Medium Voltage Cable

[Shujinko]

There is an existing installation that I am about to start working on where the owner sent me a picture of the inside of a step up transformer 480Y/277V (Pri) to 12470Y/7200V (Sec). The picture is not clear but the Medium Voltage side of the transformer does not appear to have MV cable installed. What is the consequence of using 600V rated conductors on an MV system? Does the NEC or IEEE define the color scheme for medium voltage system cables? I thought brown, orange, yellow was the conductor colors required for a 480Y/277V system. See attached pic of the 12470Y/7200V terminals of the existing transformer.

 

[SG-1]

The consequence would be Catastrophic Failure.

Lets hope this is the 480/277 side.

 

[electrofelon]

There is an existing installation that I am about to start working on where the owner sent me a picture of the inside of a step up transformer 480Y/277V (Pri) to 12470Y/7200V (Sec). The picture is not clear but the Medium Voltage side of the transformer does not appear to have MV cable installed. What is the consequence of using 600V rated conductors on an MV system? Does the NEC or IEEE define the color scheme for medium voltage system cables? I thought brown, orange, yellow was the conductor colors required for a 480Y/277V system. See attached pic of the 12470Y/7200V terminals of the existing transformer.


View attachment 20295

The picture is of the low voltage side not the HV side.

 

[zbang]

I thought brown, orange, yellow was the conductor colors required for a 480Y/277V system.]

It may be required by the building or site's practice, but not by the NEC.

 

[Tony S]

Not that it helps, I tested a piece of 1000/600V T&E (similar to romex) to 16kV before the insulation broke down.

 

[Sahib]

Because voltage breakdown follows statistical rule, do not expect immediate breakdown on application of high voltage. For example, here in substandard installation of neon sign boards, ordinary LV cables connect to neon tubes and the neon board continues to glow for some time.

 

[Besoeker]

Not that it helps, I tested a piece of 1000/600V T&E (similar to romex) to 16kV before the insulation broke down.

I've done that sort of thing too. Time.....

 

[jim dungar]

step up transformer 480Y/277V (Pri) to 12470Y/7200V (Sec).

Like electrofelon said, this is the low voltage compartment.

According to standard conventions, like ANSI/IEEE, the H and X terminals do not signify primary and secondary but rather high and low voltage. You need to look at the the transformer nameplate.

And yes, I realize some step-up transformers do not follow this convention.

 

[kingpb]

The connections to the bushings look dramatic; why would you bolt terminal block to the bushing, instead of simply applying a one or two hole compression lug to the cable. This looks like a do-it-yourself setup.

 

[Shujinko]

Like electrofelon said, this is the low voltage compartment.

According to standard conventions, like ANSI/IEEE, the H and X terminals do not signify primary and secondary but rather high and low voltage. You need to look at the the transformer nameplate.

And yes, I realize some step-up transformers do not follow this convention.

See attached pics of the transformer nameplate and primary side compartment (LV side). On the primary side of the transformer there is an existing 1500KW 480Y/277V diesel engine generator. On the secondary side of the transformer there is a 12470Y/7200V MV utility switch. If you look close at the original pic in my post, there seems to be evidence of arcing on lugs and there also seems to be one set of conductors missing on the neutral lug. There are 2 sets of conductors on all phases and only 1 set of conductors on the neutral lug. It seems that I should recommend that the secondary side (MV side) of the transformer needs to be upgraded to MV cable and correct conductors, as far as # of sets and conductor sizes. What do you think? What should I tell my client which has limited funds?

 

[Shujinko]

The connections to the bushings look dramatic; why would you bolt terminal block to the bushing, instead of simply applying a one or two hole compression lug to the cable. This looks like a do-it-yourself setup.

You may be correct on this one. Maybe the installer didn't do the best job on this.

 

[zog]

Again, your photo shows the LV side, see that sticker that says "HV behind barrier"?

 

[Shujinko]

The consequence would be Catastrophic Failure.

Lets hope this is the 480/277 side.

Nope, this is the MV side. The 480Y/277V side has a 1500KW generator upstream of it so the terminal lugs have alot more conductors installed on it. Have you ever seen MV cable color coded Brown, Orange, Yellow?

 

[electrofelon]

So you have shown us two picures of two different transformers, both pictures of the right hand, low voltage side. I'm not really clear on what the question is.

 

[Shujinko]

So you have shown us two picures of two different transformers, both pictures of the right hand, low voltage side. I'm not really clear on what the question is.

Yes you are correct, I see the mistake now. The client sent me some tight photo shots of the transformer without any wide shots and I haven't gone to the site myself to confirm. I will get more photos in the next couple of days when I visit the site and re-post and confirm if there is a MV cable issue as noted in my original post. Thanks and I apologize for the confusion.