The utility model discloses a monitoring devices is gone into to dc bus alternating voltage of transformer substation cluster for the dc bus monitoring facilities who solves each producer reforms transform or the substitute mode difference, leads to the replacement cost with high, long problem of time spent. The device includes: the alternating voltage module of sampling, CPU control module and report an emergency and ask for help or increased vigilance the module in proper order the order connect, alternating voltage sampling module includes separating straight circuit, voltage sampling circuit, voltage follower circuit, a rectification circuit, filter circuit and AD converting circuit order in proper order connect, AD converting circuit's output is connected with CPU control module's input, it includes blocking capacitance to separate straight circuit, blocking capacitance establishes ties in the dc bus rear end of awaiting measuring, voltage sampling circuit includes voltage transformer, voltage transformer establishes ties in separating straight circuit rear end, an exchange cluster income voltage and sample for treating in the survey dc bus. Above -mentioned device can exchange the monitoring warning of string income to the dc bus.