Padmount Transformer Fusing

[DetroitEE]

I have a situation where we will have a fused 15kV primary switch ahead of a pad-mount transformer. I have specified expulsion type fuses in the primary switch. I am unclear what type of fusing should be provided in the transformer. It seems to me you would still want some internal fusing to protect the secondary and to protect the transformer from internal faults. I found a pretty good paper which clearly describes the different types of transformer fuses available. www.aedie.org/9CHLIE-paper-send/218-ZAMORA.pdf

Does anyone have any experience with this type of setup?

 

[jim dungar]

... some internal fusing to protect the secondary and to protect the transformer from internal faults....

You cannot protect the transformer from internal faults. The fuses are there to protect the power grid from a faulted transformer. In your case the internal fuses would be redundant to the external fuses.

 

[DetroitEE]

You cannot protect the transformer from internal faults. The fuses are there to protect the power grid from a faulted transformer. In your case the internal fuses would be redundant to the external fuses.

Thanks for the input Jim. I notice that a standard option for pad mounts is to have a back-up current limiting fuse. Per an IEEE 007 paper that I found, this is to limit the energy delivered to a fault in the core. I'm thinking that it might be a good idea to incorporate a liquid immersed current limiting fuse in the transformer as the "backup", with the expulsion fuse in the primary switch acting as the main OCPD.

 

[jim dungar]

Many, if not most, padmount transformers are tapped off of common feeders, so it is good for them to have their own internal protection. In your case you have a dedicated external feeder which can provide the same functions.

If your installation was not padmount construction, would you still be trying to figure a way to have internal fusing?

 

[DetroitEE]

Many, if not most, padmount transformers are tapped off of common feeders, so it is good for them to have their own internal protection. In your case you have a dedicated external feeder which can provide the same functions.

If your installation was not padmount construction, would you still be trying to figure a way to have internal fusing?

Valid point, I may be overthinking it.

 

[T.M.Haja Sahib]

Valid point, I may be overthinking it.

May not be. A current limiting fuse is better than an expulsion fuse in preventing transformer explosions due to heavy internal arcing fault.

 

[Hv&Lv]

We use Bay-o-Net fusing in all our PMT's. Generally the ones that come with the unit when purchased. I agree with Jim that it is redundant. When you think about it, the fuses are at each end of the primary wire only. One at the top of the pole, the other happens to be just inside the PMT... It is good at protecting the wire when arrestors and fuses are at each end though.

 

[DetroitEE]

The primary fuse is a medium voltage expulsion type power fuse, similar to this one http://www.cooperindustries.com/con...wer_fuses/clip_mount_fuses/cmu.resources.html .

After reading the documentation for this product, it makes it sounds like additional protection would not be required if I have this in a medium voltage switch on the primary side of the transformer.

 

[jim dungar]

We use Bay-o-Net fusing in all our PMT's.

Yeah, but equipment cost doesn't mean anything to a utility.