Xformer delta-delta with high leg situation, (irregular voltage)

[LarryFine]

Normally, primary taps are used to compensate for non-nominal supply voltages. The desired/required secondary output voltage, and thus the volts:turns ratio, are known values. We adjust those taps to set those known values where we want them.

 

[jim dungar]

In getting 501v on 2 of 3 phases and 480 on the third

I assume you mean you are getting 501V between two sets of two Line conductors say A-B and B-C and 480V between one set say C-A.

 

[Burdaneta]

I assume you mean you are getting 501V between two sets of two Line conductors say A-B and B-C and 480V between one set say C-A.

Correct

 

[Elect117]

I think when you had the low side split phase grounded there was some leakage and since the high side is ungrounded (nor bonded) it is floating at a non zero point. Similar to a momentary GF where the neutral point has been shifted.

And just out of curiosity, these values did not change when you turned the xfmr off and back on?

 

[don_resqcapt19]

No, he has a 240v high-leg delta. He keeps bringing up the 208v high leg.

Post 1 says otherwise "a new xformer step-up to convert our 120/208v service to 480v"

 

[LarryFine]

Post 1 says otherwise "a new xformer step-up to convert our 120/208v service to 480v"

Subsequent posts suggest he was improperly using the L-N voltages of 120 and 208 for the designation.

 

[Burdaneta]

Normally, primary taps are used to compensate for non-nominal supply voltages. The desired/required secondary output voltage, and thus the volts:turns ratio, are known values. We adjust those taps to set those known values where we want them.

Taps moved to number 5 , output voltage A(480), B(479), C(473) , work just great thanks for all your help guys, now we ready to use it.

 

[winnie]

Taps moved to number 5 , output voltage A(480), B(479), C(473) , work just great thanks for all your help guys, now we ready to use it.

Glad you have the voltages correct.

You are still going to need to deal with the issue of grounding your 480V system.

You said this is for a 'training station' for an ATS. You should review the ATS manual to determine what sort of supply it can work with.

Most 480V supplies are 480/277V solidly grounded wye systems. The ATS will certainly be able to work with that. But what you currently have is a 480V ungrounded delta system. You need to check that the ATS will work properly with such a source.

Also, as mentioned elsewhere in the thread, code requires that ungrounded systems have ground fault detection.

-Jonathan

 

[Burdaneta]

Glad you have the voltages correct.

You are still going to need to deal with the issue of grounding your 480V system.

You said this is for a 'training station' for an ATS. You should review the ATS manual to determine what sort of supply it can work with.

Most 480V supplies are 480/277V solidly grounded wye systems. The ATS will certainly be able to work with that. But what you currently have is a 480V ungrounded delta system. You need to check that the ATS will work properly with such a source.

Also, as mentioned elsewhere in the thread, code requires that ungrounded systems have ground fault detection.

-Jonathan

yes thats correct next step is work on the grounding , as for now i connect the ATS and works good.

 

[jim dungar]

Taps moved to number 5 , output voltage A(480), B(479), C(473) , work just great thanks for all your help guys, now we ready to use it.

In a previous post you had two voltages the same and one voltage different, you then changed the taps and you now have three different voltages. I am glad to hear you can use your installation.

When you have a Delta system voltage measure made between two different 'phases', you should list those two points. Actually this would've helpful even when troubleshooting Wye system.

 

[Burdaneta]

In a previous post you had two voltages the same and one voltage different, you then changed the taps and you now have three different voltages. I am glad to hear you can use your installation.

When you have a Delta system voltage measure made between two different 'phases', you should list those two points. Actually this would've helpful even when troubleshooting Wye system.

correct, but is now low or equal to 480v

 

[zbang]

yes thats correct next step is work on the grounding , as for now i connect the ATS and works good.

Grounding/bonding comes before connecting a load, not after!! You may find that the ATS loses it's magic smoke in a couple of days, that won't be pleasant.

 

[DCH_EET_CMPET]

Its been a while but in a 3 phase 208 motor power, leg to leg is 208, leg to ground is 120 right? So, I was looking at 3 phase power transformers. Basic types are Y and Delta. I once had a Missouri Power employee tell me that Delta isnt used but researching it I'm finding that a Delta-Y transformer is used in things which require more power. The inner coils are config in a Delta and the secondary windings are in a Y config. The Y is grounded. I also read that Delta-Delta Xformers are not used much because you cant ground a Delta and still have a Delta. So lets go with a 1-1 Delta-Y xformer, where each leg should be the same on both windings. Its been a while, Graduated 1995 EET, CMPET degrees, and did most my work on LSI factory equipment and Networking using CISCO managed equipment, Virtual Servers, Oracle so my pure electrical theory wasnt used that much except for 3 phase motors using Solidstate relays or SCR Motor controllers. AB controller but Siemens has bought everything. Ive done Allen Bradley PLCs which Siemens bought.. Long ramble to say Im not sure how you can ground a 3 phase - 3 pase xformer and still have 3 equal phases between the phases.

Doogie

 

[motormuff]

Have you bonded grounded your secondary? Try a jumper from your secondary winding to ground, just 1 jumper only. Then reread your voltages.

 

[winnie]

Long ramble to say Im not sure how you can ground a 3 phase - 3 pase xformer and still have 3 equal phases between the phases.

Doogie

You can ground _any_ one terminal of a transformer secondary without changing the voltages between the various terminals. Grounding only changes the voltage between the terminals and ground.

If you have a wye secondary, code requires that you ground the neutral, but physics lets you ground any terminal.

If you have a delta secondary, you have to 'corner ground' the system. The L-G voltages are 0, full, full and not balanced, but the L-L voltages are all normal.

-Jonathan

 

[eric stromberg]

It would be cleaner to use an actual step up. I have bought a number of these. 208 volt delta primary, 480/277 wye secondary.