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Wind farm application

Wind farm application

Wind farm application

(OP)
Do people use current limiting fuses in conjunction with switchgear to be able to tackle higher fault currents in Wind Farm applications? If so, are there any disadvantages that make them not very palatable?

Thanks

RE: Wind farm application

What higher fault currents?  Where?

RE: Wind farm application

If the switchgear is listed/tested with such devices, yes. If not you can use them but the short circuit rating of the switchgear remains what is listed on its nameplate by the mfr.

 

Rafiq Bulsara
http://www.srengineersct.com

RE: Wind farm application

In any case, you cannot install a switchgear at a point where available SCC is higher than its listed rating.

In other words, you cannot reduce the calculated available SCC, because you are using a current limiting device upstream. This method is not accepted by any recognized standards. I presume that is what you meant my "tackling" "higher" fault currents.

Rafiq Bulsara
http://www.srengineersct.com

RE: Wind farm application

Generators do not do well when single phasing occurs such as when one fuse in a disconnect blows.  Protective relays that sense single phasing or negative sequence currents can protect the equipment if they trip a breaker or contactor   to isolate the equipment.

The breaker or contactor has to be rated for the maximum short circuit current.

 

RE: Wind farm application

(OP)
Say you have 50kA SCC levels. Can you use 25kA rated padmount switchgear along with a current limiting fuses by the transfomer at the turbine?

Single phasing is a good point, but probably can be taken care of using a relay to operate the switchgear when this occurs.

RE: Wind farm application

No.  If you have 50kA, you need 50kA gear.  At lower voltages there are series rated combinations where the fuse in conjunction with what would otherwise be lower rated equipment provides a higher rating, but this is achieved through testing lab certification, not by looking at fuse let-through currents.  At medium voltage and higher I've never seen any series ratings.

RE: Wind farm application

ABB and one other supplier (used to be GEC) have medium voltage current limiters that react in sub-cycle times on high fault currents.  ABB calls it an Is-Limiter.

The typical application is to protect under rated equipment when system additions raise the short circuit levels. We ahve applied them in parallel with a reactor.  If a high fault current occurs, the limiter opens and places the reactor in the circuit.

They are probably too expensive for your application.  
 

RE: Wind farm application

What is there to comment on?  It reduces let-through energy but doesn't do anything about equipment ratings.  Great for arc-flash hazard analysis, but not helpful for equipment ratings.

On the other hand, you've never answered my original question, what higher fault currents?  You simply don't have that much fault current on the 690V side of the tower transformers, less than 44kA, and the fault current on the high side is heavily influenced by the connection to the transmission system rather than any contribution from the towers.

RE: Wind farm application

(OP)
It's not on the 690V side of the transformer. It's on the 35kV side.What do you mean by not helpful for equipment ratings? Are you talking about the transformer or the switchgear equipment?

This question is not for a problem I am trying to fix at a wind farm. It is more out of curiosity.

So if there is a chance of 50kA fault levels which are possibly very very rare, can a current limiting fuse in conjunction with the 25kA rated switchgear solve the problem than paying a premium for 50kA switchgear.

RE: Wind farm application

No it cannot.

RE: Wind farm application

The Clip fuses I mentioned above might be configured to protect the 25 kA equipemtn.  But the cost would be several times  the 50 kA equipment premium.  For new 15 kV new switchgear I remember the cost was the same range as a 1000 MVA circuit breaker.

The Clip technology is a  different than a standard current limiting fuse.  Instead of a thermal fuse element, it has a solid state sensor that measures current and rate of change of current.  It only triggers if the fault current is close to or above the setting, say 22 kA for your hypothetical 25 kA equipmetn.  Current interruption is done by triggering shaped charge explosives that severe a bus bar, transferring the current to a current limiting fuse.

This technology avoids some of the issues of series rating, but now all.

Is this "legal"?  Depends on the AHJ in your area. If the equipment has to be UL listed or equivalent, there will be a problem.  Also, depending on your layout, you might need one for every generator pad mount transformer which makes it not economical.

 

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