When adding a leakage protection switch in front of the APC UPS power supply device, although there is no leakage phenomenon in the UPS, it is impossible to produce zero similarity due to the magnetic flux vector formed by high-order harmonics in the iron core and the hysteresis effect of the iron core. Leakage artifacts cause frequent tripping of the leakage protection switch. Therefore, leakage protection switches cannot be installed on the AC input of APC UPS power supply.
When the mains power is normal, the rectifier of the APC UPS power supply charges the battery and provides working DC voltage for the frequency converter. When the mains power is cut off, the battery pack provides DC working voltage to the inverter and outputs standard AC power.
When working in online mode, UPS directly rectifies the AC input power supply. Without power factor compensation, it will cause serious harmonics in the transmission line.
During normal operation, leakage current will not pass through the leakage protection switch circuit except for the operating current. At this point, the amplitude of the current flowing through the zero sequence transformer (detection transformer) is equal, the direction is opposite, and the sum is zero. The magnetic flux in the iron core of the induction transformer. It is also equal to zero, the secondary winding has no output, the automatic switch remains conductive, and the leakage protector works normally. When the protected electrical appliances and circuits experience leakage or electric shock, there is a ground fault current that causes the current flowing through the detection transformer to be non-zero. Magnetic flux is induced in the transformer core, and the secondary winding has already induced current. After generation, the amplified output triggers the leakage release action, pushing the automatic switch to trip, achieving the purpose of leakage protection.