PadMountedDistributionTransformer

[Engcan]

Happy New year 2006 to all the members, who read and reply.

Here is my question. I know the answer but just want to make sure if I am right.

In case of a single phase pad mounted distribution transformer, there are three fuses. I want to make sure what I know, is it correct?

The first fuse is the expulsion fuse and lighting arrester combination at the riser point on overhead line. then comes the transformer. There could be two possibilities
for transformer
1. Current limiting fuse+ Bay-o-net fuse + Isolation LInk
2. Bay-o-net fuse + isolation link.

which of the two option is correct and if yes which is one used. I am just confused about this combination and
if option 1 is correct, is it true that the expulsion fuse at riser point is supposed to blow first then curent limiting fuse ?

Note: Do we have to give the TCC of expulsion fuse to manufacturer so that he coordinates bay-0-net with explusion?

Best Regards,

 

[wareagle]

It depends on the type of pad mt. You can get one that only requires the riser fuse and it is rated for the transformer size. You won't need the others.

 

[jtkirb]

The riser fuse is protecting the feeder to the xfmr. The bay-o-nets are protecting the transformer.

You need to make sure the Xfmr fuses lay under the riser fuses on the TCC curves. A transformer fault will clear the bayonets and a cable fault will clear the riser fuses.

JTK

 

[wareagle]

jtkirb posted "The riser fuse is protecting the feeder to the xfmr. The bay-o-nets are protecting the transformer."

If this was a primary loop to several transformers I would agree. The post says "In case of a single phase pad mounted distribution transformer, there are three fuses."
The riser fuses can be sized for the transformer capacity.
Example: 7.2 kv 75kva 240 volts has a primary load of 10.4 amps. The riser fuse can be a 15 amps fuse with cable being #2 AL URD good for over 100 amps. No need for any other fuses. The secondary must be protected per NEC requirements.

 

[jtkirb]

I assumed that he already had bay-o-nets in the transformer (is this the case?). You still need cable protection, so make sure you size the riser fuses so you have good coordination.

You are correct in that you could order the transformer without the fusing and use the riser fuses for total protection.

JTK

 

[dpc]

If this is a single dip to one transformer, the coordination between the cutouts at the dip pole and the transformer bay-o-nets is not crucial. The outage would be the same. If the dip fuses are feeding several transformers, then I agree that coordination is "a good thing".