An object is to accurately monitor deterioration of current or future
voltage stability, by dynamically changing a
bus in which current or future
voltage stability deteriorates, in stability monitoring calculation of a power
system. Hence the present invention provides a
voltage stability monitoring device, which monitors
voltage stability of a power
system, including an assumed change
scenario calculation unit which produces a plurality of assumed change scenarios indicating a
scenario of a change that is assumed based on at least one of a
system configuration of the power system and a change of a tide state; a
voltage stability calculation unit which calculates the
voltage stability using the assumed change
scenario; a voltage
stability margin calculation unit which calculates a voltage
stability margin indicating margin degree of the voltage stability, based on the voltage stability; an each scenario severity
ranking calculation unit which selects an assumed change scenario with
high severity of the voltage stability for each assumed change scenario, based on the voltage
stability margin; a vulnerable
bus calculation unit which calculates which of buses in the power system is a vulnerable
bus that decreases voltage stability, based on the assumed change scenario which is selected; and a monitoring location change unit which changes a monitoring target of the voltage stability, based on information of the vulnerable bus.