At present, the problem of measures of the protection against distortion of measured and calculated parameters by signals corresponding to the third harmonic of the mains frequency is quite acute, which is the main parasitic signal entering the distribution networks.The purpose of this study is to develop a technique for reducing distortion caused by the third harmonic frequency in distribution networks.This is achieved by the fact that in each half of the period of the frequencies of the electric network are additionally determined by the times corresponding to 5/6, 4/6, 2/6,1/6 of its part, measure the value of the measured signal at each additional time, sum the values obtained in the main and additional moments in n adjacent halves of the period, calculate the average amplitude value of the signal for n adjacent half periods, and the average amplitude value of the measured signal is obtained by dividing the obtained value by a coefficient equal to 1+√3/2+ 1/2.

Keywords: measurement error, distribution grid, third frequency harmonic, device for measurement and calculation of electrical parameters