Special equipments are available to manufacture the 3D transformer wound core with complete technical support. Both plane wound core and 3D wound core can be realized. http://youtu.be/ndyUy-MqVAo

1. Transformer with
3D wound core

2. Definition (GB25438-2010)
1. Terms and definition
Terms and definition in GB 1094.1, GB/T 2900.15 and below are
applied in this standard.
2. Three dimensional wound core
Core combined by three single wound core frames with the same
size to form a 3D triangle.
3. Distribution transformer with 3D wound core
Distribution transformer with magnetic circuit of 3D wound core

3. Structural analysis and evolution of core
Innovation of core structure
In traditional lamination stacked core with air gap, coupled magnetic
circuit of A-C phase is 1/2 longer than that of A-B and B-C, so the magnetic
circuit is not balance, reluctance of A-C phase is bigger. (See figure 1)
When three-phase voltage is applied to the transformer, three-phase
balanced flux ΦA, φB and φC are generated on the core. When three-
phase balanced flux goes through unbalanced magnetic circuit, magnetic
pressure on phase A and C is big, which affects three-phase voltage
balance. Imbalance on the magnetic loop is a structural defect which
cannot be overcome for transformer with plane core.
Fig. 1 Structure of plane core

4. Plane wound core is without seam, saving weight on 4
corners, which is suitable to single phase transformer.
In 1940s, 500KVA transformer with wound core (shell type) in Moscow transformer
factory.
In 1960s, transformer with single phase wound core was applied in China.
In 1986, the first 30kVA transformer with three-phase closed wound core was
manufactured in Shanghai.
In 1990s, industry equipment and technology were imported from Japan and Sweden to
China, and trial production started.
Plane core
AC intersecting
chain flux
AB intersecting
chain flux
BC intersecting
chain flux
Saving 4 corners
compared to stacked core

5. For symmetry of three-phase
magnetic circuit – It has been…
Yoke
Yoke
Core limb

6. Single frames and combination
Fig. 2 Arrangement of 3D cores and single
frames

7. 
Compared with traditional transformer structure with lamination
stacked core, transformer with 3D wound core is a kind of new and high
performance transformer with more reasonable structure, better
performance and lower producing cost. Great popularization and wide
use of this transformer will greatly save sources of energy and material
with remarkable economic profit. Therefore, this kind of transformer
will catch general attention and interest.

The whole 3D wound core is composed by three identical single frames,
and three core limbs of the combined core are arranged in equilateral
triangle. Each single frame is wound by several ladder shaped material
strips continuously and orderly, and the cross section of wound single
frame is near semicircle, and the combined cross section is quasi-
polygon which is very close to a circle.

Different size of ladder-shaped strips for winding single frame can be
got by suit cut on special curve slitting machine. This kind of suit cut is
without waste material, which is to say the utilization rate of material is
100% during suit cut.

9. Advantages in six aspects
 Saving material and reducing manufacturing cost: 20% silicon steel and 5% wire can be
saved compared with that of plane three-phase lamination stacked core with the same
capacity, thus it obviously reduces manufacturing cost, which is very popular with any
transformer manufacturer and customer.

Improving performance: with the same core and magnetic flux density, no-load loss is
reduced by around 15% compared with that of transformer with plane lamination stacked
core.

Greatly reducing no-load current: no-load current is reduced by 70~80% compared with
that of transformer with plane stacked core.

Reducing noise obviously: 10 decibel is reduced compared with that of transformer with
plane lamination stacked core. (5 decibel reduced for open type)

Improving production efficiency: for open type wound core, core winding and coiling
winding can be carried out at the same time, which improves production efficiency by
more than 50%; reparation is much easier.

Three-phase balance: because of different three-phase magnetic path length, no-load loss
on two side frames of the transformer with plane three-phase stacked core is 20% more
than that on the central column; while no-load loss on three core limbs of the transformer
with three-phase 3 D triangular wound core are the same because of the same magnetic
path length of three core limbs, so three-phase balance is perfect.

10. Advantage
ContinuousContinuous
windingwinding
AnnealingAnnealing
IncreasingIncreasing
magneticmagnetic
performanceperformance
and loweringand lowering
technologytechnology
coefficientcoefficient
Reducing no-Reducing no-
load currentload current
Reducing no-Reducing no-
load lossload loss
SymmetricSymmetric
al layoutal layout
IndependentIndependent
symmetricalsymmetrical
looploop
Three-Three-
phasephase
balancebalance
No three timesNo three times
harmonic waveharmonic wave
FasteningFastening
without airwithout air
gapgap
ReducingReducing
noisenoise
ShortShort
magneticmagnetic
circuitcircuit
ReducingReducing
load lossload loss
High fill factorHigh fill factor
and laminatedand laminated
coefficientcoefficient

11. Advantages
Open type coreOpen type core
winding andwinding and
coil windingcoil winding
can be carriedcan be carried
out at the sameout at the same
time.time.
Easy reparation
ImprovingImproving
efficiencyefficiency
Lessen humanLessen human
factor to havefactor to have
stable qualitystable quality
ManufacturinManufacturin
g of core andg of core and
windingwinding
needs specialneeds special
equipment.equipment.
A little investment on
equipment
It is used forIt is used for
thin materialthin material
processing.processing.
Product withProduct with
highhigh
performanceperformance
and low lossand low loss
SavingSaving
materialmaterial
Small size / light weight, loweringSmall size / light weight, lowering
cost and good looking appearancecost and good looking appearance

12. Slitting machine, Rewinding machine and Winding machine

13. Winding of single frame is on the
special winding machine for 3D
wound core. While winding this
kind of material strips, the
winding machine can
automatically finish a 30 degree
angle with precision on material
to assure the well binding
between surfaces on combining
three single frames.

14. Core winding

15. Alignment of three windows

16. Annealing
under vacuum
During manufacturing of wound core, as silicon steel
experienced transportation, loading and unloading,
slitting and winding process, stress generates on the
cold-rolled silicon steel and then affects its magnetic
performance. To recover its grain orientation and
realize ordered arrangement of the grain inside the
steel and to recover its magnetic performance as
much as it leaves factory, stress shall be removed
under the condition that insulation coating is not
damaged, and the core needs annealing. During
annealing, there is no phase change on silicon steel,
no grain size change or structure change, only
magnetism is recovered. Verified by testing, no-load
loss on the core after annealing is reduced obviously.
Rising time Preserving time Cooling down time
Temperature

17. Annealing under vacuum

Annealing is mostly affected
by annealing equipment,
temperature, time
(temperature rising,
preserving and decreasing),
silicon steel grade, and
quantity put in oven, core
diameter, atmosphere in
oven, which makes
technology coefficient of core
loss with large dispersion.

Annealing consumes large
quantity of power.