Fusing wind turbine in hybrid system

[kouts5]

Hi people, newbie here. Im going to add a 500W / 24V wind turbine, on the 1000W PV off grid system, so batteries can get some extra juice during the night.
I know that hots should be fused between rectifier(or)/controller and the battery system, and between the battery system and inverter.On the internet, I've seen people adding 3 fuses between the wind turbine and the rectifier/controller. So my question is: What is the point of fusing on that spot. Is it necessary and why? What happens if one fuse accidentally goes off? Will the turbine run freely and get damaged?


I did a quick drawing to help you understand.Thanks for your time.

 

[svetz]

Welcome to the forums!

This seemed like a fairly advanced question so I've moved it to the Wind section where hopefully someone can answer it!

 

[FilterGuy]

I do not have a lot of direct experience with wind turbines, but I am having a hard time coming up with a scenario where those fuses are useful....

Let's look at the possible failure modes where the fuses might help.


Failure modes:
1) protecting the turbine wires from over-current from the turbine
Given the position of the fuses, they can not protect the turbine wires from a short. They would have to be next to the turbine to do this.

2) Keeping the turbine from producing so much current it burns itself out.
I don't think that is possible (at least for smaller turbines). In fact, a lot of systems short the turbine wires when they need to do a full break in high winds. If a turbine could overpower itself, shorting the wires would do it.

3) Protecting the 3-phase rectifier from over-current from the wind turbine
The bridge rectifier should be sized considerably larger than the max current that would ever come from the turbine.... making the fuses unnecessary for this purpose.

4) Protecting the wires to the turbine (and the turbine?) from over-current from the battery.
Could the rectifier fail in a way that allows battery current to dump onto the 3-phase line? I guess if the right diodes failed as a short as shown below it could, but since diodes usually fail 'open' this seems extremely unlikely. Furthermore:

• If only one diode failed as a short, there would be no battery back-current. (This line was added in an edit)
• If all the diodes failed as a short, it would short the battery and blow the battery fuse.
• If both diodes on one phase of the AC-input failed as a short, it would short the battery and blow the battery fuse.

Edit: Updated Pic to show short circuit path better.



Note: There are a lot of wind turbine systems that directly charge lead-acid batteries as shown above. However, a more sophisticated system might put the controller between the rectifier and the battery. In that case it seems like it would be nearly impossible to dump battery current on the turbine wires.


Conclusion: I don't think the fuses do any good and, as you point out, if they blow the windmill would be allowed to freewheel...damaging the windmill.

 

[kouts5]

Thank you @FilterGuy for the thorough analysis. That was helpful!