The power generation which use the mains and generation to supply power must use the mains/genset transfer system, the system can choose automatically the mains or genset to provide the power for the other once necessary. And the principle is as following: When the main power fails to supply the power, the ATS can start the genset right away and indicate the main power failure alarm. The manual transfer switch will be transferred to the genset's power supply position once the genset start, then the genset supply the power accordingly