480 - 240V Transformer check.
480 - 240V Transformer check.
(OP)
I have 480V 3ph (about 40kVA) and need to hook up a 230V machine. We're looking for a transformer and I believe we want a Delta-Delta and not a Delta - Wye. The machine has no neutral connection.
Seems we can find lots of Delta - Wye here about. I should probably hold out for a delta secondary right?
Seems we can find lots of Delta - Wye here about. I should probably hold out for a delta secondary right?
Keith Cress
kcress - http://www.flaminsystems.com






RE: 480 - 240V Transformer check.
RE: 480 - 240V Transformer check.
Keith Cress
kcress - http://www.flaminsystems.com
RE: 480 - 240V Transformer check.
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: 480 - 240V Transformer check.
In Canada (And probably the US) grounding the neutral is a code requirement at that voltage.
Look for a 240 Volt secondary. 480:139/240 Volts.
More common is 480:120/208 Volts. That may be a little low foe your machine.
The problem connection is the grounded wye/delta connection. The four wire primary connection locks in the phase angles and voltages and the delta secondary is unable to willingly accept any unbalances.
With the delta/delta the angles and voltages are not constrained and the secondary is free to track primary unbalances.
If you are unable to locate a delta/wye transformer with acceptable voltages, your second choice may be two 480:240 Volt ransformers in an open delta configuration.
Third choice may be a 480:120/240 Volt four wire delta with the center tap grounded.
Bill
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"Why not the best?"
Jimmy Carter
RE: 480 - 240V Transformer check.
http://www.practicalmachinist.com/vb/attachments/f...
In the US you could go delta ungrounded, but you need a ground detector and in all honesty its best not to bother.
Some machines like VFDs do not life floating voltages- or one leg elevated- so make sure you double check that if you go the delta route.
RE: 480 - 240V Transformer check.
RE: 480 - 240V Transformer check.
RE: 480 - 240V Transformer check.
If there are no 3 phase rectifiers involved, I wouldn't use the non-standard voltage, because Murphy dictates that some future goober will read 240V L-L and ASSume it is 120V to N, then fry something.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: 480 - 240V Transformer check.
RE: 480 - 240V Transformer check.
RE: 480 - 240V Transformer check.
That is, power in to the wye side and power out the delta side.
That is a special case that often leads to issues in practice.
The issues may be avoided by floating the wye point.
Bill
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"Why not the best?"
Jimmy Carter
RE: 480 - 240V Transformer check.
Indeed 240 wyes are not common. Most of these machines are actually made with a nameplate supply number of 220V. Which gets you into 'trying' 208V. Some are tolerant and don't care but others monitor the voltage and 'tilt' if it drops much below. What happens is when the machine starts a non-VFD'd motor like a coolant pump or hydraulic chiller it causes a brief dip that is enough to cause the already low 208V to dip below the trip and the controller stops on an error which requires human intervention to continue.
Thanks all.
Keith Cress
kcress - http://www.flaminsystems.com
RE: 480 - 240V Transformer check.
'That is a special case that often leads to issues in practice.
The issues may be avoided by floating the wye point.'- can you explain this a bit more? Why modern inverters find delta source not compatible?
RE: 480 - 240V Transformer check.
Probably the most available transformers will be 480:208/120 Volts.
You can use three three small 120:12 Volt or three 120:16 Volt transformers to boost the line to line voltage to 228 Volts or 236 Volts.
The current rating of the 12 Volt or 16 Volt windings need only be 1.73 times the needed current.
Yes, it's a little kludgey but it may be what is available at a reasonable price.
The other option may be the delta:delta with a four wire 124:240 Volt secondary with a "wild leg and a grounded center tap.
jraef; How do VFDs respond to a high leg system. The voltages to ground will be 120V, 120V and 208 V.
Bill
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"Why not the best?"
Jimmy Carter
RE: 480 - 240V Transformer check.
Kinda sad cuz the place has a ton of 460 drops everywhere but 90% of their machines are 220V. I'd prefer just switching all drops to new machines over to 240 but then the wire is probably too small, but then the conduit probably can't stand the bigger wire, so now you have to yank a bunch of 250 foot runs of conduit off a 40 foot ceiling and replace it all with larger everything.
So the solution seems to be putting a transformer next to each machine so you can heat the local space, trip over the dang things, and have to make more room for them.
Non-optimal - painted gold.
Keith Cress
kcress - http://www.flaminsystems.com
RE: 480 - 240V Transformer check.
I don't work with the NEC but there is a lot of similarity with the Canadian Code.
I realize that the Canadian Code does not apply but hopefully someone will supply the NEC equivalent.
There are significant differences between equipment grounding conductors and system neutral grounding conductors.
In Canada if a grounded neutral of a system results in voltages to ground of 150 Volts or less then the neutral must be grounded.
A delta:wye transformer would be considered a separately derived system and would require a system ground. It is doubtful that the equipment bonding conductor will meet code for a system ground. The installation requirements for a system grounding conductor are more stringent than the requirements for an equipment bonding conductor.
The nice fix voltage wise is a two transformer open delta auto-transformer connection.
The voltages to ground will be 277 Volts, 139 Volts and 139 Volts.
The advantages are:
Cheapest.
Smallest.
Does not require a neutral.
Does not require a system ground.
Bill
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"Why not the best?"
Jimmy Carter
RE: 480 - 240V Transformer check.
As I said, the way to find these transformers that will have a 230V Y secondary is to look for "Drive Isolation Transformers". In the following linked document, see page 5 of the PDF (referred to as page 127), part #DM040JC
http://www.hammondpowersolutions.com/files/HPS-Sta...
Pretty much ass of the major transformer mfrs offer similar products, you just need to look in the right places.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: 480 - 240V Transformer check.
In many Canadian plants an additional system grounding conductor would have to be run to remote mounted transformers in addition to an existing equipment grounding conductor.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 480 - 240V Transformer check.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: 480 - 240V Transformer check.
In Canada, these conduit runs would either have equipment bonding conductors or in some instances the conduit may serve as the bonding conductor.
Our code allows normal splices in bonding conductors but is very restrictive of splices in system grounding conductors.
The sizing criteria is also different.
In most plants we would have to run new system grounding conductors to meet code.
Hence my question regarding the effect of voltages to neutral/ground of 277V, 139V, and 139 Volts.
Your solution is the acknowledged best way to go in most instances Jeff.
However, if Keith is faced with running hundreds of feet of system grounding conductors, it may be well to investigate the usability of an alternate solution.
Another option may be to use three transformers connected as wye autotransformers. This would give 240 Volts with equal voltages from line to ground.
Bill
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"Why not the best?"
Jimmy Carter
RE: 480 - 240V Transformer check.
RE: 480 - 240V Transformer check.
Issue #1.
The vector group does not matter.
Issue #2
Grounding the wye point, if available.
This mentions possible wye points on both the primary and the secondary sides.
Dy1, Dy5, and Dy11 do not have a neutral on the primary side.
Thank you, prc, for bringing this recommendation to our notice:
Note: If a wye:delta configuration must be used for special circumstances, it is strongly recommended that the primary wye point be left floating.
This applies to any installation, not just solar installations.
Bill
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"Why not the best?"
Jimmy Carter
RE: 480 - 240V Transformer check.