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Designing a 3 phase, 50/60Hz rectifier transformer  (YYD) to suppress 5. and 7. current harmonics with 2 parallel connected bridge rectifiers for Udc=400V, Idc=1000A

General Information – Technical Specification

Creating Input

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

• Winding parameters per leg
• 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 to compensate the 5. and 7. current harmonics on the primary side. The parallel connection of the rectifiers is normally used if the output current Id is over 500-1000Adc. For a good current distribution between 2 parallel connected rectifiers (with the chockes Ld1 and Ld2) the relationship Ucc_s1-s2/Ucc has to be bigger than 2; Ucc_s1-s2 is the short-circuit voltage between the secondary 1 and the secondary 2; Ucc is the short-circuit voltage of the transformer. For this condition the primary will be “sandwiched” between both secondaries.

For equal current distribution between 2 parallel connected rectifiers (without the chockes Ld1 and Ld2) the relationship Ucc_s1-s2/Ucc has to be bigger or equal 4.

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

• the rectifier protection in a short circuit operation mode of all secondary winding, a group of windings or of only one winding.
• 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 rectifiers.

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Primary

The primary is created with 2 in series connected windings . The sine wave input voltage (UA,UB,UC)is 400V (400V per winding).

There is no duty cycle operation mode.

The primary will be manufactured with Cu-foil with a layer insulation of 0.1mm.

The primary lies between the secondary windings. All the surfaces of the primary are cooled via the cooling channels of 12mm (inside the core window) and 12mm (outside  the core window). The space between the yoke and the primary windings is 20mm. With the eddy current losses factor (RacRdc) 1.3 shall be limited the foil thickness.

Secondary

The first secondary is connected in delta.

The sine wave output voltage is 314V.

The rms current through each winding (secondary) is 234Arms.  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 will limit  the number f parallel connected foils per winding. Note that at this point of the design you cannot prescribe the wire or foil size. You can select only the wire family or foil which the program has to use in order to select the suitable wires or foils for your application.

The first secondary winding is cooled via the 20mm cooling channels (outside the core window) and via 2mm insulation to the core (inside the core window). The second secondary winding has only two 20mm cooling channels outside the core window. It is winding is better cooled than the first secondary winding.

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

The second secondary is connected in star.
The sine wave output voltage is 182V.
The rms current through each parallel connected winding  should be 205Aac (total output rms curren is 410Aac). 

The set current harmonics are calculated for the worst case: Ucc= 0 and Ld = ∞.
Also, there is no duty cycle operation mode on this secondary.

With the eddy current losses factor (RacRdc) 1.1 the use of the parallel connected foils per winding shall be avoided.

This  secondary winding is cooled via the 12mm cooling channels  (outside the core window) and 12mm (inside the core window). 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, 035mm (M6, 14mil)
• set the operating induction (1.65T) and the frequency (50Hz)
• select the core assembly 7 (mix.45°&90°)
• annealed with 35% remanence

 The oval core cross section was prescribed by the designer. It is  easier. to wind  the high current foil windings: EI3P 750×650/240 oval 2 steps.

Environment

The cooling medium is air with the ambient temperature  40°C.  The cooling factors for the convection 0.8. 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. The oval space between the first winding and the tube (stomach), all gaps between the insulations and  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 for the prescribed temperature rise of 100°K. In order to get an available foil you have to set the thickness of the foil by hand.

ACHTUNG BILD ABGESCHNITTEN!

Output

Finally here are 4 printed pages showing the design results (click on link to see and print PDF).