Static Transfer Switch Function

The function of a static switch: It can only work normally in parallel when the frequency and amplitude of two AC power sources are the same. When a fault occurs in one of the AC power sources, a balanced current will be generated between the two power sources, causing a change in the output voltage of the two parallel power sources and affecting the reliability of the power supply. The function of a static switch is to cut off the faulty power output and achieve uninterrupted switching between the inverter output and the mains bypass output. For online UPS power supplies with a capacity of less than 2kVA, fast relays are mostly used as switching elements for the inverter output and mains bypass output, as their 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 over 2kVA, the switching time will increase to 80ms to 120ms due to the increase in relay operating current. In addition, the sparks generated when the relay breaks will generate high temperatures and damage the contacts, or an arc will form between the normally open and normally closed contacts, causing an instantaneous short circuit between the two AC power supplies. Therefore, the use of relays for switching is limited to small capacity UPS power supplies. The AC dual contactor with interlocking characteristics can control UPS power supplies with high output power, but its switching time is more than ten milliseconds.