15kV Fuse

[jwparker]

Im trying to spec a 12.47kV load break switch with a 600A fuse, or close to it. Finding the 600A switch is easy but I cant seem to find a 600A fuse/fuse holder. Only 540A but requires 800A holder, what am I missing?

 

[rbulsara]

You need to use double barrel fuse holders and two fuses-300A each. Use only factory tested/approved assemblies.




Rafiq Bulsara

http://www.srengineersct.com

 

[jghrist]

Padmount? Pole-mount? Metal-enclosed? Air break? Vacuum? SF6? Current-limiting fuse? Power fuse?

 

[jwparker]

Its a basic metal enclosed air load break assembly. Current limiting or boric acid type fuse, or others depending on availability.

 

[Zogzog]

A 600E fuse is common for 5kV switches but not 15kV. Typically these are not sized for overload protection, just fault protection, your upstream brealers relays should be set for the OL. Hard for us to help without more info about your system.

 

[jwparker]

The fuse is for fault protection only. This is a primary feed from the utility for an underground 12kV distribution loop. The primary 12kV feed is supplied from the pole and into a 3 section load break assembly. The main section is fused while two secondary sections unfused to feed seperate 12-.6kV substions which are fully protected. Maybe the main fuse is unnessary as technically protection is being handled via cut-out on the pole however I would like there to be some protection there if possible. I dont see why a westinghouse RBA-800 with a 540E rating wouldnt work?


Utility
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Loadbreak/fuse
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Subsation#1 Substaion#2

 

[jghrist]

S&C offers 720A Type SM power fuses. See

http://www.sandc.com/products/smsml_id/smsml_ratings.asp

Also 600A Fault Fiter electronic power fuses. See

http://www.sandc.com/products/faultfiter/faultfiter_ratings.asp

You can't open the fuses under load, so you need a separate load-break switch.

 

[racobb]

Are you not satisfied with the utility fuse for fault protection? Sounds like for that level of load, the utility will already have something other than a fuse cutout on the pole. You may also have trouble coordinating a 500+ amp fuse with the utility protection.

If the utility has adequate fault protection why not just let them do the job. Then they are the ones buying those high dollar fuses. Hopefully you don't blow them often enough for it to be a problem anyway.

Alan

 

[davidbeach]

Why not protect each branch separately? Then you can use a smaller fuse and you will only loose one branch for a fault instead of both.

 

[jwparker]

davidbeach, Its a loop system so each branch needs to be able to handel the entire loop full current. The substations have primary fuses of their own.

Now considering removing the requirement for the fuse however I'm not sure of any code requirements for me to protect that conductor once it enters the building..?

 

[racobb]

Just picked up on the "metal enclosed" part once you said "it enters the building". Appears we were all thinking outdoor stuff previously.

Sounds from the voltage that you are in the US? Code may well require protection once it does enter the building.

Don't do the high voltage non utility stuff but other guys here do.

Alan

 

[jwparker]

Actually I'm in Canada. Its a 12.47kV system. If at all possible I will intend to keep the fuse in place. Any ideas would be helpful.

 

[racobb]

Then I expect Bill will offer some input!

Alan

 

[alehman]

Your options for fuses this size are limited.
What jghrist said. Parallel SM5's are feasible. You can only get the Fault-fiter in S&C switchgear (they don't sell it to other mfg's).

You might also consider vacuum fault interrupter gear such as Eaton MEP.

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[Elmir]

A 600A fuse at 12.47kV seems rather large.

The protection coordination should be reviewed as you may encounter problems coordinating with the local utilities upstream protection.

Where in Canada are you located?

 

[jwparker]

I've spoke with the utility and they are willing to install a non-fused 900A switch so coordination is not an issue. Fault protection will rely on our fuse. Would a 540E be more realistic?

 

[racobb]

Not much difference in a 540 or 600 amp fuse (60 amps). I guess if that's what it takes then so be it. I would still look at a three phase interrupter if the budget will stand it, especially if single phasing is an issue.

Alan

 

[jwparker]

I guess I suggested the 540E for availability. Some type of vaccume switch would be nice but pricey and complicated. We have sf6 switches for all the substations and I wanted to keep the main fuse simple.

 

[jghrist]

Alan brings up a good point. If your 12.5-0.6 kV substations have delta primary transformers and are fed by significant lengths of cable, you could have a serious ferroresonance problem when one fuse blows.

 

[jwparker]

They're wye primary. I guess I may consider going to a relay, Im worried about the cost.