To provide a plant for sending electric power through a DC voltage network for a high-voltage direct current(HVDC) which a voids overmodulation.

In a plant for sending electric power through a station 2 between a DC voltage network 1 and an AC voltage network 4, an apparatus 14 compares a reference AC voltage with a DC voltage between two poles of the DC voltage network on the DC voltage side of the station. When a quotient obtained by dividing the reference AC voltage by one-half of the DC voltage exceeds a previously determined value, a signal is sent to a control equipment contained in the station. When the control equipment receives the signal, it is understood to be a command for increasing the consumption of reactive power on the AC voltage side of the station, so as to control a converter 6 on the basis of the command.