RU2644454C2 - Method for measuring power losses from nonsinusoidal currents in three-phase transformers and four-wire power transmission lines - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method of measuring power losses from reactive currents in three-phase transformers and four-wire lines is that the power factor (cos) is measured with a symmetrical linear load in a three-phase transformer (four-wire line)ϕ,phase current and from the measurement results determine the power loss factor from reactive currents by the formula.

EFFECT: ability to determine individual power losses from reactive currents in three-phase transformers and four-wire power lines, a minimum set of material and technical means.

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Description

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

It is known that power and energy losses in three-phase transformers and power lines depend on the reactive currents in them. In the book of R. Drechsler “Measurement and assessment of the quality of electric power under asymmetric and non-linear load”: Translation from Czech, M .: Energoatomizdat, 1985. - 112 p. It is proposed to evaluate the losses in the elements of the power transmission system by the magnitude of the ripple power, latent power, distortion power, and reactive power.

According to these indicators, a large amount of measurement information with rather cumbersome further calculations will be required to measure losses.

The closest technical solution to the invention is the "Method for measuring losses and idling current of power transformers in the field and a device for its implementation" (RF Patent No. 2533530, IPC G01R 31/06, published on November 20, 2014), which provides for measuring the voltage on the primary transformer winding with open secondary winding. In this method of measuring the losses of power transformers, an autonomous asynchronous generator with field capacitors is used as a source of controlled voltage, the output voltage of which is stepwise regulated within the range from 70 to 110% of the nominal voltage by switching the regulation capacitors when the switching voltage passes through "zero" by three-phase contactless electronic keys controlled via optocoupler inputs with a decoder and multi-position switch eat.

The disadvantage of this method is the measurement of total losses in the transformer at idle, and not the individual components of the power losses from reactive currents, as well as the inability to measure losses in the transformer in operating mode.

The objective of the invention is the determination of power losses from reactive currents in three-phase transformers and four-wire power lines according to the results of measurements of known indicators of electricity:

- power factor for the first harmonic cosϕ.

The problem is solved as follows.

In a method for measuring power losses from reactive currents in three-phase transformers and four-wire lines, using a regulated three-phase voltage source, a power factor (cosϕ) is measured at a symmetric linear load in a three-phase transformer (four-wire line), the phase current and the power loss coefficient are determined from the measurement results from reactive currents according to the formula

, откуда ΔP_x=K_ϕΔP_R,

, whence ΔP _x = K _ϕ ΔP _R ,

where ΔP _x - power loss from reactive currents;

- потери активной мощности.

- loss of active power.

New significant features

1. The power factor (cosϕ) of a three-phase transformer (line) and the phase current I _{f are} measured in a four-wire network with a symmetric linear load and cosϕ <1.0

2. The measurement results determine the coefficient of power loss from reactive currents in a three-phase transformer (line) according to the formula

определяют потери мощности от реактивных токов в трансформаторе (линии)3. Knowing the coefficient K _ϕ and the loss of active power

determine the power loss from reactive currents in the transformer (line)

ΔP _x = K _ϕ ΔP _R.

The listed new essential features, together with the known ones, are necessary and sufficient to achieve a technical result, to which an exhaustive scope of legal protection applies.

Technical result

1. A simple method has been developed for measuring power losses from reactive currents in three-phase transformers and four-wire lines, which constitute additional losses, due to the reduction of which the overall losses are reduced.

2. The minimum set of material and technical means.

3. Measurements are carried out with the help of one measuring device “Energy Monitor 3.3” of high accuracy class 0.1, the reduced error of which does not exceed 0.1%. Therefore, the accuracy of measuring the power factor (cosϕ) will be high (there is no methodological error).

4. The developed mathematical expression for the coefficient of power loss from reactive currents in three-phase transformers and four-wire lines is simple. Therefore, there are no cumbersome calculations of power losses in three-phase transformers and four-wire lines.

Explanation of the method of measuring losses

Modern three-phase four-wire networks, as a rule, have a reactive load. Therefore, reactive currents are created in them. In three-phase transformers and four-wire lines, power and electric energy losses from reactive currents occur. When developing tools and methods for reducing losses in transformers and lines, it is important to have information not only about total losses, but, first of all, about partial power losses that make up these losses and take measures to reduce them. Partial losses include power losses from reactive currents.

In a three-phase four-wire network with a symmetric sinusoidal three-phase voltage system and a symmetric linear load at cosϕ <1.0, a symmetric sinusoidal current system with a phase angle ϕ arises. In such a network, active P _R and reactive P _x power are transmitted from the source to the receiver. In a three-phase transformer and a four-wire line, active ΔP _R and reactive ΔP _x power losses occur. Having measured the power factor (cosϕ) and phase current I _{f of the} transformer (line) with the Energy Monitor 3.3 instrument, the criterion (coefficient) of power losses from reactive currents is determined, which is equal to the ratio of reactive power losses to active power losses

Where

Knowing the loss of active power and the coefficient Kϕ, determine the power loss from reactive currents

ΔP _x = K _ϕ ΔP _R

The source of information

1. Drechsler R. Measurement and assessment of the quality of electricity under asymmetric and non-linear load: Translation from Czech M .: Energoatomizdat, 1985. - 112 p.

2. RF patent No. 1533530. A method for measuring losses and idling current of power transformers in the field and a device for its implementation. IPC G01R 31/06, published on November 20, 2014.

Claims (4)

A method for measuring power losses from reactive currents in three-phase transformers and four-wire lines, which involves the use of a regulated three-phase voltage source, characterized in that the power factor (cosϕ) is measured at a symmetric linear load in a three-phase transformer (four-wire line), and the phase current is determined from the measurement results coefficient of power losses from reactive currents according to the formula

whence ΔP _x = K _ϕ ΔP _R , where ΔP _x - power loss from reactive currents;

- loss of active power.