General question about customer owned transformer HV protection 1

[bdn2004]

We have a small project to perform a power study for a new waste water facility. In the project documents they are specifying a new 750 kVA, 12.47-480V pad mounted, oil filled transformer. But they are NOT specifying new fuses in the HV terminal cabinet of that transformer. Is this the standard way this is done - rely on the Utility to provide the fuses for a transformer you own?

The construction is....a 12.47kV tap off the Utility pole line assuming Utility furnished cutouts on the pole, underground 50'+ 12.47kV cable -> 750kVA transformer -> 150' secondary conductors landing at a remote main circuit breaker inside the building.
(This seems odd too - is there not a tap violation here ? )

 

[SwinnyGG]

Based on the configuration you've just described, I would expect that the owner of the facility does not own that transformer.

 

[bdn2004]

It's a new installation that has not been put in yet. It's a requirement per the Contractor's job specifications that they get the power study done PRIOR to installing it - which is good. They got quotes from a Vendor (Square D) of the equipment they are providing - and that 750 kVA transformer is part of it. Also it's showing primary metering - which is the point of demarcation between you and the Utility.

 

[SwinnyGG]

Interesting.

Our utility would never do it that way... but that's our utility.

If it's primary metered, the question on who provides fuses can probably only be answered by the utility, or the contractor. I can see a scenario where they don't plan to provide them because they know how the utility operates and that the utility wants to provide them.

I can also see a scenario where it's just an error on the part of the contractor.

If your contract for this power study stipulates that you have to solve any issues with their scope of supply, it sounds like you have an RFI to write. If it doesn't, it sounds like a courtesy email to the contractor and then getting on down the road.

 

[bdn2004]

It's a somewhat generic specification for the power study. And there's nothing in our scope about doing any design - that's supposedly already done. I'll send them an email for clarification. Thanks.

I just wondered if this is a typical way this is done? Got you down as a No vote. Our office building is kinda like this same installation... pad mount right outside the building, doesn't look like there a fuses installed there - but the Utility owns that transformer. That makes sense to me.

 

[nhcf]

In the one primary metered configuration that I did a preliminary design for - I included gang-operated switch w/cutouts at the service point to comply with 230.205. The contractor disagreed that it was needed since most secondary metered services do not have that. Someone else ended up doing the detailed design, and i don't think any separate fuses or switch were included.

 

[stevenal]

Padmounts would typically have bayonet style fuses under oil. Nothing to see without opening the high voltage compartment door (trespassing if utility owned).

 

[bdn2004]

https://www.hagerstowncc.edu/sites/default/files/2022-04/Square D Class 7230 Manual.pdf

This is the transformer that is specified: Square D 7230. But it specifically says there is no fusing in the quote - and it looks like in the literature they are optional.

 

[SwinnyGG]

I just wondered if this is a typical way this is done? Got you down as a No vote

Eh... it's certainly not typical for my utility.. but in my experience different utilities can have vastly different policies on who provides what and who pays for it.

 

[dpc]

Even if you are taking service at medium-voltage, it's still a service and the transformer requires protection and there must be a disconnecting means (not owned by the utility) to meet the NEC, in my opinion. Pad-mounted transformers can have oil switches and most have bayonet fuses under the oil. Load break elbows can be fused as well. I wouldn't want to rely on the utility to protect a transformer I owned. They have a completely different mindset toward protection of their distribution transformers.

 

[jghrist]

It may be possible for the utility cutout fuses to act as the service disconnect, if the service point is defined ahead of the cutouts. The utility normally defines where the service point is. If the service point is ahead of the cutouts, you will need to have a gang-operated switch as well as the cutouts.

More than likely, however, the utility will define the service point to be at the transformer, in which case, you will need to have a gang-operated disconnect and short-circuit protection at the transformer. If there is no switch and fuses furnished with the transformer, you will need to have a separate switch and fuses ahead of the transformer. It would be a lot easier, if transformer is not already purchased, to specify a switch and fuses in the transformer. Also, specify a locking means so that you can do proper lockout/tagout.

 

[bacon4life]

Another vote here that omitting the bayonet fuse would be unusual. In my area utility the fuses would be sized only for the protection of the primary cable, meaning the fuses would be totally inadequate for protecting the transformer.