This procedure will show if the welding transformer has a short circuit between the windings or the primary and secondary side.
Issue
Checking the welding transformer specifications
- Transformer transformation ratio
- No-load current (A1)
- Insulation measurement
Remedy
Measuring setup diagram:
(Transformer installed in the machine)
Observe regulation on working in low-voltage area. (Electric shock)
- Completely isolate transformer from the converter connection.
- Push insulation between the roller heads, e.g. cardboard.
- Remove welding wire.
If the check is carried out with a Variac and at mains frequency 50Hz, then U primary (V1)
can be calculated using the following formula.
Max.transformer voltage and transformer frequency: see welding transformer type plate.
Example Test voltage result (Uprimary)
Max. transformer voltage: 400V
Transformer frequency: 500Hz
Test frequency: 50Hz Uprimary = 400V x50Hz / 500Hz = 40V (V1)
Transformer transformation ratio
The ratio of voltage V1 to voltage V2 gives the transformation ratio.
(Quotient ÜT = Uprim / Usec)
No-load current (A1)
The size of the no-load current for a good welding transformer is approx. 1.5 …2.5A (AC).
Currents greater than 2.5A indicate an interwinding fault.
Insulation measurement
The purpose of the insulation measurement is to ensure that there is no interwinding fault
between the primary winding and the transformer core.
This measurement should preferably be performed with an insulation tester (up to 1200V).
(Insulation tester: previously also known as "Megger").
- Completely isolate both primary connections from the above arrangement (see diagram).
- Connect insulation tester from a primary connecting cable to the core.
- The ohm reading must be >1MOhm, and the voltage must not be interrupted.