How to Select Pole-Mounted Fuse?

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charlie b

charlie b

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On a US Military base, the service to a new building starts at fusible cutouts on top of a power pole. The government, not the utility, owns the pole and the overhead distribution system. The voltage is 13,800. The building's service transformer is 2000 KVA, with a secondary of 480/277V. Transformer primary and secondary protection is from fuses built into the transformer housing. Pole-mounted fuses would therefore only protect the primary conductors. They are 1/0, 15kV, MV-90, will be routed from the base of the pole to the building in underground ductbank, and have an ampacity of 200 amps. The contractor has asked me to select the type and rating of the fuses.

I am OK with using 200 amp fuses, but I don?t know one type from another. Anyone have a suggestion?
 
JoeStillman

JoeStillman

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Pick a fuse with a melting curve just to the right of the cable damage curve. They are allowed to be up to 300% of the ampacity of the 1/0's. (See 240.100). Current limiting fuses could help with available arc-fault energy available between the load side of the transformer and the 480V main - it depends on what you're trying to achieve.

Finally, it's important to coordinate the fuses with whatever is upstream on the 13.8 kV line.

200A looks about right without knowing what's upstream.
 
mbrooke

mbrooke

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charlie b said:
On a US Military base, the service to a new building starts at fusible cutouts on top of a power pole. The government, not the utility, owns the pole and the overhead distribution system. The voltage is 13,800. The building's service transformer is 2000 KVA, with a secondary of 480/277V. Transformer primary and secondary protection is from fuses built into the transformer housing. Pole-mounted fuses would therefore only protect the primary conductors. They are 1/0, 15kV, MV-90, will be routed from the base of the pole to the building in underground ductbank, and have an ampacity of 200 amps. The contractor has asked me to select the type and rating of the fuses.

I am OK with using 200 amp fuses, but I don?t know one type from another. Anyone have a suggestion?
Click to expand...

Well, a lot depends on that. Transformer inrush, coordination with other devices ect.


Assuming the pad mount will see minimal overload, lightning arrestors are before the pole cutouts, and all transformer protection is done with under oil bayonet fuses thus the cutouts only protect the cable something like a 100amp type T or a 140 amp type K fuse are usually what I would do.


However, this is only via rough details. In reality I would look at it in more detail. Other factors can change the size, speed and type of fuse. The time current curve of the transformer fuses if you wish to have a transformer fault clear its own fuse first need to be determined. The lateral protection to may need to be considered as well in case the protection is faster acting then the pole fuse for the cables.



Links are classified by amp rating and speed. The key is to get the right speed and amperage that gives enough overload capacity, lightning with stand where needed, selective coordination but still being able to clear a fault correctly.
 
JoeStillman

JoeStillman

Senior Member
Location
West Chester, PA
JoeStillman said:
Pick a fuse with a melting curve just to the right of the cable damage curve. They are allowed to be up to 300% of the ampacity of the 1/0's. (See 240.100). Current limiting fuses could help with available arc-fault energy available between the load side of the transformer and the 480V main - it depends on what you're trying to achieve.

Finally, it's important to coordinate the fuses with whatever is upstream on the 13.8 kV line.

200A looks about right without knowing what's upstream.
Click to expand...

I meant left . I always get them up mixed.
 
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