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**paule said: **

Is there any value per standard to use as reference for Total Harmonic in the system. What is the value we can say it is safe for a sensitive instrument.

Need to educate me, how the hamonic and distortion is appearing in the electrical system?please need your expert advice, thanks

Dear Paule ;

First, the harmonics currents are generating by the Elctronics Loads like : Computers, Printers, Faxes machines, Variable Speed Drives, DC Drives, Electrnic transformers for lighting, ext. These loads generates the Harmonics Currents, and all distortion of currents we called ” THD I – Total Harmonic Distortion of Current ” that affacte the voltage sine wave ( becuase we have the Harmonic Impedances ), so, we have that we called the distortion of Voltage ” THD U or THD V “. Noting that the most importatnt value is ” THD U or THD V “.

The ” IEC 61000-2-2,3,… ” defines the maximim percantages value of Voltage Distrotion of each harmonic for ” HV, MV, and LV networks, for exp. for LV networks : for n=3, the maximum is ” 5 % “, for ” n=5 ” the max is ” 6 % “, and also this IEC… defines these percantages for Odd & Even Harmonics. In France, the EDF defines the max percantage of ” THD V ” on the LV networks by ” 5 % “.

Regards.