CN103969497A - Method for measuring arc current of alternating-current electric-arc furnace - Google Patents

Abstract

The invention relates to a method for measuring the arc current of an alternating-current electric-arc furnace and belongs to the technical field of alternating-current electric-arc furnace detection. The method includes the following steps that first, three magnetic field intensity measuring probes following electrodes of all phases in the axial direction are symmetrically arranged around the electric-arc furnace, each magnetic field intensity measuring probe is responsible for tracking and measuring the arc current on the electrode of one phase, and the magnetic field intensity of a certain point in a plane away from the top end of the corresponding electrode for 2 cm to 2.5 cm is measured; second, a magnetic field intensity matrix expression H=1/2phi*M*I generated by the three phases of arc current on the three following points is written down according to the Ampere circuital theorem; third, the matrix expression is transformed into the form that I=2phi*M<-1>*H for representing an arc current matrix through a magnetic field intensity matrix on the three following points; fourth, the effective values of the magnetic field intensity measured by the following magnetic field measuring probes are substituted into the arc current matrix expression in the third step, and then the effective value of the three-phase arc current is obtained. Through the method, the arc current for smelting electrically-smelted magnesium oxide can be accurately measured.

Description

A kind of method of measuring ac arc furnace arc current

Technical field

The present invention relates to measure the method for ac arc furnace arc current, belong to ac arc furnace detection technique field.

Background technology

Ac arc furnace, by the electric arc of discharge generation between electrode and furnace charge, makes electric energy in arc light, change heat energy into, heats and melt the device of metal and slag by the direct effect of radiation and electric arc.The electric current of each phase electrode of flowing through divides two parts, and a part is the arc current of discharge generation between electrode and furnace charge, and another part is the non-arc current flowing through between electrode.The uniform and stable of three-phase arc current is the necessary condition that maintains three electric arc smooth combustions on electrode, the magnitude of current of the current control strategy collection for electric arc furnace smelting is all the electric current that flows through electrode, it is the summation of the non-arc current between arc current and electrode, so just cannot accurately control the size of arc current, can not effectively hold whole smelting process.Therefore how can effectively measure arc current, thereby replace and flow through electric current on the each phase electrode foundation as control electrode lifting with arc current, be in prior art, to have problem to be solved.

Summary of the invention

The object of the invention is provides a kind of method of measuring ac arc furnace arc current for above-mentioned problems of the prior art.

Another innovative point of the present invention is the layout that has designed magnetic field intensity measuring sonde and three-phase electrode, make magnetic field intensity measuring sonde, can be servo-actuated, i.e. the shift in position of accurate tracking electrode in the vertical direction, records apart from the magnetic field intensity on 2～2.5cm place, electrode bottom surface level.

The object of the invention is to be achieved through the following technical solutions:

A method of measuring ac arc furnace arc current, is characterized in that: comprise the steps:

(1) around electric arc furnaces, be arranged symmetrically with 3 groups along each phase electrode axis to servo-actuated magnetic field intensity measuring sonde, every group of magnetic field intensity measuring sonde is responsible for the arc current on tracking measurement one phase electrode, measures apart from certain any the magnetic field intensity in 2cm-2.5cm place, counter electrode top plane;

(2) write according to Ampère circuital theorem row the magnetic field intensity matrix expression being produced by three-phase arc current on three servo-actuated points wherein H is 3 × 1 magnetic field intensity effective value matrix, and M is 3 × 3 matrix of coefficients, and I is 3 × 1 arc current effective value matrix;

(3) matrix expression is transformed into the form I=2 π .M by the magnetic field intensity matrix representation arc current matrix on three servo-actuated points ^-1.H, matrix M wherein ^-1it is the inverse matrix of matrix M;

(4) the magnetic field intensity effective value servo-actuated magnetic field intensity measuring sonde being recorded is brought the arc current matrix expression in step (3) into, obtains the effective value of three-phase arc current.

Described magnetic field intensity measuring sonde end is connected to signal wire, magnetic field intensity measuring sonde connects with corresponding electrode end by fixed pulley group, the end of described fixed pulley group is connected with plummet, and magnetic field intensity measuring sonde is synchronized with the movement with electrode under the traction of vertical.

Beneficial effect of the present invention: the present invention adopts technique scheme, in conjunction with the know-why feature of electric furnace arc current, is parallel to electrode in the space distribution of arc current, and the magnetic field of generation is perpendicular to electrode; The space distribution of non-arc current is perpendicular to electrode, and the magnetic field of generation is parallel to electrode.Therefore can be by measuring the size of calculating arc current perpendicular to the magnetic field of electrode.For example, for the smelting of electrically molten magnesia, utilize the method can accurately measure arc current contribute to control three-phase electric arc evenly and smooth combustion sticks together melting of electric-melting magnesium to be evenly distributed symmetry, the product magnesium content of the electrically molten magnesia of output is high.And the electrical connection that utilizes magnetic field indirectly to measure arc current needn't to transform original electric arc furnaces, convenient installation, does not affect production.Whether the magnetic field environment that can also be used for on-line monitoring scene is simultaneously harmful, reminds workman to take necessary electromagnetic protection measure.

Brief description of the drawings

Fig. 1 is surrounding's three-phase magnetic field intensity measuring sonde of electric arc furnaces and the figure of the location layout of respective electrode.

Fig. 2 is the magnetic field intensity vector plot that magnetic field intensity measuring sonde records.

Fig. 3 is the concrete annexation schematic diagram of a certain magnetic field intensity measuring sonde and electric arc furnaces counter electrode.

Embodiment

A kind of method of measuring ac arc furnace arc current the present invention relates to, its step is as follows:

(1) around electric arc furnaces, be arranged symmetrically with 3 groups along each phase electrode axis to servo-actuated magnetic field intensity measuring sonde, every group of magnetic field intensity measuring sonde is responsible for the arc current on tracking measurement one phase electrode, measures apart from certain any the magnetic field intensity in 2cm-2.5cm place, counter electrode top plane;

(2) write according to Ampère circuital theorem row the magnetic field intensity matrix expression being produced by three-phase arc current on three servo-actuated points wherein H is 3 × 1 magnetic field intensity effective value matrix, and M is 3 × 3 matrix of coefficients, and I is 3 × 1 arc current effective value matrix;

(3) matrix expression is transformed into the form I=2 π .M by the magnetic field intensity matrix representation arc current matrix on three servo-actuated points ^-1.H, matrix M wherein ^-1it is the inverse matrix of matrix M;

(4) the magnetic field intensity effective value servo-actuated magnetic field intensity measuring sonde being recorded is brought the arc current matrix expression in step (3) into, obtains the effective value of three-phase arc current.

Taking a certain group of magnetic field intensity measuring sonde and respective electrode as example, the annexation of the two as shown in Figure 3, the mechanism that has omitted the intrinsic lifting electrode of the electric arc furnaces such as conductive cross arm and electrode card in Fig. 3, in Fig. 3,01 is electrode, 02 is electric arc, 03 is molten bath, 04 is furnace shell, and 05 is signal wire, and 06 is magnetic field intensity probe, 07 is fixed pulley group, and 08 is vertical.

Be connected to the magnetic field intensity probe 06 of signal wire 05, be connected with electrode 01 by fixed pulley group as shown in Figure 3, under the traction of vertical 08, be synchronized with the movement with electrode 01, the effect of signal wire 05 is that the magnetic field intensity signal collecting is delivered to the effective value that carries out abovementioned steps (1) in computing machine and draw to the matrix operation of (4) three-phase arc current.

The concrete servo-actuated principle of servo-actuated magnetic field intensity probe is: in the time that electrode moves upward, vertical drives the identical height that declines of the rope on fixed pulley, and the magnetic field intensity probe connecting with vertical by a fixed pulley can the identical height of rising; In the time that electrode declines, electrode can drive the vertical identical height that rises by fixed pulley group, the magnetic field intensity probe of the vertical opposite side identical height that can decline.

The present invention program's specific design process and theoretical derivation reference are as follows:

In order to realize technical scheme of the present invention, first need according to each phase electrode position, be arranged symmetrically with 3 groups along each phase electrode axis to servo-actuated magnetic field intensity measuring sonde, 3 groups of servo-actuated probe apparatus of electrode are arranged in to the furnace shell center of circle to the extended line of electrode cross-section circle center line connecting, as shown in Figure 1.In Fig. 1,01A is A phase electrode, and 01B is B phase electrode, and 01C is C phase electrode, and 04 is furnace shell, and 06A is the magnetic field intensity probe that A phase electrode pair is answered, and 06B is the magnetic field intensity probe that B phase electrode pair is answered, and 06C is the magnetic field intensity probe that C phase electrode pair is answered.

With reference to Fig. 2, servo-actuated probe summit is designated as to R to the distance on counter electrode axis, servo-actuated probe summit is designated as to D to the distance on all the other two electrode axis, servo-actuated probe summit is designated as to θ to the vertical line on counter electrode axis with the angle of the vertical line to other electrode axis.

In alternating electromagnetic field, the complex vector located form of describing the Ampère circuital theorem of magnetic field intensity and current relationship is expressed as follows

It is magnetic field intensity loop integral along closed-loop path l equals conduction current density and displacement current density integration on the curved surface S surrounding at closed-loop path l.

Because the electrode of electric arc furnaces is by conductor and electric arc conduction, displacement current density in the time burning compare conduction current density negligible.Have

Release according to the power on symmetry in the raw magnetic field of miscarriage of each electrode again

H.2 π r=I (3) H represents the effective value of electromagnetic intensity, and I represents the effective value of electric current, and r representative produces the horizontal range of the servo-actuated probe of electrode axis linear distance in magnetic field, gets R or D, as shown in Figure 2.

According to the superposition principle of vector, the magnetic field intensity that the servo-actuated probe of A phase electrode records probe with A phase electrode connecting line vertical direction on horizontal component equal the magnetic field intensity that the electric current on A phase electrode produces on the corresponding servo-actuated probe of A add the magnetic field intensity that B phase electrode produces on the servo-actuated probe of A phase electrode ? component in direction adds the magnetic field intensity that C phase electrode produces on the servo-actuated probe of A phase electrode ? component in direction.Being write as the scalar form representing with the effective value of magnetic field intensity is

H ₁=H ₁₁+ cos θ .H ₂₁+ cos θ .H ₃₁(4) magnetic field intensity that in like manner, the servo-actuated probe of B phase electrode records probe with B phase electrode connecting line vertical direction on horizontal component equal the magnetic field intensity that the electric current on B phase electrode produces on the corresponding servo-actuated probe of B add the magnetic field intensity that A phase electrode produces on the servo-actuated probe of B phase electrode ? component in direction adds the magnetic field intensity that C phase electrode produces on the servo-actuated probe of B phase electrode ? component in direction.Being write as the scalar form representing with the effective value of magnetic field intensity is

H ₂=H ₂₂+ cos θ .H ₁₂+ cos θ .H ₃₂(5) magnetic field intensity that the servo-actuated probe of C phase electrode records probe with C phase electrode connecting line vertical direction on horizontal component equal the magnetic field intensity that the electric current on C phase electrode produces on the corresponding servo-actuated probe of C add the magnetic field intensity that A phase electrode produces on the servo-actuated probe of C phase electrode ? component in direction adds the magnetic field intensity that C phase electrode produces on the servo-actuated probe of B phase electrode ? component in direction.Being write as the scalar form representing with the effective value of magnetic field intensity is

H ₃＝H ₃₃+cosθ.H ₁₃+cosθ.H ₂₃(6)

Release according to formula (3)

$H=\frac{1}{2\mathrm{\&pi;r}}---\left(7\right)$

With reference to Fig. 2, for H ₁₁, H ₂₂, H ₃₃the magnetic field being produced by the counter electrode of popping one's head in accordingly, corresponding r gets R, and remaining is not the magnetic field being produced by probe counter electrode, and r gets D.Again by the effective value of corresponding electric current on each phase electrode, I ₁, I ₂, I ₃represent respectively A, B, C three-phase voltage, bring formula (4), (5), (6) into and draw

$H_1=\frac{I_1}{2\mathrm{\&pi;R}}+\cos \mathrm{\&theta;}\&CenterDot;\frac{I_2}{2\mathrm{\&pi;D}}+\cos \mathrm{\&theta;}\&CenterDot;\frac{I_3}{2\mathrm{\&pi;D}}---\left(8\right)$

$H_2=\cos \mathrm{\&theta;}\&CenterDot;\frac{I_1}{2\mathrm{\&pi;D}}+\frac{I_2}{2\mathrm{\&pi;R}}+\cos \mathrm{\&theta;}\&CenterDot;\frac{I_3}{2\mathrm{\&pi;D}}---\left(9\right)$

$H_3=\cos \mathrm{\&theta;}\&CenterDot;\frac{I_1}{2\mathrm{\&pi;D}}+\cos \mathrm{\&theta;}\&CenterDot;\frac{I_2}{2\mathrm{\&pi;D}}+\frac{I_3}{2\mathrm{\&pi;R}}---\left(10\right)$

Being write as matrix form is

$\left[\begin{array}{c}{H}_1\\ H_2\\ H_3\end{array}\right]=\frac{1}{2\mathrm{\&pi;}}\&CenterDot;\left[\begin{array}{ccc}\frac{1}{R}& \frac{\cos \mathrm{\&theta;}}{D}& \frac{\cos \mathrm{\&theta;}}{D}\\ \frac{\cos \mathrm{\&theta;}}{D}& \frac{1}{R}& \frac{\cos \mathrm{\&theta;}}{D}\\ \frac{\cos \mathrm{\&theta;}}{D}& \frac{\cos \mathrm{\&theta;}}{D}& \frac{1}{R}\end{array}\right]\&CenterDot;\left[\begin{array}{c}{I}_1\\ I_2\\ I_3\end{array}\right]---\left(11\right)$

Define the matrix M of 3 × 3,

$M=\left[\begin{array}{ccc}\frac{1}{R}& \frac{\cos \mathrm{\&theta;}}{D}& \frac{\cos \mathrm{\&theta;}}{D}\\ \frac{\cos \mathrm{\&theta;}}{D}& \frac{1}{R}& \frac{\cos \mathrm{\&theta;}}{D}\\ \frac{\cos \mathrm{\&theta;}}{D}& \frac{\cos \mathrm{\&theta;}}{D}& \frac{1}{R}\end{array}\right]---\left(12\right)$

Define the matrix H of 3 × 1,

$H=\left[\begin{array}{c}{H}_1\\ H_2\\ H_3\end{array}\right]---\left(13\right)$

Define the matrix I of 3 × 1,

$I=\left[\begin{array}{c}{I}_1\\ I_2\\ I_3\end{array}\right]---\left(14\right)$

Formula (11) can be write as following form

$H=\frac{1}{2\mathrm{\&pi;}}\&CenterDot;M\&CenterDot;I---\left(15\right)$

The value of suitably choosing R makes the determinant of matrix M be not equal to 0, has the inverse matrix M of matrix M ^-1,

2 π M are multiplied by formula (15) both sides ^-1, obtain,

I＝2π.M ^-1.H (16)

Utilize formula (16) just can pass through magnetic field intensity H ₁, H ₂, H ₃try to achieve the arc current I of each phase ₁, I ₂, I ₃.

The concrete application example of technical solution of the present invention: taking the closed electric arc stove of the large capacity of 3000kVA of certain company as example explanation, in this application example, the diameter of stove is 2600mm, electrode diameter is 300mm, centre distance between electrode is 700mm, R gets 1292mm in this example, and calculating D according to geometric relationship is 1930mm, and θ is 11 °.

Have

$M=\left[\begin{array}{ccc}\frac{1}{R}& \frac{\cos \mathrm{\&theta;}}{D}& \frac{\cos \mathrm{\&theta;}}{D}\\ \frac{\cos \mathrm{\&theta;}}{D}& \frac{1}{R}& \frac{\cos \mathrm{\&theta;}}{D}\\ \frac{\cos \mathrm{\&theta;}}{D}& \frac{\cos \mathrm{\&theta;}}{D}& \frac{1}{R}\end{array}\right]=\left[\begin{array}{ccc}{0.774m}^{-1}& {0.509m}^{-1}& {0.509m}^{-1}\\ {0.509m}^{-1}& {0.774m}^{-1}& {0.509m}^{-1}\\ {0.509m}^{-1}& {0.509m}^{-1}& {0.774m}^{-1}\end{array}\right]---\left(17\right)$

$M^{-1}=\left[\begin{array}{ccc}3.026m& -1.229m& -1.229m\\ -1.229m& 3.026m& -1.229m\\ -1.229m& -1.229m& 3.026m\end{array}\right]---\left(18\right)$

Smelt and within latter 6 hours, record three magnetic field intensity effective values on servo-actuated probe and be in blow-on:

H ₁=316A/m, H ₂=300A/m and H ₃=280A/m.The arc current size of trying to achieve each phase according to formula (16) is: I ₁=1528A, I ₂=1101A and I ₃=567A.

Smelt and within latter 8 hours, record three magnetic field intensity effective values on servo-actuated probe and be in blow-on:

H ₁=290A/m, H ₂=260A/m and H ₃=281A/m.The arc current size of trying to achieve each phase according to formula (16) is: I ₁=1335A, I ₂=534A and I ₃=1095A.

Smelt and within latter 10 hours, record three magnetic field intensity effective values on servo-actuated probe and be in blow-on:

H ₁=276A/m, H ₂=278A/m and H ₃=282A/m.The arc current size of trying to achieve each phase according to formula (16) is: I ₁=923A, I ₂=976A and I ₃=1083A.

Claims (2)

1. a method of measuring ac arc furnace arc current, is characterized in that: comprise the steps:

(1) around electric arc furnaces, be arranged symmetrically with 3 groups along each phase electrode axis to servo-actuated magnetic field intensity measuring sonde, every group of magnetic field intensity measuring sonde is responsible for the arc current on tracking measurement one phase electrode, measures apart from certain any the magnetic field intensity in 2cm-2.5cm place, counter electrode top plane;

(2) write according to Ampère circuital theorem row the magnetic field intensity matrix expression being produced by three-phase arc current on three servo-actuated points wherein H is 3 × 1 magnetic field intensity effective value matrix, and M is 3 × 3 matrix of coefficients, and I is 3 × 1 arc current effective value matrix;

(3) matrix expression is transformed into the form I=2 π .M by the magnetic field intensity matrix representation arc current matrix on three servo-actuated points ^-1.H, matrix M wherein ^-1it is the inverse matrix of matrix M;

(4) the magnetic field intensity effective value servo-actuated magnetic field intensity measuring sonde being recorded is brought the arc current matrix expression in step (3) into, obtains the effective value of three-phase arc current.

2. a kind of method of measuring ac arc furnace arc current according to claim 1, it is characterized in that: described magnetic field intensity measuring sonde end is connected to signal wire, magnetic field intensity measuring sonde connects with corresponding electrode end by fixed pulley group, the end of described fixed pulley group is connected with plummet, and magnetic field intensity measuring sonde is synchronized with the movement with electrode under the traction of vertical.