3 phase transfor connections
- Thread starter craigo321
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- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
No.
You can use use any transformer arrangement to go from 1-phase to 120/208. To get this voltage you need a 120? phase shift.
Do you need really 208V L-L? Can you use a standard 120/240V arrangment and then 'buck' the 240V to 208V?
You can use use any transformer arrangement to go from 1-phase to 120/208. To get this voltage you need a 120? phase shift.
Do you need really 208V L-L? Can you use a standard 120/240V arrangment and then 'buck' the 240V to 208V?
Being an "emergency" temporary situation, he likely doesn't have a buck transformer handy. If the transformer has voltage taps, could he use two primary windings to develop <120-N ? 2, >208 L-L, but close enough secondary voltage?
PS: If the secondary system is 120/208V 1? (which is a misnomer for partial 3? wye), I'm wondering why he does not have 480V 3????
PPS: We are assuming the transformer's primary is 480V delta and the secondary is 208/120V... he didn't really specify.
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- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The OP said single phase primary. There is no way to get 208V from the output of wye connected transformer windings, if you only feed them with single phase.
The OP said 480 delta 3? transformer.
craigo321 said:
Again, I have to ask why 480V 1?? Is 480V 3? available? Is one or two primary windings shot? ... questions, no answers!!!
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- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Read the entire OP.
It said 3-phase transformer and single phase primary.
My assumption is they have lost their 3-phase supply for a period of time, and would like to continue to supply the existing 120V and 208V equipment.
The answer is no, you cannot replicated the 120V and 208V relationships with only a single phase primary.
A standard 3-phase delta-wye transformer has fixed winding interconnections, so the possible output voltages are limited.
Connecting 480V 1? to two windings of a delta-wye 3? transformer is a single phase primary.
My assumption as well.
I'm not saying the connection I suggest will replicate 120/208V 1? 3W.
I know. You suggested 120/240V 1? 3W (with a buck transformer). Just how do you propose to get that 120/240 from a 480D:208Y/120 3? transformer? Wouldn't you have to connect 480V 1? to two primary windings? So you'd get 120/240V 1? 3W off the two mating secondary windings. Correct?
What I'm saying is if the primary has voltage taps (i.e. they are usually on the primary), connect to the highest voltage taps so it reduces the secondary voltage to something below nominal for L-N, and the L-L voltage will double that... it will be higher than the nominal 208, but both voltages (L-N and L-L) would be within acceptable tolerances.
Okay, here's a typical 480 to 208/120 transformer connection diagram...
Connect 480V L1 to H1, L2 to H2 and H3. H1 and H2 Jumpers to their respective Tap 1 (504V tap).
504V to 120V is a 4.2:1 ratio. With a 480V actual voltage input, the output voltage of X1 to X0, and X2 to X0 should be 480?4.2=114.3V. Voltage across X1 to X2 should be 114.3?2=228.6V. 114.3V is greater than 90% of 120V (108V), while 228.6V is [barely] less than 110% of 208V (228.8V).
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kwired
Electron manager
- Location
- NE Nebraska
If it is temporary rent, borrow, steal (ok maybe not steal) a generator with needed output. Will likely cost less than purchasing transformers needed - especially if capacity needs are high enough.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Connecting the single phase 480V across two primary windings will result in in the windings being in parallel this will mean each winding sees 50% of the input voltage so the output will also be only 50%.
If you connect two of the windings in parallel (i.e. jumper C->B, and then feed 480V to A and B/C) you will get about 120V from two of the secondary windings. However, because you have changed the intended relationship between the primary H1-H2-H3 and X1-X2-X3 terminals the (2) resultant 120V outputs will not combine to create 240V.
Connect to two primary windings, 480V each.
Please examine the following diagram carefully...
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
My bad, the outputs would be additive, effectively X1->X0->X3.
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