y to delta ...208v to 480v sec
- Thread starter blackburn
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Re: y to delta ...208v to 480v sec
Blackburn, you can do anything you need to do with it. Even though the input is 208 V, the neutral is not needed, so it is just a 208 3-phase delta input.
On the 480 V output you have several options, which one you chose depends on what it is going to be used for. For instance you could ground the Xo and make it a 480Y/277 system which would supply any 3-phase 480 V, and single phase 277 V loads. So what is going to be used for?
Blackburn, you can do anything you need to do with it. Even though the input is 208 V, the neutral is not needed, so it is just a 208 3-phase delta input.
On the 480 V output you have several options, which one you chose depends on what it is going to be used for. For instance you could ground the Xo and make it a 480Y/277 system which would supply any 3-phase 480 V, and single phase 277 V loads. So what is going to be used for?
roger willis
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Re: y to delta ...208v to 480v sec
Dereckbc, there isn't an XO on this side of the transformer he is using, only H1-H2-H3. He stated it was a delta so it can only be used for 480 volt 3 phase power. He can corner ground it if he wants to have a grounded system.
Just some thoughts.
Roger
Dereckbc, there isn't an XO on this side of the transformer he is using, only H1-H2-H3. He stated it was a delta so it can only be used for 480 volt 3 phase power. He can corner ground it if he wants to have a grounded system.
Just some thoughts.
Roger
roger willis
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Re: y to delta ...208v to 480v sec
Or, like Bennie said, there are transformers that you can buy for this purpose.
Roger
Or, like Bennie said, there are transformers that you can buy for this purpose.
Roger
roger willis
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Re: y to delta ...208v to 480v sec
Dereckbc, I understand, and I would agree with you in that case.
Roger
Dereckbc, I understand, and I would agree with you in that case.
Roger
Re: y to delta ...208v to 480v sec
If he does apply a 480v-208y/120v transformer as a step up, yes, the neutral of the 208y/120 system providing power to the transformer is not required but an EGC is of course, we all know that. But, don't overlook the fact that the XO is with almost all certainty bonded to the enclosure with a bonding strap of some type since the transformer secondary was intended to provide power as a separately derived system. I you don't remove that jumper that EGC will be connected to the XO and you will get current anflowing through the EGC.
As one of the other guys suggested corner ground the 480v delta as a grounded 'B'phase. Also, the HV taps work backwards since the transformer is being fed from the LV side. What would be commonly (2)+2 1/2%taps and (4)-2 1/2% taps now are just the opposite. Since it is not unusual for the supply voltage to be lower that that which is desired you will only have the ability to correct at either 2 1/2 or 5% where correcting for higher would be up to 10%.
Even though a 208-480y/277 transformer may be available standard design cost and stock availabiltiy may affect your choice.Don't forget to look at drive isolation transformers. The one that immediately comes to mind is a 208-460y/266.
If he does apply a 480v-208y/120v transformer as a step up, yes, the neutral of the 208y/120 system providing power to the transformer is not required but an EGC is of course, we all know that. But, don't overlook the fact that the XO is with almost all certainty bonded to the enclosure with a bonding strap of some type since the transformer secondary was intended to provide power as a separately derived system. I you don't remove that jumper that EGC will be connected to the XO and you will get current anflowing through the EGC.
As one of the other guys suggested corner ground the 480v delta as a grounded 'B'phase. Also, the HV taps work backwards since the transformer is being fed from the LV side. What would be commonly (2)+2 1/2%taps and (4)-2 1/2% taps now are just the opposite. Since it is not unusual for the supply voltage to be lower that that which is desired you will only have the ability to correct at either 2 1/2 or 5% where correcting for higher would be up to 10%.
Even though a 208-480y/277 transformer may be available standard design cost and stock availabiltiy may affect your choice.Don't forget to look at drive isolation transformers. The one that immediately comes to mind is a 208-460y/266.
roger willis
Member
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- Texas
Re: y to delta ...208v to 480v sec
The delta output of this type of connection is not required to be grounded, but may be grounded.
There are a lot of ungrounded three wire delta systems in large manufacturing plants. Systems of this type usually have ground indicator lights on them.
Roger
The delta output of this type of connection is not required to be grounded, but may be grounded.
There are a lot of ungrounded three wire delta systems in large manufacturing plants. Systems of this type usually have ground indicator lights on them.
Roger
Re: y to delta ...208v to 480v sec
As a former applications engineer supporting dry type distribution transformers using a transformer in either direction was a non issue as long as it was protected and wired correctly.
Also, with regard to using a ungrounded delta with ground indicating lights, this type of system is commonly used in factories where it would be very costly to shut down a part or all of a manufacturing process because of a ground fault. With an ungrounded delta there is no groundfault if one line goes to ground but is catastrophic when a second line goes to ground especially when it occurs in another part of the facility. Yes, ground fault indicating lights will indicate a grounded line but if the systems is not monitored by a qualified person who is familiar with the procedure to identify and isolate the grounded conductor, ground fault indicating lights are basically useless.
As a former applications engineer supporting dry type distribution transformers using a transformer in either direction was a non issue as long as it was protected and wired correctly.
Also, with regard to using a ungrounded delta with ground indicating lights, this type of system is commonly used in factories where it would be very costly to shut down a part or all of a manufacturing process because of a ground fault. With an ungrounded delta there is no groundfault if one line goes to ground but is catastrophic when a second line goes to ground especially when it occurs in another part of the facility. Yes, ground fault indicating lights will indicate a grounded line but if the systems is not monitored by a qualified person who is familiar with the procedure to identify and isolate the grounded conductor, ground fault indicating lights are basically useless.
Re: y to delta ...208v to 480v sec
I always get hammered on this subject but why not, here I go again.
No. 1. The transformer is being used for a purpose that is not intended. Tests would be made according to intended use. Not for reversal.
No. 2. The code states "when a transformer requires special connection procedure the information must be on the nameplate. The star point must float when the wye is the primary.
No. 3. A wye to ungrounded delta has no protection from winding to winding faults, even if the primary voltage is the lesser.
NO. 4. An ungrounded delta will have full voltage across the insulation on the first fault, making the second one more possible.
No. 5. The code requires all transformers to indicate the primary and secondary voltage on the nameplate. The nameplate will have only the high and low voltages. The catalog description will specify which is the intended primary and secondary.
I always get hammered on this subject but why not, here I go again.
No. 1. The transformer is being used for a purpose that is not intended. Tests would be made according to intended use. Not for reversal.
No. 2. The code states "when a transformer requires special connection procedure the information must be on the nameplate. The star point must float when the wye is the primary.
No. 3. A wye to ungrounded delta has no protection from winding to winding faults, even if the primary voltage is the lesser.
NO. 4. An ungrounded delta will have full voltage across the insulation on the first fault, making the second one more possible.
No. 5. The code requires all transformers to indicate the primary and secondary voltage on the nameplate. The nameplate will have only the high and low voltages. The catalog description will specify which is the intended primary and secondary.
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Re: y to delta ...208v to 480v sec
I'll say it again.
The present Square D transformer nameplates do not use the words primary or secondary, only high voltage and low voltage. -> No UL listing violation because high is high and low is low
Square D and GE wiring diagrams are shown with optional corner grounding on delta windings and an optional ground bond on the X0 terminal for wye connections. -> No UL listing violation because ground connections are optional and should be installed based on the requirements of the system.
Square D, Heavi-Duty, GE, and Hammond all have instructions for "reverse" connections in their published literature. -> No UL listing violation because the instructions show it as a valid use.
The only warning, I have ever seen, recommended against the use of "T" connected three phase units (common below 15KVA).
I'll say it again.
The present Square D transformer nameplates do not use the words primary or secondary, only high voltage and low voltage. -> No UL listing violation because high is high and low is low
Square D and GE wiring diagrams are shown with optional corner grounding on delta windings and an optional ground bond on the X0 terminal for wye connections. -> No UL listing violation because ground connections are optional and should be installed based on the requirements of the system.
Square D, Heavi-Duty, GE, and Hammond all have instructions for "reverse" connections in their published literature. -> No UL listing violation because the instructions show it as a valid use.
The only warning, I have ever seen, recommended against the use of "T" connected three phase units (common below 15KVA).
Re: y to delta ...208v to 480v sec
I have Catalog C-57, by the IEEE, ANSI, NEMA, and ASTM.
UL may list transformers, but the testing is performed by ASTM.
This publication contains the testing procedure and standards for all distribution, power, and regulating transformers.
There is no where, in the standards, a reference to reversing the input and output of any transformer.
The test procedure is based on the identification of the primary winding.
This concept, that a transformer can be reversed, was apparently started by someone who had just learned the transformer theory. Theoretically a transformer can be reversed. There is some, mostly single oil filled, that are reversible.
Common core winding transformers, are a different item, than single oil filled pots.
I have Catalog C-57, by the IEEE, ANSI, NEMA, and ASTM.
UL may list transformers, but the testing is performed by ASTM.
This publication contains the testing procedure and standards for all distribution, power, and regulating transformers.
There is no where, in the standards, a reference to reversing the input and output of any transformer.
The test procedure is based on the identification of the primary winding.
This concept, that a transformer can be reversed, was apparently started by someone who had just learned the transformer theory. Theoretically a transformer can be reversed. There is some, mostly single oil filled, that are reversible.
Common core winding transformers, are a different item, than single oil filled pots.
brian john
Senior Member
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- Leesburg, VA
Re: y to delta ...208v to 480v sec
Obviously this will work and IMHO grounded is always better that ungrounded in standard use (non industrial where shut down could cost a small fortune) The real problem would be with other electricians freaking from no voltage from one phase to ground and 480 VAC to ground on the other phases. I believe the best solution is to buy a 208delta to 480/277 wye.
Obviously this will work and IMHO grounded is always better that ungrounded in standard use (non industrial where shut down could cost a small fortune) The real problem would be with other electricians freaking from no voltage from one phase to ground and 480 VAC to ground on the other phases. I believe the best solution is to buy a 208delta to 480/277 wye.
Re: y to delta ...208v to 480v sec
I do not have the data any longer, but Bennie is correct. I did the research for a 1500 KVA, transformer. Not only is it a code problem it may be a Mfg. problem with some transfomers. The Mfg. would not warrenty the transformer used in this way. C-57 requires the H side to be conected to the primary. Talk to UL about this and see if you can get them to say in writing thats its approved.
The right answer is to get the proper stepup transformer.
If you look into it you will find that the Y to delta connection has its own set of problems and is seldom used because of these problems.
I do not have the data any longer, but Bennie is correct. I did the research for a 1500 KVA, transformer. Not only is it a code problem it may be a Mfg. problem with some transfomers. The Mfg. would not warrenty the transformer used in this way. C-57 requires the H side to be conected to the primary. Talk to UL about this and see if you can get them to say in writing thats its approved.
The right answer is to get the proper stepup transformer.
If you look into it you will find that the Y to delta connection has its own set of problems and is seldom used because of these problems.
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