Auxiliary power supply system for urban rail transit vehicle

The utility model discloses an auxiliary power supply system for an urban rail transit vehicle, which comprises a train power supply bus (1), an auxiliary power supply (2) and an isolation three-phase AC contactor (3). One auxiliary power supply (2) is mounted in each carriage of a train; the auxiliary power supply and the power supply bus form a parallel network to load and supply power for the train; and the isolation three-phase AC contactor (3) is mounted on the power supply bus (1) at least. The contactor (3) is in the closed state when the system is in the normal running state; and a switch controlling device is arranged in the auxiliary power supply (2). Therefore, the contactor is switched off if the grounding of the train bus or the short-circuit fault are detected; and the other auxiliary power supplies can normally supply power. Likewise, if any one auxiliary power supply is in fault, the switch controlling device in the auxiliary power supply is switched off to realize isolation between the auxiliary power supply and the train power supply bus, thereby achieving the purpose of improvement of the train operation reliability.