Transformer Problem

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iwire

iwire

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I got an email from a friend, more of them are finding out I hang out here and would rather have me ask a question for them, shy I guess.

Here is the email.

I have two 225 kva 480 - 120/208 GE transformers at XXXXXX.

The first has a core temp of 140 c. Very lightly loaded.

Primary
"A" 9.3 amps 23.2 %Thd
"B" 7.29 amps 29.3 %Thd
"C" 11.9 amps 28 % Thd

Secondary
"A" 13.9 amps 6.4 %Thd
"B" 15.45 amps 18.2 % Thd
"C" 7.95 amps 10.9 % Thd

No neutral amps but 8.76 amps 7.4 % Thd on the grounding electrode conductor.

Does this prim to secd ratio cause the core to heat up more?

Or is my core bad?

This is a new K Rated trans.

The second trans is right next to it.
Core temp 108 c

Primary
"A" 23.46,
"B" 22.89,
"C" 20.01

Secondary
"A" 61.78,
"B" 86.6,
"C" 54.70.

This ratio seems more realistic for 480 - 120/208. No neutral amps but 7.4 amps to grounding electrode conductor.

What do you think or can one of your friends help.

This came up because the GE 400 amp breaker feeding trans would not hold.
Click to expand...
The no neutral amps but amps on the GEC make me think there is grounding bonding issues, but the breaker not holding I have no idea on. :confused:

Any ideas?, you have all the info I was given.

Thanks Bob

[ March 29, 2004, 07:35 PM: Message edited by: iwire ]
 
Re: Transformer Problem

No neutral current? :eek: :eek: Sounds like the place to start too me. My guess it is completely wired incorrectly.
 
Re: Transformer Problem

The loading does not compute. No neutral current means open neutral.

Look for a layer to layer, winding to ground, or high to low fault.
 
Re: Transformer Problem

"Sound's like one of the voltage tap windings on the secondary is reversed polarity"


Wayne, I feel kind of dumb, but I do not understand what you mean, I am sure that is my lack of transformer knowledge, not your post.

Can you elaborate?

Thanks, Bob
 
Re: Transformer Problem

Let?s make sure we are using our terms in the same way. When you say ?grounding electrode conductor,? I think you mean the wire that connects to the center point of the WYE on the secondary side, and goes to planet Earth via a ground rod. That wire should not have any current. Are you certain that that is the wire on which you are measuring the current values of 8.76 amps (first transformer) and 7.4 amps (second transformer)? If it is, then you have a ?fault.? This term could mean a wiring error (most likely), an open neutral (also likely), or a manufacturing error (less likely).
 
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