The microprocessor-controlled static transfer switch constantly monitors the sources connected to the inputs; checks whether they remain within the current and frequency limits and decides if they are synchronized with each other. If the prioritized source is within the determined limits, critical load is transferred over to the prioritized source. If the prioritized source is not within the determined limits, load is then transferred to the other source which is within the determined limits.
https://pmienergy.com/static-transfer-switch/