Transformer Hot, 3 phase supplying a 1 phase panel

[brother]

There has'nt been an infared done on this transformer, but first glance to me it seems a little unusually hot. Too hot to leave your hand on. It's an old install.

What I did notice it was a 3 phase transformer, 15kva, 480 primary to 208/120 secondary. The transformer is fed froma 3 phase panel. The panel it feeds aparently is only a 3 wire, single phase, 120/208. It's only using 2 of the phases of the 3 phase transformer secondary. Could this 'imbalance' cause the extra heating.???? I do not know why they installed this way, or why they just didnt use a 3 phase panel.

Maybe this is normal heat, but its the first Ive seen(felt) this hot in a while.

 

[e57]

Hot hot is hot? And how hot is too much?

 

[brother]

Hot hot is hot? And how hot is too much?

Thats goes back to the infrared reading we will have to take.

 

[cadpoint]

No Amperage reading done ?

 

[iwire]

Is it an encapsulated transformer?

What are the temp ratings on the tag?

 

[jim dungar]

Even a "low temperature rise" transformer can have surface temperatures which are too hot to touch.

 

[drbond24]

I don't see how the install you describe would cause any undue amount of heat.

It could be quite hot to the touch and still be OK. If you get 3rd degree burns from leaning on it, then it's a problem.

 

[nakulak]

what color orange is it ?

(dried cut on my hand red, fresh cut on my hand red, traffic cone orange, sunny-D)

if its any color but transformer green, its probably too hot.

 

[augie47]

I "played" with numbers in reference to this post and confused myself (eassy task).
If we have a 15kva 3 phase 208 transformer out outpurt current should be
15000/208 x 1.732 or 41.6 amps thus calling for a 52 amp secondary OCP
(upped to 60).
If we feed a single phase panel, our usable output on a 3 phase 15kva transformer would be 10 kw or 10000/208= 48 amps still a 60 amp OCP.

But is my math correct as far as the outputs ?

 

[sameguy]

reduce out put by 10% when 3phase pri. and 1phase sec.

 

[hardworkingstiff]

I "played" with numbers in reference to this post and confused myself (eassy task).
If we have a 15kva 3 phase 208 transformer out outpurt current should be
15000/208 x 1.732 or 41.6 amps thus calling for a 52 amp secondary OCP
(upped to 60).
If we feed a single phase panel, our usable output on a 3 phase 15kva transformer would be 10 kw or 10000/208= 48 amps still a 60 amp OCP.

But is my math correct as far as the outputs ?

Another way to look at it is:

41.6A * 208V = 8.65KVA
or
41.6A * 2 *120V = 9.98KVA (or 1.15 x the 208V calculated connection)

1.15, hummm, isn't that the number in the discussion of the Oregan Fudge Factor?

EDIT: Just for the record, I hate serving a single-phase panel with 2 phases of a 208Y/120V transformer.

 

[hurk27]

EDIT: Just for the record, I hate serving a single-phase panel with 2 phases of a 208Y/120V transformer.

yep because the neutral will always be a current carrying conductor in the wire counts:roll:

 

[hardworkingstiff]

yep because the neutral will always be a current carrying conductor in the wire counts:roll:

That is a reason, but the biggest one for me is I hate serving 240V equipment with 208V. Yea yea, I know, get the HO to buy 208V rated equipment. Well, they shouldn't have to do that, my opinion, and it's staying that way.

 

[brother]

I "played" with numbers in reference to this post and confused myself (eassy task).
If we have a 15kva 3 phase 208 transformer out outpurt current should be
15000/208 x 1.732 or 41.6 amps thus calling for a 52 amp secondary OCP
(upped to 60).
If we feed a single phase panel, our usable output on a 3 phase 15kva transformer would be 10 kw or 10000/208= 48 amps still a 60 amp OCP.

But is my math correct as far as the outputs ?

how you get 10kw for the secondary out put??

 

[aelectricalman]

Just balance the load out as much as possible and whatever you do dont cool it down with water!

 

[ceb58]

Can be a good place to warm your lunch

 

[aelectricalman]

Can you explain that augie? It seems like the output should still be based off of 15KVA

 

[Cold Fusion]

Can you explain that augie? It seems like the output should still be based off of 15KVA

Isn't the transformer kva based on heat rejection? I'm thinking that each coil is by it's self. So you would be looking at 3 - 120V coils at 5kva each.

2 X 120 X 41.6 = 9.984kva.

cf

 

[hurk27]

Can you explain that augie? It seems like the output should still be based off of 15KVA

simple 15/3=5*2=10kva

you are using 2/3's of the transformer, there are other ways to calculate it but thats the simple one I know.

 

[augie47]

how you get 10kw for the secondary out put??

I stand to be corrected, but I was taught a 15 kva 3 phase transformer was like having (3) 5 kw coils..if your load is only single phase, then you only have 10 kva capacity