480 - 240V Transformer check. 1

[itsmoked]

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?




Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Thanks for the information, Jeff.

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.

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
--------------------
"Why not the best?"
Jimmy Carter

 

[prc]

IEEE standard for solar transformers C57.159-2016 where under clause 5.1.4 quote -The inverter operation is not affected by the inverter transformer vector group (Dy1, Dy5, or Dy11 will make no difference). No neutral connection is required on the primary (LV) side of the transformer. If a neutral point of the primary (LV) winding is available, it is recommended that this neutral point is neither grounded nor connected to other ground points. On the secondary (HV) side, the inverter transformer can have an isolated neutral point or resonant grounding or low resistance grounding -unquote

 

[waross]

This looks like two issues combined in one paragraph.
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:

If a neutral point of the primary (LV) winding is available, it is recommended that this neutral point is neither grounded nor connected to other ground points.

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
--------------------
"Why not the best?"
Jimmy Carter

 

[prc]

Waross, in all those combinations HV is usually delta connected. Only LV where power is fed is star and the neutral will be floating. This is opposite to normal step up transformers where power is fed to delta LV and HV star neutral is earthed.(YNd1 or Ynd11)