A power system, comprising: a DC channel connected to a high-voltage direct current , abbreviation HVDC, bus ; an HVDC bus ground fault protection device connected to the HVDC bus; and a DC channel ground fault protection device connected to the DC channel, wherein the HVDC bus ground fault protection device is operatively connected with the DC channel ground protection fault device through the DC channel and is configured to cause the DC channel ground fault protection device to disconnect the DC channel from the HVDC bus based on detection of current leakage in the HVDC bus by using the HVDC bus ground fault protection device and then detection of current imbalance in the DC channel by using the DC channel ground fault protection device; and characterised in that the DC channel ground fault protection device includes a common mode current sensor sensitive to current imbalance coupled to the DC channel, and wherein the DC channel ground fault protection device further includes: an amplifier connected to the common mode current sensor; a synchronous detector connected to the amplifier; a comparator connected to the synchronous detector and a channel reference voltage lead; and wherein the comparator is configured to output a disconnect signal based on a comparison of the voltage corresponding current imbalance in the DC channel and a reference voltage received through the channel reference voltage lead. a DC channel connected to a high-voltage direct current , abbreviation HVDC, bus ; an HVDC bus ground fault protection device connected to the HVDC bus; and a DC channel ground fault protection device connected to the DC channel, wherein the HVDC bus ground fault protection device is operatively connected with the DC channel ground protection fault device through the DC channel and is configured to cause the DC channel ground fault protection device to disconnect the DC channel from the HVDC bus based on detection of current leakage in the HVDC bus by using the HVDC bus ground fault protection device and then detection of current imbalance in the DC channel by using the DC channel ground fault protection device; and characterised in that the DC channel ground fault protection device includes a common mode current sensor sensitive to current imbalance coupled to the DC channel, and wherein the DC channel ground fault protection device further includes: an amplifier connected to the common mode current sensor; a synchronous detector connected to the amplifier; a comparator connected to the synchronous detector and a channel reference voltage lead; and wherein the comparator is configured to output a disconnect signal based on a comparison of the voltage corresponding current imbalance in the DC channel and a reference voltage received through the channel reference voltage lead. an amplifier connected to the common mode current sensor; a synchronous detector connected to the amplifier; a comparator connected to the synchronous detector and a channel reference voltage lead; and wherein the comparator is configured to output a disconnect signal based on a comparison of the voltage corresponding current imbalance in the DC channel and a reference voltage received through the channel reference voltage lead. <EOS>