RU2834854C1 - Method of determining power losses from non-sinusoidal currents in three-phase power lines at the same phase load - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering, in particular to determination of power losses from non-sinusoidal currents in electric power transmission systems. At the same phase load, the effective values of harmonic currents in the phase conductor are measured, total losses of active power ΔP in three-phase power transmission line. Criterion for calculating losses from non-sinusoidal currents in line K_ωΔPL based on resistances of direct and zero sequence of three-phase line, effective values of currents of harmonics in phase, including effective value of current of direct component. Determining power losses in a three-phase power transmission line from non-sinusoidal currents by formula ΔP_ω=K_ωΔPL⋅ΔP.

EFFECT: development of a simple method for determining power losses from non-sinusoidal currents in three-phase power transmission lines at the same phase load.

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Description

The invention relates to the field of electrical engineering, in particular to determining power losses in electrical energy transmission systems.

It is known that power losses in three-phase power lines depend, among other things, on non-sinusoidal currents. Such currents arise due to non-linear load when harmonic voltage is applied to it. It is proposed to calculate additional losses from such currents through pulsation powers, distortions, and latent power [R. Drechsler "Measuring and assessing the quality of electric power under asymmetrical and non-linear load": Translation from Czech, Moscow: Energoatomizdat, 1985. - 112 p.].

The disadvantages of these methods of calculating power losses are high labor intensity, computational complexity, and a large volume of measured information.

The closest in technical essence to the declared method is the “Method for measuring power losses from non-sinusoidal currents in three-phase transformers and four-wire power transmission lines” [RU 2638904, G01R 31/06], which consists of measuring, under a non-linear load in a three-phase transformer or four-wire line, the effective value of the harmonic current, the total coefficient of odd and even harmonics, except for harmonics multiples of three, and the total coefficient of harmonics multiples of three, and, based on the measurement results, determining the coefficient of power losses from non-sinusoidal currents using the formula:

The disadvantage of this method is the low sensitivity of the developed coefficient of power losses from non-sinusoidal currents at low values of the fundamental frequency harmonic current compared to the effective values of the higher harmonic currents, that is, at significant non-sinusoidality of the phase current, due to the tendency of the numerical value of this coefficient, in this case, to infinity.

The objective of the invention is to simplify the determination of power losses in three-phase power transmission lines based on the results of measurements of such electrical energy quantities as the effective values of harmonic currents, as well as the power emitted on the power transmission line under study.

The task is solved by measuring the effective values of harmonic currents in the phase conductor, the losses of active power in a three-phase power transmission line, and, based on the measurement results, determining the power losses in a three-phase power transmission line from non-sinusoidal currents using the formula:

where K _{ω ΔPL} is the criterion for calculating losses from non-sinusoidal currents in the line;

R ₁ , R ₀ - resistances of direct and zero sequence of a three-phase line, respectively;

I ₍₀₎ - effective value of the direct current component;

I _{(3 ⋅ n )} - the effective value of the current of harmonics multiples of three;

I _{( n )} - the effective value of the current of the n-th harmonic;

taking into account the criterion for calculating losses from non-sinusoidal currents in the line and the measured losses of active power, the power losses from non-sinusoidal currents in the power transmission line are determined using the formula:

ΔP _ω = K _{ω Δ PL} ⋅ΔP,

where ΔP _ω is the power loss from non-sinusoidal currents in a three-phase power transmission line with the same phase load;

ΔP - total active power losses in a three-phase power transmission line with the same phase load.

New essential features:

1. With the same phase load, the effective values of harmonic currents in the phase conductor and active power losses in a three-phase power transmission line are measured.

2. Based on the measurement results, the criterion for calculating losses from non-sinusoidal currents in the line is calculated using the formula:

3. The criterion for calculating losses from non-sinusoidal currents in the line and the measured active power losses allow us to calculate power losses from non-sinusoidal currents in the power transmission line using the formula

ΔP _ω = K _{ω Δ PL} ⋅ΔP.

The listed new essential features, in combination with the known ones, make it possible to obtain a technical result in all cases covered by the scope of legal protection.

Technical result

The technical result consists in developing a simple method for determining power losses from non-sinusoidal currents in three-phase power transmission lines. With significant non-sinusoidality of the phase current, this coefficient accurately reflects the amount of additional losses from the non-linear load.

Implementation of the method

In modern electrical networks, along with active and reactive loads, there are also nonlinear loads. Such loads cause periodic non-sinusoidal currents, which are a source of additional losses in power transmission lines. When developing means and methods for reducing losses in electrical networks, it is necessary to have information, including on the amount of losses from non-sinusoidal currents.

If in a three-phase network with the same phase load we obtain an image of the current curve in the phase conductor, for example, using an oscilloscope or the Energomonitor 3.3T1 device, then this curve will differ from the sinusoidal signal the more the higher harmonics contribute to its formation.

By measuring, for example, the “Energomonitor 3.3T1” device, the effective values of each harmonic of the current and knowing the resistances of the direct and reverse sequence of the line, it is possible to calculate the criterion for calculating losses from non-sinusoidal currents in the line K _ωΔPL .

To determine losses from non-sinusoidal currents, it is necessary to know the total losses of active power ΔP in an element of the electrical network, which can be calculated from the difference in readings of the Energomonitor 3.3T1 devices connected at the beginning and end of the power transmission line.

Knowing the active power losses and the criterion for calculating losses from non-sinusoidal currents in the line K _ωΔPL, the losses from non-sinusoidal currents are calculated: ΔP _ω =K _ωΔPL ⋅ΔP.

Claims (10)

A method for determining power losses from non-sinusoidal currents in three-phase power transmission lines with the same phase load, including the measurement of electric power quantities, characterized in that, knowing the resistances of the direct and zero sequence of a three-phase line with the same phase load, the effective values of harmonic currents in the phase conductor, the losses of active power in the three-phase power transmission line are measured and, based on the results of the measurements, the criterion for calculating losses from non-sinusoidal currents in the line is calculated using the formula: where K _ωΔPL is the criterion for calculating losses from non-sinusoidal currents in the line; R ₁ , R ₀ - resistances of direct and zero sequence of a three-phase line, respectively; I(0) - effective value of the direct current component; I(3⋅n) - effective value of harmonic current, multiples of three; I(n) is the effective value of the current of the n-th harmonic; taking into account the criterion for calculating losses from non-sinusoidal currents in the line and the measured losses of active power, the power losses from non-sinusoidal currents in the power transmission line are determined using the formula: where ΔP _ω is the power loss from non-sinusoidal currents in a three-phase power transmission line with the same phase load; ΔР - total losses of active power in a three-phase power transmission line with the same phase load.