1. High Current, Low Voltage: Resistance welding utilizes resistance heat as its heat source. Because the resistance is very low (generally less than 100μΩ), a sufficiently high current is required to generate the necessary heat. Common welding currents range from 2000 to 40000A.
Since the resistance of both the workpiece and the welding circuit is in the micro-ohm range, the secondary voltage of the transformer is not high. Fixed welding machines typically operate below 10V, while suspended welding machines, due to their longer and wider welding circuits, reach approximately 24V.
Because resistance welding requires high welding current and low voltage, the secondary winding of the transformer used for resistance welding only uses one turn (two turns for suspended or long-arm welding machines). Therefore, the conductor size of the welding circuit in resistance welding machines is relatively large, and forced cooling is required.
2. High Power, Adjustable: Due to the high welding current, the capacity of resistance welding transformers is greater than 50kVA. Since the transformer winding has only one or two turns, the welding power can only be changed by altering the number of turns in the primary winding.
3. Discontinuous Operation, No No-Load Operation: Generally, the switch of a resistance welding transformer is placed between the primary winding and the power supply line. Before connecting the primary winding to the network, the workpiece is already clamped within it, and the welding circuit is closed. Once the power is turned on, the transformer operates under load, so there is generally no no-load state (except for flash butt welding). During welding, the procedures of workpiece loading and unloading, clamping, welding position movement, and pre-pressing, forging, and resting in the welding cycle generally do not require power connection. Therefore, the energized working time of the resistance welding transformer is intermittent.