RU2241932C1 - Method of power supply to electric arc installations - Google Patents

Abstract

FIELD: metallurgy; methods of power supply to the electric arc installations.

SUBSTANCE: the invention presents a method of power supply to the electric arc installations and is dealt with the field of metallurgy. According to method the power supply is exercised directly with an alternating current of a commercial frequency/ In the capacity of a transducer they use a thyristor or a transistor self-excited inverter, that is switched on at the moments when the electric current passes through zero mark to keep the conducting capacity of plasma of an arch and to form a curve of the electric current with a shift of its fundamental harmonic in direction to decrease a phase shift in relation to the voltage. At use of the invention it allows to upgraded the electric power quality and to increase the electric arc installation power factor.

EFFECT: the invention allows to upgraded the electric power quality and to increase the power factor of the electric arc installation.

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Description

The invention relates to electrical engineering, and in particular to methods of powering electrical installations using an alternating current arc of industrial frequency, in particular, can be used to power arc steelmaking and ore-thermal furnaces, welding plants, and is aimed at increasing their power factor.

There is a method of supplying electric arc installations with three-phase alternating current of industrial frequency, which consists in the fact that an alternating voltage is supplied to the electrodes from a source through a transformer, under which the arcs burn (Ivanov V.S., Sokolov V.I. power supply of industrial enterprises. - M.: Energoatomizdat, 1985, - 236 p.).

The disadvantages of this method are

- significant distortion of the curved currents of the arcs;

- low power factor (0.5 ... 0.7), due to the delay of the main harmonic of the current with non-linear distortions;

- instability of the arc process due to significant deionization of the arc plasma during the passage of current through zero.

A known method of supplying electric arc installations with direct current through the use of rectifiers (Patent No. 2190815 of the Russian Federation, MKI 7 F 27 V 3/08, C 21 C 5/52. Arc steelmaking furnace DC. // BI No. 29 (2), 2002).

The disadvantage of this method is

a significant increase in the generation of higher harmonic components in the supply network, which affects the quality of electric energy, causing a failure of electrical equipment and power supply systems.

Figure 1 shows the characteristic curve of the arc current (1) and the main harmonic of the current (2).

Figure 2 presents the shape of the current when using a source of increased frequency.

The technical result of the claimed method is to reduce the phase shift between the main harmonic of the voltage and current by changing the current-voltage characteristics of the arc in the region of the transition of current through zero.

To achieve a technical result in the method of supplying electric arc installations using a converter, according to the invention, the power is supplied directly by an alternating current of industrial frequency, and the converter, which is used as a thyristor or transistor autonomous inverter, is turned on at the moments when the current passes through zero to maintain the conductivity of the arc plasma and the formation of a current curve with a shift in the fundamental harmonic in the direction of decreasing the phase shift with respect to voltage.

The essence of the method lies in the fact that it is ensured that the conductivity of the arc column near the current crosses through zero by additionally introducing an increased frequency current from the converter, which can be used as a thyristor or transistor autonomous current inverter. The converter is involved at the moments when the industrial frequency current passes through the zero value and is designed to maintain the conducting state of the arc plasma at the required level, therefore its power is many times less than the power of the electric arc installation. The arc current acquires a close to sinusoidal shape, and the delay of the fundamental harmonic caused by nonlinear distortion decreases (Fig. 1).

The power factor in industrial frequency networks is determined by the main harmonics of voltage and current, therefore, the proposed method leads to an increase in the power factor of electric arc installations and the quality of electric energy, as well as to a decrease in the number of failures of electrical equipment and power supply systems in general.

For example, when the electric arc installation is supplied with industrial frequency current at time t ₁ (Fig. 2), the current source is switched on with a frequency several orders of magnitude higher than the industrial one. The inductance of the transformer, through which the electric arc installation is connected to the mains, is proportional to the frequency, so the current from the source of increased frequency will flow mainly through the arc. At the moment of transition of the industrial frequency voltage through a zero value, the current due to the action of this voltage also decreases to zero. Due to the action of an increased frequency current source, current flows through the arc in this time interval, maintaining its temperature and conductivity at a certain level. With increasing voltage of the industrial frequency, the current begins to increase, and at time t _{2 the} additional source can be turned off.

Claims (1)

A method of supplying electric arc installations using a converter, characterized in that the power is supplied directly by an alternating current of industrial frequency, and the converter, which is used as a thyristor or transistor autonomous inverter, is turned on at times when the current passes through zero to maintain the conductivity of the arc plasma and form a current curve with displacement of the fundamental harmonic in the direction of decreasing the phase shift with respect to voltage.

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