How to calculate the power of a welding machine
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How is the power of a welding machine calculated? My method of multiplying the welding current by the welding voltage doesn’t give the correct result, and when I use the input voltage, I don’t know the input current. Please advise those who are knowledgeable. I’m a beginner student and don’t know where to post this. Please forgive me if I’ve posted it in the wrong place.
The nameplate indicates the apparent power of the welding machine, such as 10KVA and so on. Since a welding machine is not a purely resistive circuit but includes electromagnetic coils, there is not only active power but also reactive power. Knowing the apparent power and the power factor, it is possible to calculate the active power.
Note: Welding machines have a special parameter called the load factor, which refers to the frequency of use of the device. It’s difficult to provide a specific figure for a single unit. Multiple units can be used to calculate statistics! :Lol, as far as I remember, the light load factor for ordinary welding machines is around 0.35; in other words, when the motor operates at full load, it’s similar to the simultaneous factor used in load calculations. Last edited by ZJYSSF on 2009-3-14 23:26.]
To determine the no-load current of a 380V single-phase welding transformer without a nameplate: to find its rated capacity, use the formula: rated capacity in kVA = no-load current multiplied by five. A single-phase AC welding transformer is essentially a step-down transformer for special purposes; its basic working principle is roughly the same as that of ordinary transformers. To meet the requirements of the welding process, the welding transformer operates in a short-circuit condition, and it is necessary to have a certain arc-starting voltage during welding. As the welding current increases, the output voltage drops sharply; when the voltage drops to zero (that is, when there is a short circuit on the secondary side), the current on the secondary side does not become excessive either. In other words, the welding transformer has a steep voltage-drop characteristic, and this characteristic is achieved thanks to the voltage drop generated by the reactance coil. When unloaded, since no welding current flows through it, the reactance coil does not generate a voltage drop; at this time the unloaded voltage is equal to the secondary voltage. In other words, the behavior of a welding transformer when unloaded is the same as that of an ordinary transformer when unloaded. The no-load current of a transformer is generally around 6% to 8% of the rated current (**it is specified that the no-load current should not exceed 10% of the rated current**). This is the theoretical basis for mnemonics and formulas.
According to the rule stated on floor 4, which says that the no-load current of a welding machine should be 10% or less of its rated current, and that the capacity of the welding machine is equal to the no-load current multiplied by five, if a welding machine has a rated current of 400A, then the calculated rated power would be 400*10%*5 = 200 watts. Yet the apparent power indicated on the machine’s label is 25 kilowatts. Why is there such a big difference? I need to calculate it based on that when getting the cable.
The original poster is correct; the unit for apparent power is not watts or kilowatts, but rather volt-amps (VA) or kilovolt-amps. For example, if a transformer has a capacity of 400 kVA, this refers to its rated capacity.