### RESEARCH OF THE REASONS FOR THE APPEARANCE OF HIGHER HARMONICS AND STRUCTURE OF THE COEFFICIENTS OF NON-SINUSOIDAL CURRENT AND VOLTAGE FEEDING NETWORK ENTERPRISE WITH ROLLING PRODUCTION

#### Abstract

As an object of study was taken unit section a power supply at the rolling shops of a metallurgical plant with substation a deep input 150/10 kV, which feeds three shop substations.

Information was measured and processed mainly by a microprocessor complex ANAYST2Q (company LANDIS&GYR), the complex allowed to record higher harmonics of voltage and current up to the 25th harmonic inclusive, harmonics from 2 to 40 were measured with harmonic analyzer 43250. Measurements were carried out over several days with different loads.

The measurement of harmonics in normal modes showed the following: the second and third harmonics show little in the spectrum, that is the average values at the level of 0.2-0.5%; canonical harmonics 5-7 at the level of 0.8-1.2%; harmonics 11-13 at the level of 1.0-1.2%, respectively; while the coefficient of non-sinusoidal voltage (Kнс) was in the range of 4.5-8.7%.

So, the following values were recorded: n = 22 - 0.9%; n = 25 - 1.3%; n = 29 - 4.6%; n= 36 - 1.8%; n=39 - 1.8%. As can see, there are mostly here even and odd non-canonical harmonics. The appearance of even and odd harmonics of high order in the spectrum can be explained mainly by the asymmetry of the thyristor switching pulses. Oscillography of impulses control thyristors of transducers, performed on ten stands rough and finishing rolling, showed that the permissible rate was 3 e. deg. exceeded in 8 cases and was within e = 5.2-9.5 e. deg.

Considerable research in this direction has been made by prof. I. V. Zhezhelenko. These publications recommend that the harmonics up to the 13th order be taken into account when calculating the quality of electricity. However, our research shows that in this case the calculations of non-sinusoidal coefficients will have an error of 30-40%. Therefore, we offer similar calculations to perform with harmonics up to the 40th inclusive.

The next question, which is solved in the paper, is the definition of the structure of Kнс current and voltage. By the structure of the coefficients, we understand the composition and level of the harmonics that form the indicated coefficients. The statistical method of correlations was used as a research method. Between Kнс and the range of connection is low (phase A - R0 = 0,250; phase B - R0 = 0,227; phase C - R0 = 0,137) despite the fact that the arrays obtained by synchronous oscillography were processed.

In order to analyze the internal structure of the Kнс, the decomposition of random functions into a Fourier series was carried out. The method made it possible to determine the composition and level of harmonics of random processes with subsequent discarding of statistically insignificant coefficients (that is harmonics) by the Student's criterion.

Analysis of the calculations showed that current are formed by odd harmonics of low order n£7; the Kнс of the voltage have a mixed structure, with the main contribution being made by high-order harmonics of n = 21¸ 40, both even and odd.

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DOI: https://doi.org/10.31319/2519-2884.35.2019.47

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ISSN (print) 2519-2884

ISSN (online) 2617-8389