Turbine Overcurrent Protection

[blueEnergy]

The drawing represents a simplified schematic for a  12V, 500W turbine charging a battery with an inverter.  We are using a Xantrex C40 in diversion mode for our charge controller.  Our max current from the turbine should never exceed 45 A.  We are using a disconnect switch that, when it is opened, shorts the negative and positive to the turbine.  We have a 110A breaker to the inverter, and a 60A breaker on the line to the turbine. The 60A breaker is sized so that current from the turbine can never open the breaker, but a short on this line would open the breaker with current surge from the battery.  The catch with turbines is that a breaker open circuits the circuit, which causes the turbine to overspin.  Ideally we would want some sort of a breaker that, when it opens it closes another switch which shorts the connection.  We haven't found any off-the-shelf device (Does anyone know of any?).  The thing that concerns us with the current setup is this:

If there is a short on the line between the 60A breaker and the turbine, the 60A breaker will flip, open circuiting the turbine.  However, if the cause of the surge is a short, then this would also break the turbine, so it seems as though everything is fine.  However, overcurrent devices are used to protect the wiring, equipment, and (I guess) people.  The wire should be sized above the rating of your overcurrent protection.  However, how do we know what value current will actually brake the turbine in a short so that we can size our wires properly?  How do code inspected systems properly address this issue?

Thanks a lot!

bE

[wpowokal]

Hi bE, your first question while valid is one I don't cater for, I put it in the catagory of what if I get hit by a bus tomorrow.

However you could bring the feed from your turbine through a contactors normally close contacts. On the normally open contacts short the turbine.

Use a two pole breaker, one pole for turbine current with the second energising the coil on the contactor. Thus when/if circuit breaker opens so too does the contactor, and applies a short to the turbine.

Your second question, if a short is aplied to your turbine to slow/stop it, any over current will only be brief and should not cause any cable damage assuming the cable was correctly sized in the first place.

In case you need it this is just one site that gives cable ratings, not the only or the best IMHO.

http://www.windsun.com/Hardware/Wire_Table.htm

But I suspect you already have this sused out.

Allan down under

[wpowokal]

bE did my responce adequatly answer your question?

I could explain DC V AC breakers etc, but suspect you are already faily familuar.

allan down under

[blueEnergy]

Thanks for your reply Allan,

Yeah, we are going to go up and measure what the short circuit current is on our turbine, and check the surge specs on the wire, but I imagine that you are correct - we don't need to worry about a slight surge damaging the wire insulation.  (We will have #6 wire, rated for 65 A before derating, for a 500W, 12V turbine).

Have you ever used normally open relays to short-circuit the turbine if a breaker flips?  If so, do you have the specs?

Also, I would be curious to know what info you have on AC vs DC breakers.  My understanding is that DC rated breakers have a much higher Arc rating than AC - but here in rural Nicaragua DC rated breakers are hard to come by...

Thanks a lot,

bE