WO2010027290A1

WO2010027290A1 - Wound delta magnetic core for three phase transformer

Info

Publication number: WO2010027290A1
Application number: PCT/RS2008/000027
Authority: WO
Original assignee: Abs Minel-Trafo, Ad-Joint Stock Company
Priority date: 2008-09-05
Filing date: 2008-09-05
Publication date: 2010-03-11
Also published as: EP2443638A1; RS20080403A; RS51714B

Abstract

One of three identical, rectangular and rounded spools (Fig No. 1) is constructed with seven different steps wound from five different widths of magnetic sheet material. First step is wound rectangular and other steps are wound with shear angle of 30 deg. for every layer of magnetic material. Thickness of wound layer is constructed in such a way that the tops of rectangular and slope steps are placed on a circumcircle and their bottoms are placed on diameter of the same circumcircle. That circumcircle diameter has direction 30 deg. shifted from perpendicular of the spool axis. Three spools are linked accordingly in triangle by fitting of their longer sides (Fig No. 3) and their contact surfaces are fixed with polyglass tape.

Description

Wounded delta magnetic core for three phase transformer

Tehnical Field

This invention refers to three phase transformers manufacture's issues and relates to the way of forming delta type magnetic core from three wound rectangular spools with rounded short sides. Spools are consisted of electrical steel stripes of various widths with shift angle of 30^° for each layer. These three spools are joined to form equilateral triangle in such way that longer sides of spools constitute symmetrical halves of magnetic circuit limbs. According to International Patent Classification signature is

Technical Issues

This invention solves how to form delta core type for three phase transformers..

Background Art

In contemporary three phase transformer manufacturing, the E-core is the most common type of magnetic core which is constructed by stacking of numerous specially cut parts of electrical steel. These parts are of different shapes, typically:

-for yokes, trapezoidal shape with 45° angles and V-cutout of 90° in the middle, -for outside limbs, trapezoidal shape with 45° angles, -for central limb, double arrow shape with vertex of 90°.

The improved method "STEP LAP" additionally has two holes in each electrical steel stripe for technological purposes, to enable proper magnetic core stacking. Three phases of transformer are joined in the same line which cause difference in interphase relations and that will introduce asymmetry of electrical values in power transmission system. Magnetic circuit of such transformer consists of few thousands parts, and cutting waste is above 5%. Once, the stacking of such magnetic circuit is finished the core is still in loosely state and has to be extra fasten by additional means in order to become compact and to reduce the noise during transformer operation.

Three phase delta type of magnetic core has symmetric, natural disposition of the phases in the vertices of equilateral triangle, and its yoke cross-section area is only half of cross-section area of the limb. All three yokes are of the same length, and its total mass is 2/3 mass of yokes for equivalent E-type magnetic core. No-load currents for delta type magnetic cores are symmetric, with identical amplitudes in all three phases and^' they are third harmonic free. In nowadays practice delta type cores are rarely in use due to very complex known method of winding. There is a good attempt of Swedish firm Hexaformer with hexagonal cross-section shape of core, but with insufficient geometric fulfilling of ideal circle, about 82.5%. Wound magnetic cores of any electrical machines compared with cut and stacked ones have many advantages: simple, fast and cheap building process, small magnetizing current, reduced noise level during transformer operation, and possibility of core torrefing which result in reversion to original properties of electrical steel, which are inevitably worsen after every treatment.

Disclosure of Invention

With this invention Delta magnetic core winding is easy to do, fast, and with a minimal decreasing of electric steel properties due to slightly electric steel deformation during spool winding. Three identical rectangular spools with rounded short sides should be wound from electrical steel stripes of various widths with correspondent step with total shift angle of 30 ° , then these three spools should be joined to form delta type core. Connection of the limbs is fasten by wrapping around with polyglass tape. In case that core torrefmg should be performed, spools are connected by metal bands, after process is finished metal bands should be removed and polyglass tape should be applied. smicanja bude 30°, pa se tri kanure spoje u DELTA jezgro. Zatim se tri stuba jezgra obmotaju poliglas trakom i na taj nacin ucvrste kanure medjusobno. Ako se zbog vracanja pocetnih

The advantage of this invention is that any stripe width with 57.7% and less of core circumcircle diameter could be used. Normally, by using optimization, it could be gained a degree of ideal geometrical circle fulfilment above 90% with seven steps (the same with five stripe widths, because some stripes recur in winding).

Brief Description of Drawings

The invention is fully described in winding implementation example on the scheme:

Fig NoI - presents wound spool in two projections. Left projection is spool cross-section on the middle of the spool length.

Fig No2 - presents Δ type core cross-section on the middle of the limbs where the join of three identical spools is shown.

Fig No3 - presents in that way formed Δ type core in three-dimensional picture.

Fig No4 - presents detailed cross-section of n steps spool:

• bi(ai) - depth b of i layer, attained from width a of electrical steel stripe i.

• lengthwise texture presents electrical steel stripe.

• Dj - core circumcircle diameter. Windings are wound on the core.

• 30°- is key angle of layers shift of electrical steel stripes winding.

Detailed Description of The Invention

The pictures show Δ type magnetic core and its three identical spools in general. For each particular case of transformer these should be defined:

Dj- the exact value of core circumcircle diameter

Bj- the exact value of distance between limbs

Hj- the exact value of core limbs straight length

Rj- wanted inner radius of rectangular spool rounding (Fully rounding is shown on pictures and that is why spool lateral side does not have straight part on pictures.)

30°- is unconditional overall angle of spool shifting during winding.

In accordance with pictures displayed, the procedure of spool manufacturing is as follows:

1. Definition of wound layers depth of corresponding stripes width:

This procedure could be done graphically and analytically in respect with picture No4 denotations.

• The spool b₀ (a₀ ) is wound flat (without 30° shift). Grafical definition of stripe

D₁ width a₀ (a₀ < — -) and layer depth b₀ is obvious Analytically b₀ is as follows:

• The first spool M^αi) and _an other spools, is wound with 30° shift. Grafical

D definition of stripe width a_x ( a₀ < a_λ <= — - and its step does not have to, unless in cutoff case, to touch the circumcircle) and depth b_x is obvious. Analytically \ is as follows:

where a₂ is width of second step (^₁ < a₂ < 0.577 D₁ ).

• The other spools b_t(a_t) , 2<=i <=n; the roots of quadratic equation should be checked:

- 2α,tg30° ± ^4α, V30° - 4(l + rg²30°)(α₍ ² - 0.25Z⁾/ )

^{X>m ' ~} 2(i + tg²30°)

If both of them are negative then:

If one of them is positive( X₁₁ ) then b_v = X_n —

• 2. Definition of spool inner width and length (winding pattern):

• Shorter side of spool pattern B: B = B_j - (D_j COSdO⁰ + 2b₀ )

• Longer side of spool pattern B: A = H_j + 2R_}

Wound spools are joined together in a triangle by mating their flat sides (pictures No2 and No3) and connection is fastened by wrapping around with polyglass tape.

Claims

CIaim

1. Wounded delta type magnetic core of three phase transformer consists of three identical spools (Fig NoI), joined by their longer sides in a triangle (Fig No2 and Fig No3) each of them wound of different electrical steel stripes width, characterized by, that winding of all layers (except for first step 137:13 vhich is flat) is done with next layer 30° shifted and that the layers of steps winding are defined (Fig No4) in such a way that their apices circumscribe half of circle end their bases lie on its diametar 30° shifted from normal on winding axis.