Transformer Loading

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gee111

Member
I have a concern that I happened to run across today and I am hoping that someone out there can shed some light on it for me. I am currently managing a project for the USAF here in San Antonio and I ran across something of concern today in reference to one of the Dry-Type Transformers installed at this particular project area. While walking by the XFMR, I noticed a very loud humming noise coming from the unit. I walked over and did a quick visual on it and could actually feel the heat eminating from the unit at a distance of 5 feet. I had one of the on-site technicians shut down the control (circuit breaker) and tag the unit out of service for further inspection. The case of the XFMR was too hot to touch without gloves on when we removed the front panel. I did not notice anything out of the ordinary nor did I discover any physical damage. One thing that I did notice is that the load on the XFMR was almost nil. The XFMR is a step down....480/277 to 208/120 150 kVa and is currently powering a 3 phase 120/208 400 Amp panelboard which only has a load of about 1 amp total on it!!! Is the lack of load on the transformer the problem?
 

bphgravity

Senior Member
Location
Florida
Re: Transformer Loading

Transformers are not exactly like motors, underloading them should not be an issue. Is there a possibility that you have nonlinear or harmonic loads on the secondary?
 

gee111

Member
Re: Transformer Loading

None that I know of that are of any consequence. The only load on the whole system is 2 32 watt fluorescent light fixtures.
 

hurk27

Senior Member
Re: Transformer Loading

You could have a winding fault just a couple turns in from the X0 tap which would cause it to produce allot of heat. Check the current on the primary if the fault is there so will the primary current reading. If you have phantom current on the primary then further checking has to be preformed. after removing power unhook the XO bond and open any load side disconnects and or other bonds then check case to XO to see if you have continuity.

If you do well it's replacement time. :D
 

gee111

Member
Re: Transformer Loading

I was actually thinking of the very same thing right before you posted. I wanted to exhaust my resources though since this XFMR is brand new but I guess it is possible to have a new faulty piece of equipment. Any other possibilities that you can think of just in case?
 

hurk27

Senior Member
Re: Transformer Loading

Yep taps not correctly connected to the right terminals. reversed mid phase connection of a winding, had that happen once when the factory miss marked the wires. But in any case primary current should reflect the load on the secondary. This will be the first clue to something being wrong.
 

hurk27

Senior Member
Re: Transformer Loading

And just in case the current does pan out corectly then look for air flow problems around the transformer that would cause it to have a higher rise then it should.
 

gee111

Member
Re: Transformer Loading

Sounds like a good starting point and I appreciate the help. This was my first time on the forum and I think I will be a permanent fixture here from now on!! Ha Ha! Thanks again.........James
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Re: Transformer Loading

Originally posted by gee111:Any other possibilities that you can think of just in case?
Loose connection? :confused:

If it's "brand new," was any testing performed after its installation? If so, can you get the records? If not, perhaps "hurk27" is right, that you got a bad unit and it needs to be replaced.

Charlie B. (Born & raised in San Antonio)
 
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