Re: volt and current harmonics

Spir Georges GHALI

jatin333 said:

up what extent voltage and current harmonics acceptable?

what are effects of current and volt harmonics in system?

Dear Mr. Jatin333 ;


refer to your question and the reply of Mr. Alen, I want to clarify some points :

1 – We know all that the path of any current either Fundamental or Hamonic current is from the load to the source, that means there's no any direct effects from the harmonic currents on the other loads, but, the harmonic currents with the harmonic inpedance of network are reponsable to have a ” Voltage Distrotion ” in the network, and that voltage distortion has a direct effets on the loads even the linear-loads. So, the effetcs of the harmonics current is, as Mr. Alem said, on the : Cables, Transformers, Generators, Motors, Capacitors, ext. where there's many solution for that.


2 – Normally, as the direct effects on the load is from ” Voltage Distortion ” we should look to the percantage of Voltage Harmonic that means ” THD U  or  THD V “, and when these values exeed some levels, we should find the suitable solution for the network, else we will have problems with some sensitive equipments. Noting that when the ” THD I ” incraese the ” THD U ' will increase also, but be carfull even if we have the same percentages of ” THD I ” in 2 different networks it's not necessary to have the same percantage of ” THD U ” for both, because it dependes on the value of the ” Harmonic Impedance ” of each network.


3 – In some time when the level of Voltage distortion is smaller than standard or definded value, we can accept, as THD I, till ” 40-45% “.


4 – For information, the ” IEC 61000,2 ” defined the percantage of Harmonic Voltage for each harmonic ” Odd & Even harmonics ” in LV networks, and also in some countries the Electricity Co. define the ” THD U ” for their :V & MV networks.




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