Short answer: a fixed speed compressor or motor on the wrong plant voltage needs a standard isolation transformer, for example 600 V to 480 V. A variable speed drive needs a drive isolation transformer, which is built for the harmonic current and DC offset a drive draws. Size both from the motor brake horsepower, not only the nameplate.
The difference
| Isolation transformer | Drive isolation transformer | |
|---|---|---|
| Load | Fixed speed motors, compressors, general equipment | Variable speed drives and VFD compressors |
| Design | Standard dry type, full winding isolation | Delta primary, wye secondary, rated for harmonics and DC offset |
| Main benefit | Matches voltage and isolates the load | Matches voltage and keeps drive noise off the plant system |
| Sizes we sell | 7.5 to 500 kVA | 7.5 to 330 kVA |
Sizing from the motor
Start from the motor brake horsepower and the starting method. Across-the-line starting needs more margin than a soft starter or a drive. The electrical sizing tools turn horsepower and voltage into a kVA and show the matching transformer.
Common Ontario case
Most Ontario plants run 600 V. Much equipment is built for 480 V. A step-down isolation transformer lets you buy the 480 V machine, and the same unit wired the other way steps 480 V up to 600 V.
Can I use a regular isolation transformer on a VFD?
It may overheat from harmonic current and shorten its life. Drive isolation transformers are rated for that duty.
Who installs it?
Installation and connection are done by a licensed electrician. Freight is quoted to your site.
Updated by PRP Reps, Mississauga. Questions about your own system? Send us the duty or call +1 647 717 6264, Monday to Friday, 7 to 5 Eastern.