Designing a simple 50 kVA, 50Hz three phase dry
transformer with cooling channels?
3 x 400V, star
3 x 230V, delta
Steel & Core
annealed,3 phase EI lamination, alternated stacking
There are 4 input screens to set the input parameters for the designing of
Winding parameters per limb
end 3 screens for selection and set up of material :
In this power range you normally use a 3 phase EI core with grain oriented
steel M111 (M6).
Due to the relative small window width of
this core type there is no enough space for
more than one cooling channel (15mm) between the primary and the secondary.
In order to increase the cooling surface the primary and the secondary are
created with 2 one-sector-windings
with the cooling channels (15mm) between them located
outside of the core window.
Around the core leg is the tube (3mm). There are cooling channels
(15mm) between the first primary winding and the tube located
only outside of the core window. The primary and secondary
windings have the same distance (15mm) to the yokes.
The transformer works in continuous
operating mode on the sine wave input voltage and the sine wave output
The program has to use Cu flat wires with the layer insulation of 0.1mm (100
micron). In a case
program needs to use 2 or more parallel connected
wires the program does not need to use the transposition.
The factor of the eddy current losses (RacRdc = Pcu_total/Pcu_dc) must not
Note that at this point in the design
you can not prescribe the wire size. You can prescribe only the wire family
which the program has to use in order to select the applicable
wires for your application.
On this input screen you can :
manipulate a steel (M111<=>M6)
set the operating induction (1.55T)and the
select the core assembly (EI)
the core selection.
Usung the ollowing
screen for the selection of the core family
the program will pick up the first sufficiently large core for your application out
of the selected core family
LTCM_EI_3_L_1.USR Note that you can also select
or create a new core within this screen
Normally for this application use and M11, 0.35mm (M6,
14mil) grain oriented,
not annealed after stamping, 3 phase EI lamination.
The cooling medium is air with an ambient
The cooling surface of the core is increased by using 4 L-brackets
on the core.
The impregnation is practicallyy
because there is only 10% varnish (90% air) in the windings and in all the gaps between the insulations
and the layers of the windings
The selected criterion of the design is the temperature rise of 100°K for
insulation class F.
The oval space between the first winding and the tube (stomach),
all gaps between the insulations
& windings, and the varnish fill factor play a very
roll from the thermal point of view.
The first step of the design is the selection of the core:
and the next step is the presentation of the output screen
DIAGNOSIS: it is the summery of the most important calculated parameters of
The following 3 screens will not be printed. Note that the program uses the numerical calculation
of the magnetic fields and the temperature rises. Due to this technology the
calculations of the eddy current losses, the steel losses, the short-circuit
voltage, the circulating current and the transposition are very powerful.
Finally, here are 4 printed pages with all the results of
Nominal operating mode
If you are not satisfied
the solution made by the program you can switch into the Test Mode and change
your transformer manually:
Material (Cu or Al)
connected wires and their order in strand
parameter (impregnation, gaps,...)
and then you can set it under an operation mode changing:
Loads and their K-factors
Duty cycle of each winding
Note that the program could not create full layer windings at the
rise of 100°K. In order to get the full layer windings
you have to select the wire size and number in parallel connected
The following Test Mode input shows the operation mode with:
the input voltage on the overvoltage of 10%
the decreased load resistance for 50%
Setting the load resistance to 0 you can simulate the short circuit operation
of the winding.
Setting the load resistance
to >1000 you can simulate the "no-load"
operation of the winding.
the duty cycle operation with 5 minutes on and