# 3Ph 5KVA Transformer Troubleshooting with Anomolies



## jkcowboy (Aug 16, 2011)

All, I'm trying to figure out what happened with some transformers and hope someone has seen something similar before:

Problem: All three Xfmr (5KVA) Bank will blow a fuse when hooked up to 480VAC three phase. These are Acme 240/120 general purpose xfmrs. Primary: Ph1 to H1,H5 and Ph2 to H2,H6. Secondary: X1(Hot), X4(Neutral), X2/X3 connected. I haven't gotten far enough to see if this actually produced the desired Voltages or not. In the end, two of 6 windings primary windings are energized with full secondary.

Background: Transformer bank was built in Alaska years ago to step down 480VAC to two outputs: 380VAC Delta and 220VAC WYE to run some IEC Euro Equip. Rumor (no personal observation) has it that it ran good once. Not anymore. I think their thinking on how to transfer euro equip to run in the US is faulted, but I was paid to make the transformers produced the voltages at 60Hz. That part sounded easy to me.

I lifted leads on the primaries and secondaries and supplied 480VAC to input terminals, no xfmrs on line, to check the cord and input pwr fused switch, no problems. Meggared all three primaries and got a little less than an Ohm on each. Meggared the secondaries and got a little less than an ohm on each as well. Pri and Sec to ground was greater than 40 MOhm. Pri to the sec was greater than 40 MOhm. So far so good. I left the secondary leads lifted and one by one applied power to the primaries. No go. Each time the input Fuse (FRS-r-10A) blew immediately. All three transformers had the same readings, indications and all blew the fuse immediately. I just can't believe that 3 xfmrs would all go bad at the same time.

I'm going back tomorrow morning. My plan is to open the leads at the tranformer, pwr the primaries with a new wire straight from the generator and measure volt across the secondaries (x1 to x4). If it blows there... it has to be bad. Something just does not seem right to me.

What am I missing?

John King


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## brian john (Mar 11, 2007)

What size fuse?

What is the primary 480 to 240/120?


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## micromind (Aug 11, 2007)

If these transformers are 240 on one side and 120 on the other, they cannot be connected to a 480 system. 

If they are 480 (with taps) on one side and 120/240 on the other, I think (but am not sure) that the H side is not connected properly. 

I'll need more info; how many H leads are there? 

What is the nameplate voltage?

FRS fuses are time-delay, and will handle the normal inrush current of these transformers. 

The secondary is connected for 220 (or 240) wye.

If you connect any of the transformers directly to a power source without fuses, you'll almost certainly destroy the transformers. 


I somewhat suspect the transformers are dual primary, and connected for the lower voltage. The H1 & H5 and H2 & H6 is a parallel connection. For 480, you need series.


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## jhall.sparky (Jun 14, 2011)

jkcowboy said:


> All, I'm trying to figure out what happened with some transformers and hope someone has seen something similar before:
> 
> Problem: All three Xfmr (5KVA) Bank will blow a fuse when hooked up to 480VAC three phase. These are Acme 240/120 general purpose xfmrs. Primary: Ph1 to H1,H5 and Ph2 to H2,H6. Secondary: X1(Hot), X4(Neutral), X2/X3 connected. I haven't gotten far enough to see if this actually produced the desired Voltages or not. In the end, two of 6 windings primary windings are energized with full secondary.
> 
> ...


 
why?


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## brian john (Mar 11, 2007)

micromind said:


> If these transformers are 240 on one side and 120 on the other, they cannot be connected to a 480 system.
> 
> .


YES THEY CAN....Just not for very long.:blink: Hard to get that smoke back in those cases.


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## jkcowboy (Aug 16, 2011)

Couple of corrections. The xfmrs are 480/240 to 240/120 general purpose. I wasn't sure how they would be wired. I called Tempco and got a drawing showing how 480 could get to 380 but it was for a different series of xfmr. Yes, H1/H5 to H2/H6 are parallel connected. My output voltages are guestimates based on the label on the output switches and nothing else. I was hoping to take a read once the transformer was started. I have not been able to do that as of yet. Total of 8H leads. 4X Leads.

The output switches are identical and each has a neutral. They are using the 380 ph to ph and 228 ph to ground.

Any ideas why the xfmr would pop fuses after a good meggar. I always thought I would be able to find a short once suspected.

John


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## jkcowboy (Aug 16, 2011)

One more post asking why connect X2/X3? I don't know. Again, this is a weird voltage to achieve with this transformer set. I'm still figuring out what these guys did. I was hoping to see the output once the xfmr was started. Do you see any reason why connecting X2/X3 would cause a fault?


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## jhall.sparky (Jun 14, 2011)

jkcowboy said:


> One more post asking why connect X2/X3? I don't know. Again, this is a weird voltage to achieve with this transformer set. I'm still figuring out what these guys did. I was hoping to see the output once the xfmr was started. Do you see any reason why connecting X2/X3 would cause a fault?


 
other than a direct short ?...............

if it matters im still vague as to what it is they are trying to achieve......................


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## jhall.sparky (Jun 14, 2011)

jkcowboy said:


> All, I'm trying to figure out what happened with some transformers and hope someone has seen something similar before:
> 
> Problem: All three Xfmr (5KVA) Bank will blow a fuse when hooked up to 480VAC three phase. These are Acme 240/120 general purpose xfmrs. Primary: Ph1 to H1,H5 and Ph2 to H2,H6. Secondary: X1(Hot), X4(Neutral), X2/X3 connected. I haven't gotten far enough to see if this actually produced the desired Voltages or not. In the end, two of 6 windings primary windings are energized with full secondary.
> 
> ...


 
not being smart but these comments bug me and i think that the last comment is a whale shooting contest............ im not judging you im just not getting the WHAT THEY SAID part being relative, and im not gonna say that your wrong either just a few observations..............:thumbup:


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## frenchelectrican (Mar 15, 2007)

Jermey.,

The OP did update the information on the transfomer voltage connection however I do not know which way the OP did ran the transfomer in wye or delta primary side that is a sticky issue and I know normally you pretty much wired it up on delta on primary side however for the OP want to get to 380 volts to suit the European equiment and IMO the best aswer is either buck the transfomer with lowest setting if possible.

Otherwise a correct triphase transfomer with proper voltage connection slection.

380 volts will work with 400 to 415 volts due the V/HZ ratio is the same in both 50 HZ and 60 HZ 

But for the OP which way you ran the secondary side between the transfomers ?? that will make the differnce and poltary as well.

Merci,
Marc


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## jkcowboy (Aug 16, 2011)

Thanks guys and I can see quite a few interesting sides to this question, but for now I'm focusing on getting the transformers to run. The secondary was wired up wye with on lead to a common grounded wire and 3 hot legs... one from each transformer. 

But for now, I have every lead lifted and therefore the primary and secondary are not wire in any fashion. The transformers will not run. This is not an applications engineering problem yet. It is getting a transformer to run problem. If I could focus the discussion just on this and why my testing shows no faults, I would be most appreciative.


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## jhall.sparky (Jun 14, 2011)

jhall.sparky said:


> other than a direct short ?...............
> 
> if it matters im still vague as to what it is they are trying to achieve......................


 
marc,

thx im suspect to think we are right but..........................


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## micromind (Aug 11, 2007)

If the transformers are 240/480 to 120/240, and the primaries are connected H1&H5 to one incoming line, and H2&H6 to the other line, the reason the fuses blow is because this connection is for 240 volts, not 480.

The 480 connection would be incoming line 1 to H1. Incoming line 2 to H7 if it has 8 leads, H10 if it has 10 leads. On the 8 lead model, you'd connect H3 to H5, and isolate the other leads. On the 10 lead one, connect H4 to H7, and isolate the others. 

This applies only to Acme transformers that have all primary leads marked with an H. If there are some leads marked H and others marked with numbers only, the connections are different.

The reason X2 and X3 are connected is because X1 to X2 is a 120 volt winding. Same with X3 to X4. They are connected in series to yield 240 volts, then all 3 transformers secondaries are connected wye. The result, with the connections you've described and 240 input, is a 240/415 wye. This is a common European power connection. It's also known as 220/380.

If you're using a 480 input, you'll need to re-connect the primary as described above.


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## jhall.sparky (Jun 14, 2011)

micromind said:


> The reason X2 and X3 are connected is because X1 to X2 is a 120 volt winding. Same with X3 to X4. They are connected in series to yield 240 volts, then all 3 transformers secondaries are connected wye. The result, with the connections you've described and 240 input, is a 240/415 wye. This is a common European power connection. It's also known as 220/380.
> 
> If you're using a 480 input, you'll need to re-connect the primary as described above.


 
thxs i had it all twisted and wouldnt have thought it that way..............

just never seen one wired for this ....seems like there would be a dedicated 120 and 240 tap........... learned something today!......


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## jkcowboy (Aug 16, 2011)

Reporting success! Thank for all the comments. Here is what I did to fix the transformers:

1. I wanted a go-no go for each transformer. I jumpered a new line from the generator to a fused switch, 15A fuses were fine. Then I jumpered from the switch directly to the transformer. The existing Xfmr wiring had two of the six primary windings running in parallel. I rewired the Xfmr for standard 506 to 240 which uses the entire primary (H1 to H8) and entire secondary (X1 to X4). The secondary X1,X4 leads were lifted at the xfmr and left exposed for reading. It worked just fine. I scratched my head trying to figure what could be happening. What I think happened is someone rewired the primaries with parallel opposing fields which created an inductor vs a transformer with a primary current much higher than fuse settings.

2. I adjusted the primary L2 to connect to H7 vs H8 and the output was exactly 220V at 460 input. Good enough.

3. I then removed my jumpers one at a time converting back to using the installed wiring. All jumpers removed and the xfmr was still running good. The ONLY difference now was the way the xfmr was wired.

3. I repeated the procedure with the other 2 xfmr, rewiring each and lit off the bank. Good start, no noise, no blown fuses.

4. Final voltage at the output fused switch was 220V to ground, 380 V phase to phase. We hooked up the equipment and it ran like a champ.

In the end, someone must have messed with the wiring trying to fix or change something, of course no one fessing up. My test readings turned out to be correct, the xfmrs were good. Restoring the wiring to design returned the system to operation.

An open question to all, what exactly was happening to the two primary phases, obviously wired wrong, that would pop the fuses. Was I correct in my guess that they had created a big inductor? With open secondaries, the system was popping fuses. Based up this, with the infinite secondary impedance not being reflected to the primary makes me think we did not have a true transformer anymore. What do you think?

John King


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## micromind (Aug 11, 2007)

jkcowboy said:


> An open question to all, what exactly was happening to the two primary phases, obviously wired wrong, that would pop the fuses. Was I correct in my guess that they had created a big inductor? With open secondaries, the system was popping fuses. Based up this, with the infinite secondary impedance not being reflected to the primary makes me think we did not have a true transformer anymore. What do you think?
> 
> John King


As I have stated before (but obviously not written well enough to understand), the primaries were connected in parallel. This would be for a 220-240 volt source. When connected to a 480 volt source, the cores became immediately saturated, and the current went into the stratosphere. The fuses blowing saved the transformers from certain destruction.

You re-connected the primaries in series. This is for use with a 440-480 source. And the system worked as desired. 

The secondaries have always been connected correctly. 

Apparently, I need to take some writing classes or something; I'm just not getting through.


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## jkcowboy (Aug 16, 2011)

micromind said:


> As I have stated before (but obviously not written well enough to understand), Apparently, I need to take some writing classes or something; I'm just not getting through.


Micromind, thanks for the discussion of saturation in your last posting. That broke thru (where discussions on voltage did not) and got me thinking exactly what happens during saturation of a xfmr. As pri V keep going higher after saturation, flux does not and therefore the secondary loses (connection, control, effect on) the primary. As a voltage builds on the primary then here comes the current. If I'm close to being right now, it makes sense. I was stuck on the idea of one of the windings adversely effecting the other. I no longer think that is the case.

So no need for you to repeat yourself a third time. Who knows where my hard headedness and your sarcasm would lead.

John


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