Basic schematic diagram of static switch

The function of the static switch: two AC power supplies can work normally in parallel only when their frequencies and amplitudes are the same. When a certain AC power supply fails, a balanced current will be generated between the two power supplies, causing the output voltage of the two parallel power supplies to change, affecting the reliability of the power supply. The function of the static switch is to cut off the failed power output and achieve uninterrupted switching between the inverter output and the mains bypass output. For online UPS power supplies less than 2kVA, fast relays are mostly used as switching elements to switch between the inverter output and the mains bypass output, because its switching time is only 2ms to 5ms, which is suitable for communication equipment that requires uninterrupted power supply. For UPS power supplies with a capacity of more than 2kVA, due to the increase in the operating current of the relay, the switching time will increase to 80ms ~ 120ms, and the sparks generated at the moment when the relay is disconnected will generate high temperatures and damage the contacts, or the contacts will be damaged when the relay is normally open and normally open. An arc is formed between the normally closed contacts and the two AC power supplies are momentarily short-circuited, so the use of relays for switching is limited to small-capacity UPS power supplies. Although the AC double contactor with interlocking characteristics can control a UPS power supply with a large output power, its switching time is more than ten milliseconds.