[SOLVED] K-Rated transformer sizing

Dear sir,

Im trying to model a K- rated transformer to carry the non linear loads .
I tried to size a transformer and i have the following queries :


Core sizing :

1.) while sizing the core should i consider the non linear load current ?
2.) After finding the K-Value based on the linear transformer design the value of K decreases the size of the transformer that is derated than the actual value.
3.)should i design the transformer for Derated capacity ??
4.) Core sizing , If my load consist of non linear loads harmonics is it necessary to add the harmonic current value to the fundamental current to avoid saturation of core ?
5.) When i add the non linear current value to the fundamental current the Apparent power of the transformer size is increased .But in case of k-Rated value the transformer is Derated ???

How would I calculate the Core size for non linear load transformers

Best Regards

Manoj

I presume, all answer can be found in transformer design hand books and technical articles.

I must be confess, that I wasn't aware of the term K-rated up to now, it's simply designating design for harmonic currents.

A brief look at transformer operation principles should reveal, that harmonic currents are not affecting the transformer flux waveform and respectively not the core design. K-rating is mainly about winding losses and winding design. Particularly the term "core saturation" is not related to K-rating.

Harmonic grid load also causes voltage distortion, so as a second order effect, a certain increase in core losses might occur which can be accounted by reducing the core flux by some amount. Also designing the winding for higher harmonic losses can result in a different core to winding dimension trade-off.

Dear sir,

Kindly let me know the Design book related to K- Rated Transformers.

Best regards
Manoj

After reading few Articles i do understand .Due to non linear loads includes the ohmic losses and eddy current losses are increased .Which leads to hot spot temperature in the winding and lead to Failure of insulation and Ageing . So its necessary to derate the transformer .

As , Only the Harmonic current are greately involved rather than Harmonic voltage which is considerabely negligible , so core loss doesnt play any role in the transformer .Hence, Increasing the core size doesnt have any significant effect .

I can notice winding losses are calculated from the previous pre design transformer .the K- value is solved for the Harmonic content and the size of the transformer is reduced .

But, my question is if i want to design a isolation transformer for 6-Pulse drive which consist of h= 5,7,9,11,13...etc after calculating the K value for the particular harmonics and derating .Should i design for the derated value ???

How to size the Transformer ?
How to size the Wire ?
Should i size the neutral conductor ?