According to the investigation, occasionally during testing, the programmable AC power supply will have twice the voltage, which is most likely due to the testing machine terminals and input phase connections (U, V, W) before installing or removing the programmable AC power supply cable in a fixed state without reversing. This is called a "phase rotation". When the voltage signal of the U phase is used to drive the V phase, the V phase will advance 120 ° even if the U phase is 0V, resulting in a state where the drive is near full load voltage.

500kW load bank
 

That is, in a three-phase input programmable AC power supply, if the relationship between the input wiring and the thyristor (thyristor) that controls the phase does not match the gate pulse that drives the thyristor, the phase control does not move linearly and may rise to full load voltage as the power is turned on, or the phase control works in reverse when trying to obtain the rated power. This leads to the problem of insufficient power.

Many companies ignore this when connecting the power cord to the trial machine, and then when the test restarts, they are suddenly faced with a 2x voltage situation. Careless care can destroy the test product and cause loss. If the problem is not found after reassembly, but the goods are delivered directly to the customer, it will have a serious impact on the customer. Therefore, the assembly of a programmable AC power supply must pay attention to the "phase rotation" of this input.