Transformer question.

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esox39

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I have a 120/240 three phase delta service. I need to step this up to 277/480 3 wire. The transformer I got has the markings. X1,X2,X3,X4 and H1,H2,H3. I connected the 120/240 A Phase(120V) to X1, B Phase(200+V) to X2 and C Phase(120V) to X3. What is X4 used for? I never ran accross this. Any help would be appreciated.
 
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Is there a nameplate on the transformer? If there is: Is there a model number, or any other data on the nameplate.

With no more than what information you have given, I'd say the 240D side is H1, H2, H3. X1, X2, X3, X4 is the 480V secondary side.

You would never connect the neutral on the primary side. You really need the nameplate data.

(edited to add x1... 480V information)

cf
 
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Without the nameplate data that Mr. Fusion is asking for, we are just guessing here.

Given that you've connected your 240V supply to the 'X' terminals, my guess is that you have the wrong transformer for the job. It sounds like you have a 480V delta to 240V delta step down transformer, and that the X4 terminal is the center tap on one of the coils. If this is the case, then you connect nothing to the X4 terminal, and your output will be a 480V _delta_, not your desired 480/277V.

The transformer that you really want for this job has a 240V delta and a 480V wye step up transformer. It will have _3_ terminals on the 240V side, and _4_ terminals on the 480V side.

-Jon
 
Sounds like you're using a typical step down transformer in reverse. So instead of Delta/Wye you now have Wye/Delta which will not give you the desired 480Y/277 volt output on the secondary side.
 
The ANSI standard for transformers says that H terminals should be the high voltage and the X terminals the low voltage regardless of step down or step up. However industry practice is to call the H terminals the primary and X the secondary.

I agree it sounds like the OP's transformer has a 480V 3-wire delta high voltage connection and a 240/120V delta low voltage connection. This transformer should not have the X4 terminal connected when used as a step up unit. As a step-up unit it will not provide a 480Y/277 output.
 
infinity said:
Sounds like you're using a typical step down transformer in reverse. So instead of Delta/Wye you now have Wye/Delta which will not give you the desired 480Y/277 volt output on the secondary side.
Click to expand...

As I alluded to earlier, that's one possibility. However, building on Brian's idea, 240/120 (4wire) primary/240/120 (3wire) sec, single phase sounds better.

cf
 
sandsnow said:
John is correct about what type XFMR you need. A 240 delta to 480Y/277 should have an H4 not an X4
Click to expand...
If it's configured for wye-type 3? 4W input or output, there would be no H4 or X4 terminal. Wye configuration uses a H0 or X0 terminal as marking for the neutral.
 
The is the way I would consider it:
Judging from the minimum of information provided you have a 480V delta-240v delta/120 step down transformer. I will be marked with H1, H2 and H3 for the 480v connections and the secondary is a 240v delta with a center tap on one side of the delta. It will be marked with X1, X2, X3, and X4. The X1, X2, and X3 form the delta and the X4 is a center tap between the X1 and X2.
This transformer could be used to step up a 240v L-L-L source by connecting it to X1, X2, and X3 with no connections required to the X4. The 240v is then stepped up to 480v at H1, H2, and H3.
Remember that you have (3) issues though:
!) This is a 480v delta where there is no neutral point and as such a 480Y/277 is not possible.
2) The only means of grounding a 480v delta is to corner ground it. Any ground fault will be 480v to ground.
3) One would expect the inrush current that is requited to magnetize the core to be proportionate, Whether the transformer is feed from the HV or LV side but it isn't.
In a step down transformer the HV coil is wound on the outside of the LV coil and away from the core itself. Remember that the taps are located on the outside HV coil with the LV coil next to the core the inrush is much greater. If the inrush is 10x the transformers HV rated current when energizing a step down transformer the inrush will be greater than 10x the transformers LV current rating should the transformer be applied as a step up which can be quite a challenge when applying an OCPD.
A LV (600v) transformer that is properly designed as a step up transformer will have the LV coil wound on the outside of the HV coil and the taps located there. Since the LV coil is farther away from the core, the magnetizing current inrush will also be less. Also, a good transformer design will also add more iron to the core to reduce flux density will also reduced inrush.
Steps up transformers are somewhat more expensive to build that their step down counterparts.
 
I connected the transforer like I thought it should be done. X1, X2 and X3 to the 120/240 delta. This is being used in a step up configuration. On the H1, H2 and H3 connections I got the 480V I was looking for. I did not use the X4 connection because I was looking for power only. I had just never seen the X4 terminal. I have seen XO but not X4 and that is what confused me. Thank you all for all your help as always.
Ron
 
esox39 said:
I connected the transforer like I thought it should be done. X1, X2 and X3 to the 120/240 delta. This is being used in a step up configuration. On the H1, H2 and H3 connections I got the 480V I was looking for. I did not use the X4 connection because I was looking for power only. I had just never seen the X4 terminal. I have seen XO but not X4 and that is what confused me. Thank you all for all your help as always.
Ron
Click to expand...

What no part number, no picture ? :cool: Come on you can tell us we are your friends, you used a step up xfmer and back fed it didn't you ? :wink:
 
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