CLICK HERE TO GET INPUT FILE: RaleInput_104

Designing a 12Vdc, 30kAdc Rectifier Transformer

General Information

Technical parameters

 

 

Input voltage  3 x 400/230, star
Transformer output voltages for Udc = 12Vdc 3 x 12.4Vac, star
3 x 12.4Vac, star
Line output current per secondary: (Ia1,Ib1,Ic1,Ia2,Ib2,Ic2) I1  = 5850Arms
I0  = 4980Arms (dc-comp.)
I2  = 2880Arms
I4 = 1590Arms
I5 = 1170Arms
continuous operating mode
Frequency 50Hz
Ambient temperature 40°C
Temperature rise Max. 120°K, insulation class F
°Short-circuit voltage

Ucc  = 4-5%

with drainage choke for optimal current distribution between the rectifier

Steel & Core

 

 

 

 M165 = M6, annealed, strips for alternated stacking
45°, “round” cross section

Creating Input

4 input screens are used to set the input parameters for the designing of a transformer:

  • Winding parameters per limb
  • Core
  • Environment
  • Other parameters

and 3 screens for selection and set up of material :

  • wires
  • steels
  • cores.

Windings parameters per leg

The following rectifier circuit is often used for low voltage & high current output. For a good current distribution between 2 parallel connected rectifiers (with the drainage choke) the relationship Ucc_s1-s2/Ucc is not the criterion of design..
The core cross section and the induction have to be set so that each secondary has only one turn. The form of the legs cross section has to be “round”

Note that the short-circuit voltage of a rectifier transformer is a complex issue reflecting:

  • the commutation operation mode of a group of windings
  • the voltage drop of the dc-output voltage
  • the current distribution between the parallel connected rectifiers

It has to be prescribed by the user of the transformer.

Primary

The primary is created in star connection. The sine wave input voltage (UA,UB,UC) is 230V (230V per winding).

There is no duty cycle operation mode.

The primary will be manufactured with Cu-foil with a layer insulation of 0.100mm.

Note that there is no big difference from an electrical or magnetic point of view (if the distance between the sectors is small) between the winding made by foil with one sector and the winding made by foil with more (2-8) parallel connected sectors. The first and the last sector will be overloaded by a higher eddy & circulated current losses and due to the thermal insulation to the other sectors they will normally be hotter.

ACHTUNG BILD überprüfen.

All the surfaces of the primary are cooled via the cooling channels of 12-20mm . The space between the yoke and the primary windings is 20mm. With the eddy current losses factor (RacRdc) 1.3 shall be limited the number of the parallel connected foils per winding.

Secondary windings

Both secondary windings are created outside each as  ONE TURN FOIL WINDING.

The sine wave output voltage per winding is 12.4V.

The rms current through each winding  is 8774Arms.

The set current harmonics are calculated for the worst case: Ucc= 0 and Ld = ∞:

Also, there is no duty cycle operation mode on the secondary.

With the eddy current losses factor (RacRdc) 1.1 and 1.3 the use of parallel connected foils or bars per windings  shall be limited.

Note that at this point of the design you cannot prescribe the wire or foil (bar) size. You can select only the wire or family or foil (bar) which the program has to use in order to select the suitable wires or foils (bar) for your application.

The secondary winding has only 12 amd 20mm cooling channels.

The space between the yoke and the secondary windings is 20mm.

Core

On this input screen you can :

  • select and manipulate the selected steel M165, 0.35mm (M6, 14mil)
  • set the operating induction (1.55T) and the frequency (50Hz)
  • select the core assembly 7 (45° & 90°)
  • and select the core .

The “round” core cross section was prescribed by the designer for easier winding of the high current foil (bar) windings: The value of the cross section and the induction were set in order to get only one turn per secondary winding.

The window height was optimized for the low eddy current losses with a Cu-bar thickness between 5mm and 6mm.

 

Environment

The cooling medium is air with the ambient temperature  40°C. The cooling surface of the core is increased by using 4 L-brackets on the core.

The impregnation is practically “dry” 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.

 

Other…

The selected criterion of the design is the temperature rise of 100°K for insulation class F and the efficiency >98.5%. The oval space between the first winding and the tube (stomach), all gaps between the insulation, the windings and the varnish fill factor of them, play a very important roll from the thermal point of view.

 

Test Mode

If you are not satisfied with the solution made by the program you can switch into the Test Mode and change your transformer by hand:

  • Turns
  • Wire size
  • Material (Cu or Al)
  • Number parallel connected wires and their order in strand
  • Cooling channels and insulations
  • Margin
  • Steel
  • Technology parameter (impregnation, gaps,…)

and then you can set it under an operation mode changing:

  • Input voltage
  • Frequency
  • Loads and their K-factors
  • Duty cycle of each winding
  • Ambient temperature
  • Air flow

Note that the program will calculate (not select from a data base) the thickness of the foil (bar) for the prescribed temperature rise of 100°K. In order to get an available foil (bar) you have to set the thickness of the foil by hand.

 

Output

Finally (if you click on the link) you obtain 4 printed pages showing the results.

Note:

The secondary windings have the foil size 290mm x (3x5mm parallel).

If you do not like it this way, you can make the secondary winding with 8 parallel connected sectors 35mm x (3x5mm parallel).