays under 250.

-RoB-

[Frank Janssens]

Hi Rob, are you sure that grid failure can not do any harm to the system (turbine or electrical devices) ? .I do not understand this very well.
The "Installation and operator's manual " of Power-one Rev.4 (PVI-7200/4000/2500) gives one p.10 the mode GRID FAIL where:

the WBI is operative, WBI Output Voltage Vdc>530 ,Diversion Load ON.

This makes sense to me, the turbine delivers still wild current (not unloaded) , which is converted but cannot be delivered to the grid (which is not there). So, the V builds up above 530 V (at normal wind speeds) and the DIVERSION LOAD (ON !) in the (new) WBI has to take care of this, protects the WBI.
According to this, a grid failure does not imply that the sirocco runs unloaded (as if the thermal breakers had been activeted).
Is this correct ?
Frank

[Rob Beckers]

The centrifugal pitch control mechanism of the Scirocco turbine will pitch the blades to stall angle at around 245 RPM, regardless of load or wind speed. With the RPM fixed the maximum output voltage of the alternator is fixed as well, and peaks around 350V DC. It simply won't go any higher. No diversion load required.

The net result is that it's perfectly safe to run the Scirocco unloaded. The pitch control mechanism is very simple, very few moving parts, and very reliable. I know of Sciroccos that ran for months without any load with no consequence. It's designed to allow this.

-RoB-

[Frank Janssens]

We agree that unloaded running of the scirocco is perfectly safe.
The question is, does this happen automaticaly when the grid fails ??.
Do you claim that for the scirocco,a supplementary protection is not needed and that no diversion load is required ? (That would solve my problem :) !) .

The thread 3 phases AC dump load started by Rob Littiken 21/04/10 about the dimensioning of the dump(diversion) load originated also from the worry about grid failure
( + too much power which is not a concern for scirocco)

Maybe my messages are not clear ?

frank

[Rob Beckers]

Frank, yes, it's automatic when the grid fails, or the inverter fails, or for any other reason.

The blade re-pitching is mechanical, it has nothing to do with the electrical part or the load. It's simply based on RPM: Two fly-weights move outward based on the RPM of the blades, and once the RPM is sufficient to overcome the force of a spring in there it will re-pitch the blades to stall angle. Stalling the blades sheds the power in the wind, so it won't speed up. This keeps maximum RPM within a very narrow band just over 245 RPM.

That is why I like the Scirocco so much; there is no running away of the turbine, regardless of the load or wind speed (well, up to 215 km/h, after that you're on your own, but by then your house is coming apart and you don't worry about the turbine any more). :sick:

-RoB-

[Frank Janssens]

I summarize my understanding in the attachement.
When the system is open UPSTREAM of the PVI (A) , the PMG runs freely, the mechanical energy is not converted to electrical as there is no way out for the current.
Aready for moderate winds, the scirocco goes to its ~250 max RPM but internally the PMG is under tension (moving conductors in a magnetic field). This tension should be 430 V and the parts are dimensioned such this causes no spikes. The PVI box (light green) sees no tension at all.
For a grid failure, the cut is at B. Again, no current can leave the system, the PMG runs also freely,but the PVI's are under tension. As long as there no spikes in the incoming tension (max speed under control by the the mechanical system) the PVI's are fine and there is no need for a diversion load. In the water analogy in the lower part of the picture, the middle box is empty in case A and completely filled in case B. No water goes into the river in both cases.
I tried to upload 2 short movies (.mov) showing the transition to free running in both cases but these file were not accepted (?). The noise level goes down in both cases while the scirocco speeds up.
At a new startup, there was a distinction. In case B the fuses to the grid blew open what confirms the tensions in the PVI-3600.

So, I understand that Aurora recommends a diversion load for protection of their devices
(set at 600V - for example, a max value for electrolytic capacitors ?) as they can be coupled to turbines with a less robust (mechanical) max speed control.

A last comment: the PVI's detect the presence of the grid and display this neatly. This implies that their is some grid current flowing in the PVI's. We deliver also power to the grid, so in the opposite direction. Modern fuses usually contain diodes that protect the grid, they operate only in one direction and we have current flowing both ways.
The solution was to revert to the older type which is just a wire of the correct thickness which always works both ways.
Maybe the understanding is wrong but in practice this step was badly needed.

Frank

[Rob Beckers]

Frank, movies can't be uploaded due to their size, and the lack of bandwidth to stream them to viewers. Instead, you can upload movies to a file sharing site such as YouTube, and place a link to it in the forum message. The forum software recognizes many file sharing sites and will automagically insert an inline media player instead of the link.

As long as you read "tension" as "voltage" then, yes, your understanding is correct. In the mechanical sense there is no torque/tension on the alternator by the blades when the turbine is not connected to the grid. It's free-wheeling. There is voltage, but no current. The voltage cannot exceed 600V DC due to the limited RPM (voltage of an alternator is linear with RPM). It should stabilize in the high 300's Volt range, giving you a wide margin.

Connecting to the grid should not blow the fuses in the wind box. The grid can, and over here does, go down every now and then. When it comes back the inverter should reconnect seamlessly, without blowing fuses. As to those fuses in the wind box: You might as well replace them with very large ones, say 30A or 35A each. There already is overcurrent protection in the form of the thermal breaker, and all the fuses do is increase the chance of blowing just one, making the alternator run single-phase and break. The British distributor no longer uses these fuses at all (for that reason), I'm thinking of doing the same.

Most fuses that I know/use are simple mechanical devices without any electronics. They are not uni-directional. Keep in mind that AC voltage/current by its very nature will change polarity and direction many times a second.

-RoB-