Feeding 120/240V high leg delta to 208V transformer

[housemoney]

Have loads rated 230-480V 3 phase- no neutral required. These loads will not accept 120/240V high leg delta.

In lieu of going 240V delta to 480V Wye, the transformer proposed nameplate is below, I have my doubts on this setup (temporary maybe?) but have never fed this way before. Thoughts?

 

[winnie]

You state that the load will not work with a high leg delta. Since _most_ delta loads work fine with any 3 phase supply (wye, corner grounded delta, high leg, floating...) this implies that you have one of those loads that really needs a grounded wye source. This is usually because of ground references in the system. (TVS devices on a VFD, for example)

The transformer you show is a 208V Delta to 208/120V wye unit. It might function as the 240V D to 240/139V Y that you need, but the overvoltage will likely saturate the core, causing excess heat and harmonics. The supply is >12% 'hot' for the transformer.

Jon

 

[housemoney]

You state that the load will not work with a high leg delta. Since _most_ delta loads work fine with any 3 phase supply (wye, corner grounded delta, high leg, floating...) this implies that you have one of those loads that really needs a grounded wye source. This is usually because of ground references in the system. (TVS devices on a VFD, for example)

The transformer you show is a 208V Delta to 208/120V wye unit. It might function as the 240V D to 240/139V Y that you need, but the overvoltage will likely saturate the core, causing excess heat and harmonics. The supply is >12% 'hot' for the transformer.

Jon

Yes loads are high speed door operators with integral VFDs. Literature doesn’t specify grounded wye source required, just that 120/240 high leg Delta and any phase converters are incompatible.


Very light, short time loads- So I’d imagine the saturation issue can be avoided?

 

[synchro]

Very light, short time loads- So I’d imagine the saturation issue can be avoided?

Core saturation is not related to the applied loads, but to the applied voltage on the primary. Saturation will occur with no loading at all if the primary voltage is higher than the transformer can handle.

 

[housemoney]

You state that the load will not work with a high leg delta. Since _most_ delta loads work fine with any 3 phase supply (wye, corner grounded delta, high leg, floating...) this implies that you have one of those loads that really needs a grounded wye source. This is usually because of ground references in the system. (TVS devices on a VFD, for example)

The transformer you show is a 208V Delta to 208/120V wye unit. It might function as the 240V D to 240/139V Y that you need, but the overvoltage will likely saturate the core, causing excess heat and harmonics. The supply is >12% 'hot' for the transformer.

Jon

Digging a little deeper here, a photo of the load's inside cover also mentions: "clean power source" being required. They appear to be 100% solid state design (line terminals landing on a PCB, not on the VFD) with no line reactor or any sort of harmonic suppression or front end protection on the tiny VFDs.

Would you agree that said transformer, if saturated, would probably operate the loads but could potentially causse damage by supplying excessive harmonics to the load? If so, would my original plan of going with a boost transformer from 240V:480V suffice? I have not run into anything like this previously and appreciate the help!

 

[winnie]

I have no practical experience running a 208V rated transformer on 240V. I don't know if the transformer would simply run hot because saturation would cause excessive magnetizing current to flow, or if you'd let the smoke out. If the transformer ran and didn't get too hot, I'd expect saturation to distort both its input and output waveforms.

IMHO your choice is either a 240V DELTA to 240/139V WYE transformer _or_ a 240V DELTA to 480/277V WYE transformer.

You seem to be using the term 'boost' to mean 'step up' transformer. The term 'boost' is generally used for an autotransformer configuration which would not be suitable. But if you mean 'step up isolation transformer' then I agree it would be a good choice.

Depending on the value of the hardware you might want to look for a 'drive isolation transformer', which is a transformer specifically designed for feeding VFDs.

Finally, in no case use a standard step down transformer 'in reverse' for this application.

-Jon

 

[Jraef]

IMHO your choice is either a 240V DELTA to 240/139V WYE transformer _or_ a 240V DELTA to 480/277V WYE transformer.

Winnie is correct, these are your only viable choices. The 240V Delta to 240Y139V is commonly available, they are called “Drive Isolation Transformers” when you go to search for them. They are specifically for this purpose; providing a grounded Wye source for the drive because it is not an uncommon issue for 240V drives.