DE1036999B - Three-phase conductor system, especially for electric arc furnaces - Google Patents

Description

GERMAN

The invention relates to a three-phase conductor system, in particular for arc furnaces, including in addition to High current line also the electrodes should be understood as parts of the system.

In large three-phase electric arc furnaces - especially with currents over 20,000 A - it is evident during operation that one of the two outer electrodes has a higher arc voltage with the same current strength, the other has a lower arc voltage. The consequence of this is unequal power outputs among these electrodes and greater wear and tear on the Masonry in the area of the so-called sharp phase. This fact is known and has been described several times been. Various measures have been proposed below to eliminate the dead and sharp phase among other things, the arrangement of a compensation transformer between the two outer phases. All of these procedures but fail because of the effort or construction difficulties,

The object on which the invention is based consists of a three-phase conductor system,
especially for electric arc furnaces

Applicant:

Demag-Elektrometallurgie G. mb H.,
Duisburg, Wolfgang-Reuter-Platz

From the equations for the self-inductances Lr, s and Lt it can be seen that in the example given, the effects of the asymmetry due to different dead phases is phase R , in the inductance of the, for example, in one plane, an ohmic resistance due to the asymmetry is added. The sharp phase

is the phase T in which an ohmic resistance of the same size is subtracted.

The knowledge that leads to the solution of the task consists in finding the right-hand sides of the two equations for the self-inductances Lr (dead phase) and Lt

Three-phase current conductors, in particular the two outer three-phase current conductors designated as dead or sharp phase, especially in the case of electric arc furnaces, in a structurally simple and economical manner.

According to the basic equations of the self-inductances of an asymmetrical three-phase system arranged in one plane, the self-inductances of the phase conductors R, S, T arranged according to Fig. 1 are shown as follows:

to equate (sharp phase):

2,. ] / 3 ". _. Dp .] / 3
- +; J- 1η2 = 1η-ϊ; -L

In

In 2

•In 2

and from that the relationship

In X _n = j ·] / 3 · In 2 + In X ₃₃

to develop. This relationship says that the mean 3.Ί geometric distance X _{n of} the cross-section of the dead phase R must be greater than the mean geometric distance X _{33 of} the cross-section of the sharp phase 5, if the inductions in these two outer phases in the sense of a reduction or a compensation of

These equations apply to influences of asymmetry adjusted to one another in one plane

should be.

The inventive teaching for technical action is that in a three-phase conductor system is the mean geometric distance of the cross-section of the

.1 / 3

.in 2

gg
arranged round or rectangular conductors with a center-to-center distance ei from each other. X ₁₁ , x,

'22'

are the middle ones

geometric distances of the cross-sections of the head of the
Phase R or 5 or T of itself. This term
is common in electrical engineering and represents a pure 45 two outer phase conductor different from itself

Calculated variable that has a decisive influence on the self-induction of the conductor and on the size and shape of the Conductor cross-section is dependent.

For a conductor with a circular cross-section, the mean geometric distance is

XKr = 0.77880 r and for a rectangle

xr = 0.2235 (a 4- b).

is chosen large; and the middle one must be geometrical The distance of the (previous) dead phase must be greater than that of the (previous) sharp phase. Ideally, the equation

In X _n = j ·] / 3 · In 2 - \ - In X ₃₃

met.

Since the mean geometric distance of the cross-section of a conductor depends on the cross-section itself,

809 598/252

a three-phase current conductor system according to the invention is characterized externally - if three individual homogeneous, in one level next to each other arranged conductors are used - by different cross-sections of the two outer phase conductors. This is in the drawing in Fig. 1 and 2 for rectangular and tubular conductor cross-sections illustrated. It is possible to apply the principle on which the invention is based to the electrodes continue the arc furnace, d. H. To use electrodes with two different cross-sections. A However, satisfactory results are achieved if the electrodes are left with the same thickness. One the triangular arrangement of the electrodes would bring about further symmetry.

In practice, flexible ropes are used as bundle conductors for parts of the high-current line in electric arc furnaces for each phase, consisting of groups of individual conductors. For such bundle conductors is the concept of the middle geometric distance is not common. As an equivalent, however, one can use the inner self-induction of a Use bundle conductors, which are known to depend on the effective distance between the individual conductors. In order to reduce or compensate for the effects of asymmetry for such a bundle conductor system, According to the further invention, the individual conductors of the one outer phase will have a different effective distance from one another given as the single conductors of the other outer phase; and the distances in The bundle conductor of the previous dead phase must be larger. With the same number of individual conductors, their density is greater the bundle cross-section different. In this way, there is an extensive alignment of the to achieve absolute resistance.

It is most effective to change the effective conductor spacing in the vertical, as shown in Fig. 3 of the drawing. In the drawing, R is always the previous dead phase and T the previous sharp phase.

The individual conductors of the bundle according to Fig. 3 are usually connected by multiple clamps arranged at intervals fixed in their position. According to the invention it is also proposed to prepare these multiple terminals so that the conductor spacing can be changed during operation, which is not special in terms of construction Makes trouble.

Claims (6)

Patent claims: 1. Three-phase conductor system, especially for arc furnaces, to reduce or compensate for the effects of asymmetry as a result of various Inductance of the three-phase conductors lying in one plane, for example, in particular of the two outer, three-phase current conductor designated as dead or sharp phase, characterized in that in the two outer phases of the mean geometric distance of the cross-section of the conductor from itself different is chosen large. 2. Three-phase conductor system according to claim 1, characterized in that the mean geometric distance the (previous) so-called dead phase is larger than that of the (previous) so-called sharp phase. 3. Three-phase conductor system according to claims 1 and 2, characterized in that the mean geometric distance of the cross-section of the two outer phase conductors R and T [X ₁₁ , X ₃₃ ) is so different that the relationship in the case of conductors lying in one plane In X ₁₁ = j · | / 3 · In 2 + In X ₃₃ fulfilled and thus the inductive resistance of the two outer phase conductors is balanced. 4. Three-phase conductor system according to claims 1 to 3 in the form of bundle conductors for each phase, consisting from groups of individual conductors, characterized in that the individual conductors of the one outer Phase have a different effective distance from one another than the individual conductors of the other outer phase. 5. Three-phase conductor system according to claim 4, characterized in that with bundle conductors with predominantly individual ladders arranged one below the other, the effective vertical spacing of the individual ladders are different in phases (Fig. 3). 6. Three-phase conductor system according to claims 2 and 3 with multiple terminals for determining the mutual position of the individual conductors, characterized in that the multiple terminals for changing the conductor spacing is set up during operation. 1 sheet of drawings