Reliance VFD & Transformer

ptonsparky

Senior Member
Yesterday we replaced an older Reliance VFD that was used on a 10HP motor. A Delta to Delta reverse fed transformer was used to take the utility supplied 240v hi leg, to 480v.

What would be the reason for it? Were 240v units that much larger or more expensive at the time?

We installed a 240v unit.
 

JDBrown

Senior Member
No idea about the price of VFD's at different voltages, but I would guess the reason for using 480V was either:

1. Somebody already had a 480V VFD on hand, and it was cheaper to buy a transformer than a 240V VFD;

OR

2. Somebody bought a (non-refundable) VFD with the wrong input voltage rating, and it was cheaper to buy a transformer than to replace it with a VFD at the correct input voltage.
 

Jraef

Moderator
Staff member
No idea about the price of VFD's at different voltages, but I would guess the reason for using 480V was either:

1. Somebody already had a 480V VFD on hand, and it was cheaper to buy a transformer than a 240V VFD;

OR

2. Somebody bought a (non-refundable) VFD with the wrong input voltage rating, and it was cheaper to buy a transformer than to replace it with a VFD at the correct input voltage.
Or

3. It was a 460V only motor, not easily replaceable and not wound for dual voltage. But if you have now replaced it with a 240V drive, I guess not. Motor might have been replaced since the original install though.

Generally, 240V drives are cheaper than 480V drives HP to HP even though the current is higher, because the transistors and diodes for 300V and below are much less expensive.
 
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ptonsparky

Senior Member
Never thought about somebody just having a BF, I should have, nothing else about the install was correct. It did work for 15 years +-, so good enough I guess.
 

jim dungar

Moderator
Staff member
What would be the reason for it? Were 240v units that much larger or more expensive at the time?
A Reliance drive would be relatively old. Back in the 'early days' of VFDs (20years ago), it would not have been uncommon to see a delta-delta 'drive isolation transformers' used in a mistaken effort to keep this small 10HP drive from interferring with the building's power grid (those damn harmonics). Seeing how they had to buy the transformer, purchasing a smaller 480V drive and motor combination may have made sense, both economically and installation wise.
 

ptonsparky

Senior Member
Alright!! I now have a recycled "drive isolation transformer" in stock and ready for sale. Make a good boat anchor.
 

Jraef

Moderator
Staff member
Alright!! I now have a recycled "drive isolation transformer" in stock and ready for sale. Make a good boat anchor.
Meh, they are still a good idea for older DC drives, you never know when you might need one.

But then again, I have a garage and a shed FULL of that sort of stuff, it may end up being the cause of my divorce some day...
 

Besoeker

Senior Member
Meh, they are still a good idea for older DC drives, you never know when you might need one.
Well, we've been making DC drives for years and we haven't used isolation transformers. It seems to be more of a North American practice.
Where we have used transformers it has been the need to change the voltage or for 12 and 24-pulse systems.
 

ptonsparky

Senior Member
Well, we've been making DC drives for years and we haven't used isolation transformers. It seems to be more of a North American practice.
Where we have used transformers it has been the need to change the voltage or for 12 and 24-pulse systems.


That makes it even more odd because I live in Nebraska, not North America.












:jawdrop:. :DJK
 
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