The power fluctuation test is generally used to confirm whether various instruments using programmable AC power are operating incorrectly.

 

500kW load bank
 

The fluctuation test of programmable AC power supply includes short-term interruption, voltage drop, harmonic application test and other tests. Especially in the use of transformers in the built-in power supply equipment, or the use of boost transformer and other equipment in the line test equipment for short-term interruption test, under certain setting conditions, the transformer may form a large current (programmable AC power overload, can not be successfully tested). The following describes the causes of overcurrent formation and the setting conditions to avoid overcurrent formation.

An overcurrent waveform generated by a short interruption of a programmable AC power supply. As can be seen from the figure, although the short-term interruption in (a) has ended, the overcurrent shown in (B) will be generated when the next negative side sine wave arrives.

The reason is that the magnetic saturation of the transformer occurs at the time point (B). That is, if the programmable AC power supply has no short interruption of (a), the magnetic flux of the transformer will reset through the positive string peak, but due to the power outage, the magnetic flux is not reset, forming a state of negative side magnetic flux.

Therefore, when the next negative side of the positive string peak arrives, the magnetic flux of the programmable AC power supply is more negative, exceeding the saturation magnetic flux density, and finally the excitation inductance basically becomes zero. As the inductance disappears, the overcurrent shown in (B) occurs.

Thereafter, the current and voltage fluctuations of the programmable AC power supply occurred. This is because the current limit Protection (OCP) of AC power supplies sometimes imposes current limits and sometimes does not, so there are fluctuations.