ALGORITHM FOR DETERMINING THE NOSINUSOIDALITY COEFFICIENT OF ELECTRICAL QUALITY INDEX FOR WELDING EQUIPMENT

ABSTRACT

In this state description of the quality of electricity, voltage non-sinusoidality, the percentage limit of the non-sinusoidal coefficient at rated voltages, formulas for finding harmonic currents of DC and AC electric arc welding machines. An algorithm has been developed for determining the total coefficient of supply network nonlinearity during the operation of electric arc welding equipment, developed on the basis of the formula.

АННОТАЦИЯ

В данной государственной описания качества электроэнергии, носинусоидальности напряжения, процентный предел коэффициента носинусоидальности при номинальных напряжениях, формулы для нахождения гармонических токов аппаратов электродуговой сварки постоянного и переменного Разработан алгоритм определения суммарного коэффициента нелинейности питающей сети при работе оборудования электродуговой сварки, разработанного на основе формулы.

Keywords: power quality indicators, GOST 13109-97, voltage nosinusoidality, electric arc welding equipment, higher harmonics, algorithm, coeffitsient of nosinusoidality

Ключевые слова: показатели качества электроэнергетики, ГОСТ 13109-97, носинусоидальность напряжения, электродуговой сварки оборудования, высшие гармоники, алгоритм, коэффициент носинусоидальности

As a result of accelerating production processes, improving and introducing new technologies, valve converters, single-phase and three-phase electric welding equipment, high-power electric arc and contact welding equipment, volt-ampere nonlinear loads are increasingly used.. Power transformers, magnetic amplifiers and gas discharge lamps have such features. The feature of these devices is that they consume nosinusoidal currents in the network when a sinusoidal voltage is applied to their terminals.

Nosinusoidal current curves can be considered as complex harmonic oscillations consisting of a set of simple harmonic oscillations of different frequencies. The high harmonic currents flowing through the network elements lead to a voltage drop across the resistance of these elements, which, in addition to the main sinusoidal voltage, distorts the shape of the voltage curve, deteriorating the quality of electricity in the supply network, i.e. an electromagnetic compatibility problem is created with the power supply.

Nosinusoidal voltage is characterized by the following parameters:

• Nosinusoidal distortion coefficient of voltage sinusoid
• The coefficient of the nth harmonic component of the voltage is

The distortion coefficient of the voltage sinusoid is determined by the ratio of the base value of the harmonic composition of the nosinusoidal voltage to the base frequency voltage:

                        (1)

where U_nom- is the voltage value of the nth harmonic; n is the number of the last recorded harmonics.

It is allowed to exclude harmonics with a value of less than 0.1% in the calculation of K_u

The normal allowable and maximum allowable values   of the voltage sinusoidal distortion coefficient in different voltage power grids [2] are given in Table 1 as a percentage.

Table 1

Disruption coefficient of voltage sinusoidality

Permissible values of the coefficient of the nth harmonic component of the voltage at the common connection points to the power grids of different nominal voltage U_nom are given in Table 2 (in percent).

Table 2

Coefficient of n harmonic constituents of voltage

The normal values   given for n = 3 and 9 belong to single-phase networks. In three-phase networks, it is taken as half of the values   given in Table 2.

The allowable limit values   of the n-th harmonic component are 1.5 times higher than those shown in Table 2.

According to their impact on the non-sinusoidal of the supply network, welding loads can be divided into two categories: installations for arc and resistance electric welding of alternating current, installations for electric arc welding of direct current.

AC electric arc welding installations act on the supply network in the same way as arc steel furnaces. Switching on welding machines for contact electric welding is carried out using ignitron or thyristor keys, which, for smooth regulation of the welding current, are equipped with phase control systems for the ignition angle, which leads to distortion of the current by higher harmonics, the level of which is similar to the level of harmonics for AC arc welding.

Figure 1. Algorithm for determining the nosinusoidality coefficient in the network for welding equipment

In the general case, for a single installation of AC electric welding, the harmonic currents (it is recommended to take into account only the third and fifth harmonics [6]) are equal to:

here S_nomТ is the nominal power of the transformer; β_CV is the load factor; PV - duration of inclusion.

The definition of harmonic currents generated by DC electric arc welding installations is similar to the definition of harmonics for valve converters. Harmonic currents (it is recommended to take into account only the 5th, 7th, 11th, 13th harmonics) of a single installation of DC electric arc welding are determined by the formula

where I_SV is the rated primary current of the installation.

For a group of electric welding installations, regardless of the operating mode, the total individual harmonic currents are determined according to [6]

where I_ni is the current of the n-th harmonic of the i- th installation; N is the total number of operating installations.

To assess the impact of welding loads on the enterprise network, the overall coefficient of non-sinusoidal is determined by the formula, %,

Here   voltage of the n-th harmonic.

Algorithms are used to generalize the sequence of technological processes. The following is an algorithm for determining the nosinusoidality coefficient in a network of welding equipment. Based on this algorithm, the sequence of determining the coefficient of nosinusoidality of voltage in a network connected to alternating current and constant current welding devices is expressed.

In this case, according to the initial data, using formulas (2,3,4,5,6) n-3, 5 harmonic currents In for alternating current welding equipment are determined. Determines the harmonic voltages of n-3, 5 under the influence of the welding machine on the mains. To assess the effect of the welding device on the quality of electricity, the total coefficient of nosinusoidality is determined.

When the nominal voltage is kV, when the nosinusoidality coefficient in the power grid is equal to Ku≤8%, the nosinusoidality coefficient in the power grid is normal, if not equal, the filter device in the power grid installation is recommended. When the nominal voltage is , when the nosinusoidality coefficient in the power grid is equal to Ku≤5%, the nosinusoidality coefficient in the power grid is normal, if not equal, the filter device in the power grid installation is recommended. When the nominal voltage is , when the nosinusoidality coefficient in the power grid is equal to Ku≤4%, the nosinusoidality coefficient in the power grid is normal, if not equal, the filter device in the power grid installation is recommended. When the nominal voltage is , when the nosinusoidality coefficient in the power grid is equal to Ku≤2%, the nosinusoidality coefficient in the power grid is normal, if not equal, the filter device in the power grid installation is recommended. When the nominal voltage is U_nom≥220 kV, the voltage is not checked for nosinusoidality coefficient.

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