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Steven MillParticipant
@guest said:
very interesting article…bt tell me abt fuzzy logic and lfc
Thanks. I’ll write an article about LFC, you could read it at the beginning of next week.
Steven MillParticipantHello, you’re welcome!
Jeff Williams, sure next week I’ll post an article about AGC first.
Steven MillParticipantThank you for your feedbacks!
Spir Georges GHALI, sorry for the late reply and thank you for your interesting remarks.
@Spir Georges GHALI said:
Dear;It’s very good and important to mention the effects of Harmonics on the Transformers, but I have some remarks that are :
– I think the percentages of Harmonics currents mentioned in this topic mean the percentage of the “ THDI ” ( Total Harmonic Distortion of Current ). If not, please clarify.
Yes these percentages are of THD. Sorry If that confused you.
– It’s known that the effect of KFactor is to oversize the Transformer’s power, but what is the formula between the KFactor and the Transformer’s power ?
Normally in order to calculate the KFactor you keep into account two things the KVA & load Harmonic Current. So accordingly the KFactor would be:
K – Factor = KVA * I_{L}
As I_{L} is the load harmonic content so you can easily calculate the KFactor value to be used.
– You mention that “ the inductive loads like Motors are known as harmonic generating loads ”, but most of motors especially “ Squirrel Cage Motors ”, and after the transient running case are always “ Linear Loads ”, but for these loads the Harmonic currents can be generated or not depending on the kind of running equipment used to run these motors. ( for exp. Contactors with Thermal relays doesn’t generate any harmonic, VFD equipment generates harmonics ).
I was specifically referring to induction motors which are widely used in industry as compared to squirrel cage motors which are most suited for small tasks. Very rare have I seen squirrel cage motors used in industry. Induction motors generate harmonics and come in the domain of nonlinear loads. Also in industries the Switch mode power supplies & DC rectifiers also add to the nonlinearity of the system.
– It’s mentioned that “ the working principal of Krated Transformers involves the use of a double sized neutral conductor ”, but in general, depending on the Harmonics Currents value or percentage, we oversize “ double or even more ” the cables’ sections of Phases & Neutral “, and also depending on the value or percentage of the “ Third multiple Harmonics ” and the “ Unbalance current’s value ” we decide the final section of neutral conductor.
Yes you are right about conductor size. It depends on the harmonic currents value. I also wrote in the article that Some Krated transformers use more than one conductor. Normally you don’t need a transformer with Kfactor rating more than K4 or K13 in industries which are coherent to the design specs presented in the article.
– As mentioned, the KFactor Value’s range is from “ 1 ” to “ 50 ”, and also, the rules mentioned the KFactor Transformers that should be used depending on the Harmonic Current, ( exp. for Harmonics Currents more than 75% the “ K20 Transformers ” should be used ) but, at which levels or where the values “ K30 or K35 Transformers ” or more should be used ?
Transformer size increase as you increases the value of KFactor & so does the heat tolerance due to harmonic currents. Normally transformers of KFactor 30, 40 & 50 are used where harmonic currents are somewhere b/w 125150%. These are worst harmonic conditions. As mentioned before the size of transformer increases with the increase in KFactor so the optimal KFactor should be chosen which would be a tradeoff between transformer size & its heat tolerance. Normally the K50 transformers are very expensive & much larger in size so manufacturers recommend a transformer of K30 with modified designs as a replacement.

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