Transformers and Drives - sizing and harmonics

AI Thread Summary
When using transformers with three-phase drives for induction motors, it is often suggested that transformers should be sized 40% larger than the drives to mitigate harmonics and other issues. However, this sizing can vary significantly based on the quality of the variable frequency drives (VFDs) and the filtering applied. The discussion highlights that there is no universally accepted standard or reliable recommendation for transformer sizing relative to drives, as each installation is unique. The 40% guideline may serve as a precautionary measure rather than a strict requirement. Ultimately, careful consideration of specific application needs and engineering analysis is essential for optimal transformer sizing.
elcraft
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Hello,

Is it true that when using transformers and three-phase drives/VFDs for induction motors, the transformer's power needs to be much higher (e.g. +40%) than the drive's in order to avoid increased harmonics (or even other problems)?

If you know any official standard, paper or recommendation regarding the matter of sizing transformers vs drives, please share.

Thank you.
 
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It is a very generalized question - there is a pretty big range in quality of VFD and the types / amount of filtering that can be applied. -- So the "needs" question could be "may need" - However, every installation or application is different.
Regardless 40% seems like a lot, but depending on who you got your info from - they may have learned that spec'ing a 40% larger transformer is insurance against problems, and has worked in the past without looking at the causes or doing real engineering.
 
So there is no paradigm with reliable recommendations or relevant discoveries?
 

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