Performance of welding transformers

An important component in resistance welding is the welding transformer. This was described in principle in Episode 8. The decisive factor in resistance welding is the performance behaviour. Welding transformers are operated near the short circuit with a relatively low duty cycle. The nominal power is determined according to ISO (DIN) for 50 % ED (duty cycle) with an integration time of one minute. The decisive factor here is the thermal capacity of the transformer. A welding transformer is thus constructed in such a way that a very high power can be output for a short duty cycle without it being thermally overloaded.

The power at the required duty cycle can be calculated from the nominal power. For example, a welding transformer with a rated power of 100 kVA can deliver 224 kVA at a duty cycle of 10 %. The calculation can be obtained from your welding technology partner or you can find the formula in the corresponding DVS leaflets or also in the book “Resistance Pressure Welding” by Manfred Krause, DVS Volume 25.

The transformer manufacturers usually also provide the corresponding performance diagrams in the documentation. The welding machines are again specified with a defined short-circuit power. Due to the secondary impedance of the machine, this is always smaller than the short-circuit power of the welding transformer. These power specifications, which are relevant for the welding application, can be found in the power specifications of the corresponding machines.