DC protection

[johndaniel]

I am currently working on solid state transformer protection system design. I have to design dc protection of 400 Volt dc link but constraint is that I can not use circuit breaker for protection as DC circuit breaker is expensive. Any ideas and suggestions are welcome

 

[davidbeach]

Fuses?

 

[johndaniel]

My DC link current is an order of 1500 A. I did not found any dc fuse for this large rating. Could you suggest any product or company which make fuses of this rating or beyond.

Thanks

 

[MikiBg]

Maybe you can split your link (outgoing) on several smaller in parallel, each protected with one fuse link or use several fuse links in parallel for one 1500A outgoing? Don't know is it acceptable from regulations and codes point of view.

 

[ScottyUK]

Ferraz have some pretty big fuses available. For example, their A60X semiconductor fuses go up to 2000A.

 

[johndaniel]

@ScottyUK: I have one doubt. Can I use AC fuses for dc system protection?

 

[ScottyUK]

Sorry John, missed that. Not sure how big their DC fuses go - there are certainly some in the 1000A range. Maybe a call to their apps guys would be worthwhile?

 

[ppedUK]

Check out Bussmann square bodied fuses. They are normally AC rated, but can be de-rated for DC application. I think they go up to 1250Vac, but their on-line technical manuals will tell you what voltage they can be used on. It's 30 years since I worked on heavy current DC, but I remember that for high current rectifier sets, there were many fuses (all of the same rating) in parallel across a pair of tinned copper bars. Obviously with this set up, a fault or overload would take out all the fuses, one after the other (and there were a lot of them), but for 1500A I don't think you will have too many in parallel.

Remember also that that the breaking capacity is also reduced for use DC systems. BS88 and IEC60269 fuses can be used on DC, but I'm not sure what voltage they go up to.

 

[ScottyUK]

SIBA's Photovoltaic range manages 400A at 1000V DC.

Mersen (Ferraz) can manage 1600A at 750V DC if you can accept the ultra-fast characteristic.

 

[johndaniel]

Thanks @ ppedUK and @ ScottyUK for your invaluable suggestions.