| JP3813350 | AMORPHOUS IRON-CORE TRANSFORMER |
| JP57027010 | V-CONNECTION TRANSFORMER |
| JP58225621 | THREE-PHASE WOUND CORE |
| 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. |
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 b 0 (a 0 ) is wound flat (without 30° shift). Grafical definition of stripe
D 1 width a 0 (a 0 < — -) and layer depth b 0 is obvious Analytically b 0 is as follows: • The first spool M α i) and a n other spools, is wound with 30° shift. Grafical
D definition of stripe width a x ( a 0 < 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 a 2 is width of second step (^ 1 < a 2 < 0.577 D 1 ).
• The other spools b t (a t ) , 2<=i <=n; the roots of quadratic equation should be checked:
- 2α,tg30° ± ^4α, V30° - 4(l + rg 2 30°)(α ( 2 - 0.25Z ) / )
X>m ' ~ 2(i + tg 2 30°)
If both of them are negative then:
If one of them is positive( X 11 ) 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 COSdO 0 + 2b 0 )
• 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.
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