Have a Federal Pacific TX40T51-A 208x240x480 pri, 400Y/231 sec 51KVA, using 240vac pri, and 400 sec Y config. When you throw the disconnect mounted on the side of transformer it will blow the breaker on the primary. We even hooked the primary direct to a fused disconnect feed with 125 slow blows in it and it knocked out our 200 amp main breaker. This transformer is drawing like up to 9 amps no load also. Odd thing is I have another FP trans that is 75 KVA setting right beside it and it never has blown anything and the highest leg draws a mere 3 amps. Fed Pacific claims nothing wrong I am mystified how one does this and the other one does not.
3PH transformer blows breaker on power up
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MTW
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Post the tag from the transformer, it appears as a non standard unit, used in reverse.
petersonra
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I suspect there is some kind of problem that should be looked at by a qualified person. I don't see anyway to debug your problem from the Internet. Is the 9 Amps on the secondary or primary side? Is this a new install or has it been working and just started this behaviour?
It is also possible the transformer is fine and the CB is just tripping from startup inrush current. Does it happen every time you power up the transformer?
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New install, new transformer, 9 amps on primary side amp load varies per leg with machines disconnect turned off of course. It will blow the breaker several times and finally it holds.
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What size is the OCPD on the primary?
Tulsa Electrician
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Is this a true step up transformer
125amps
yes it is
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Keep trying now that you have a few posts you may be able to shortly
petersonra
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the OP indicated it was blowing their 200 A main breaker.
petersonra
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I don't think this is the nameplate on the transformer.
petersonra
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if you copy the picture to your clipboard, you may be able to just past it in your reply.
petersonra
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- Northern illinois
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- engineer
51 KVA at 240 VAC 3 phase is about 120 Amps. A 125 Amp CB seems kind of small to me. I would normally use about a 200-250% breaker.
That is correct when we un-hooked the primary from the breaker and put it over on a fused disconnect with slow blows in it, didnt take out the slows blows but blew the main 200 amp disconnect breaker on outside of building that directly feeds that disconnect with slow blows.
I understand the inrush deal but taking out a 200 amp breaker???? And I have a 75kVA same model setting next to it being feed from another 200amp feed and it never blows the 200 amp feed breaker.
petersonra
Senior Member
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- Northern illinois
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- engineer
the larger xfmr may have a higher impedance leading to less no load current. or there may be something else going on. it is very hard to debug this kind of problem without being there.
have you checked the voltages? is whomever is doing the current measurement using a true rms meter?
does either breaker have an adjustable IT setting?
MTW
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Your existing 75 KVA unit may be older and less efficient model that has a lower inrush current.
Newer mandated high efficiency units have a much higher inrush current, as do motors. Fuses can have better holding capabilities on inrush. Breaker is tripping faster, with instentaneous magnetic current.
Newer mandated high efficiency units have a much higher inrush current, as do motors. Fuses can have better holding capabilities on inrush. Breaker is tripping faster, with instentaneous magnetic current.
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