Delta-Delta Transformer

[Joethemechanic]

86.6% tab is used on the primary side not the secondary

Where did I say it wasn't on the primary?

one pole pig with the primary tapped at the 86.6%

open delta, causes two sets of current current to flow through the A-N windings of the transformer.

Open delta is my own personal service here at my shop where I almost never have a two phase load and if I do it might be 10 HP at the most and probably never drawing FLA.

And if we close the delta, now we have two paths and lessen the transformer secondary impedance issue.

Believe me guys in philly that have a couple old 2 phase machines don't use them much, usually it's something specialty, not like it's a production machine with a guy on it 8 hours a day. Not everyone is some big corporation that would install a Scott T in order to power one 85 year old 15 HP machine tool that gets used 4 hours a week.

 

[jim dungar]

I understand 2 phase power as well as transformer construction.

The 86.6% tap is on the primary of a Scott-T it is not on the secondary side which provides 240V to the load. In the case of a high leg system the 208V is being fed to the loads.

You do not need to convince me that 2-phase motors can be run off of 3-phase high leg systems as long as the loss in performance is acceptable. But I will not accept it as a preferred permanent installation for fully loaded motors.

 

[Joethemechanic]

I understand 2 phase power as well as transformer construction.

The 86.6% tap is on the primary of a Scott-T it is not on the secondary side which provides 240V to the load. In the case of a high leg system the 208V is being fed to the loads.

You do not need to convince me that 2-phase motors can be run off of 3-phase high leg systems as long as the loss in performance is acceptable. But I will not accept it as a preferred permanent installation for fully loaded motors.

Yeah the primary is 86.6 because the voltage at the two points that it is connected to is 86.6% of what phase to phase voltage is. Basically the height of an equilateral triangle is 86.6% of any side.

There still are a lot of two phase buildings in Philly with Scott-T connections. Not many industrial two phase customers though. Last one I worked on was The Youth Study Center (kid's jail). Three phase 480v emergency generator feeding a Scott-T with 120/240 five wire secondary, and a two phase ATS. Nobody can waste money like the government

 

[Grouch1980]

We've used this type of transformers once when we needed 3 phase, 240 volts and no neutral. The advantage is you still have a grounded system.

Would you have a cutsheet of this type of transformer? I'm assuming it's allowed for use in NYC. (just making sure there's no surprise code section )

 

[Grouch1980]

I found one:

3-Phase 480 D - 240 Y 139 (Drive Isolation Transformer)

Drive-Isolation transformer converts 3-Phase 480D to 240Y/139. These units can handle demanding AC/DC variable speed drives and provide needed voltage change.

www.maddoxtransformer.com

It says it's a drive isolation transformer. Is this strictly designed to feed VFD type loads, or can this transformer feed any type of 240 volt line-line loads?

 

[jim dungar]

I found one:

3-Phase 480 D - 240 Y 139 (Drive Isolation Transformer)

Drive-Isolation transformer converts 3-Phase 480D to 240Y/139. These units can handle demanding AC/DC variable speed drives and provide needed voltage change.

www.maddoxtransformer.com

It says it's a drive isolation transformer. Is this strictly designed to feed VFD type loads, or can this transformer feed any type of 240 volt line-line loads?

It can feed any load.
For the past couple of decades a drive isolation transformer is more marketing than anything else. Back in the days before diode bridge front ends, drives had a high propensity to produce harmonics that had the potential to cause excessive heating in transformers and interference with other equipment. These issues were often mitigated by a grounded Wye secondary in a transformer built to handle additional heating.

 

[Grouch1980]

It can feed any load.
For the past couple of decades a drive isolation transformer is more marketing than anything else. Back in the days before diode bridge front ends, drives had a high propensity to produce harmonics that had the potential to cause excessive heating in transformers and interference with other equipment. These issues were often mitigated by a grounded Wye secondary in a transformer built to handle additional heating.

would this be a better transformer for what I need? my primary is actually 460 volts (Con Edison voltage). The motor load is rated 220 volts. This transformer has a 460 volt primary, with a 230 volt secondary; the secondary is much closer to the 220 volt motor rating. And assuming voltage drop, the transformer might actually be delivering somewhere around 220 volts:

3-Phase 460 D - 230 Y 133 (Drive Isolation Transformer)

Drive-Isolation transformer steps down 3-Phase 460D to 230Y/133. These units can handle demanding AC/DC variable speed drives and provide needed voltage change.

www.maddoxtransformer.com

 

[Grouch1980]

And my next question, are there any limitations with using these transformer voltages? Are they allowed to be used anywhere? I'm in the NYC area. I'm so used to working with 277/480 volts and 120/208 volts, I've never worked with these other voltages (139, 133, etc.).

 

[LarryFine]

would this be a better transformer for what I need? my primary is actually 460 volts (Con Edison voltage). The motor load is rated 220 volts. This transformer has a 460 volt primary, with a 230 volt secondary; the secondary is much closer to the 220 volt motor rating. And assuming voltage drop, the transformer might actually be delivering somewhere around 220 volts:

3-Phase 460 D - 230 Y 133 (Drive Isolation Transformer)

Drive-Isolation transformer steps down 3-Phase 460D to 230Y/133. These units can handle demanding AC/DC variable speed drives and provide needed voltage change.

www.maddoxtransformer.com

Motors are rated below nominal voltages for exactly that reason. It looks like a good choice.

 

[LarryFine]

A high-leg delta is a standard 1ph 120/240v source AND a standard 3ph delta source, superimposed on each other. In fact, the high-leg, open-delta service originated as a modification to existing 1ph services for new 3ph equipment.

 

[Isaiah]

You still need grounding electrode connections and a SSBJ per 250.30(B) and you will need ground fault detection per 250.21(B)
You will not have a SBJ.

Does the SSBJ simply connect from the XFMR enclosure to the Panel or Disconnect enclosure since there is no neutral ?


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[don_resqcapt19]

And my next question, are there any limitations with using these transformer voltages? Are they allowed to be used anywhere? I'm in the NYC area. I'm so used to working with 277/480 volts and 120/208 volts, I've never worked with these other voltages (139, 133, etc.).

The only limitation is the line to neutral voltage. It can supply any type of line to line loads.

 

[don_resqcapt19]

Does the SSBJ simply connect from the XFMR enclosure to the Panel or Disconnect enclosure since there is no neutral ?


Sent from my iPhone using Tapatalk

The only difference between the grounding and bonding requirements for a grounded or ungrounded separately derived system is that the ground system will have a system bonding jumper and the ungrounded system will not have a system bonding jumper.

 

[tortuga]

I have also seen 220Y127 transformers for this. If you have a tap changer on a 208 bank you can get 220Y127.

 

[Birken Vogt]

Mexico runs 220/127Y for residential services I understand.

I do a lot of trailer mount gensets that are permanently wye connected. We set them up as 240/139 if no single phase loads, 220/127 if we need to "split the difference", or 208/120 if the low voltage loads are thought to be sensitive.

Our shop is 240 open delta as well. Interestingly, the neighboring building on the same tx bank has no 3 phase loads but has 2 different single phase 240 loads on two different sides of the delta including the phantom one.

 

[tortuga]

Mexico runs 220/127Y for residential services I understand.

Mexico all the way down to Argentina uses it now. The US and Canada are the last places using 208Y120.
The interesting thing is now that incandescent is phased out, I bet that in 20 years 127V will be more widely used than 120V if its not already.