Transformers and Drives - sizing and harmonics

In summary, when using transformers and three-phase drives/VFDs for induction motors, it is recommended to have the transformer's power be at least 40% higher than the drive's to avoid potential problems such as increased harmonics. However, this may not always be necessary and depends on the quality of the VFD and its filtering capabilities. Currently, there is no standard or official recommendation for sizing transformers versus drives, and it may vary depending on the specific application.
  • #1
elcraft
8
0
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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  • #2
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.
 
  • #3
So there is no paradigm with reliable recommendations or relevant discoveries?
 

Related to Transformers and Drives - sizing and harmonics

1. What is the purpose of sizing transformers and drives?

The purpose of sizing transformers and drives is to ensure that they are capable of handling the required load and meeting the power demands of the system they are being used for. This involves calculating the appropriate size and capacity of the transformer and drive based on the specific application and load requirements.

2. What factors should be considered when sizing transformers and drives?

When sizing transformers and drives, factors such as the type of load, power demand, voltage and current ratings, efficiency, and environmental conditions should be taken into account. It is important to also consider any potential harmonics that may be present in the system, as these can impact the performance and lifespan of the transformer and drive.

3. How are harmonics addressed in the sizing of transformers and drives?

Harmonics can be addressed in the sizing of transformers and drives by using specialized software tools to analyze the system and identify potential harmonic issues. This allows for the selection of transformers and drives with appropriate ratings and filtering capabilities to mitigate the effects of harmonics on the system.

4. What is the importance of considering harmonics in the sizing process?

Considering harmonics in the sizing process is important because they can cause issues such as overheating, voltage distortion, and power quality problems in the electrical system. By properly addressing harmonics in the sizing of transformers and drives, these issues can be avoided, ensuring the safe and efficient operation of the system.

5. Can transformers and drives be oversized for a particular application?

Yes, transformers and drives can be oversized for a particular application. However, this can lead to increased costs and reduced efficiency. It is important to carefully consider the specific requirements and load demands of the system when sizing transformers and drives, to avoid unnecessary oversizing.

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