Tri-phase welder 400A

What elements were used:

• tri-phase transformer 13,4kW
• 6 diodes 200A
• primary winding 3x5mm
• secondary winding 4x6mm 110V

That kind of transformer (high power) would not start on C25 fuses, therefore a kind of soft start was needed. Some of secondary winding were unwrapped and the rest of them were divided in two parts and connected parallel, what gave 48 square millimeters of winding on each column and a voltage of 28V (on each). The windings were connected on a star and connected to a bridge getting on the output 65V of DC.
Adjustment of welding power was based on a tri-phase driver on the primary winding side. This kind of solution was used, because of a driver with a soft start (U209B) and the diodes mentioned earlier. The adjustment was built on 3xU209B, 3xBTA41-600. The soft start with this configuration worked very well, but the welding couldn't be made, because of the high tension during welding (electrode heated up to red). This transformer is to “rigid”, because the secondary winding is winded on the primary one. The magnetic stream should be dispelled.
In the book “Maszyny elektyczne” (electrical machines) some useful information can be found. The magnetic stream can be dispelled by using a suppressor on the secondary winding (on the AC).
From the left flat (4x6mm), where the winding was produced, three suppressors were made (20 rolls each on 5x4cm cores). And they have been connected to each column.
The current can be adjusted from 40A - 60V (on idling) to 400A – 65 (on idling). While welding, the voltage is from 24 to 28V, depending on the current of welding. An “anti stick” was build (it's useful when welding in low currents). When the electrode is stick, the current is 5A. The adjustment was made by a potentiometer with an additional scaled voltmeter (made on ICL7107).
While testing 10 electrodes (diameter 4) were welded (one after an other) and the welder was only warm – the diodes were more hot, they were about 40 degrees, therefore a fan was used (on 110V) with a thermostat. The thermostat switches off the welder, if the temperature of the diodes exceeds 70 Celsius degrees.
During the burning of holes, clamp meter pointed 600A.

Schema:



On idle: 1A on phase, while welding with an electrode of diameter 3.2 it points 10-12A on phase:



The white is silicon (to handle the vibrations during welding).



The welder weights 120kg.

Link to original thread – Spawarka trójfazowa 400 A