DETERMINATION OF THREE-PHASE VOLTAGE S UNBALANCE WITH THE USE OF ANALOG-DIGITAL CONVERTORS OF ITS INSTANTANEOUS VALUES AND MATHEMATICAL TREATMENT OF THE GOT CODES

Abstract

Appearance of the asymmetrical, impulsive and stochastic loadings, store inter capacitors and semiconductor modulators in three-phase networks (3phn) substantially worsens their indexes of electric power quality, in particular such static and dynamic indexes, as voltage unbalance, speed and size of its change. Development of analog-digital measuring devices for determination of unbalance of three-phase voltage of fundamental frequency is an complicated problem, as analog blocks and analog-to-digital converters of the phase channels must be realized with identical parameters. For decreasing the parameters dispersion error of phase channels it is being suggested to measure phase voltages instantaneous’ values at the output (a, b, c) clamps of the phase channels simultaneously during a period (20 ms) and to memorize it. Farther the input (A, B, C) and output (a, b, c) clamps of the phase cannels are being switched "on a ring" with a phase step of 120⁰. All the operations mentioned above are being executed three times. Thus a vector error caused by dispersion of parameters of the phase channels of measuring device is also being revolved with a phase step of 120⁰, and the vectors of the negative voltage sequence (NVS) of the fundamental frequency (NVSFF) of the 3phn are not being revolved. Therefore the next adding of the proper instantaneous values of different three tacts selects the instantaneous values of triple NVSFF of the 3phn without the parameters dispersion error of phase channels.  References 12, figures 3.