Insulation detecting system and method for composite power supply current transformer

The invention discloses an insulation detecting system and an insulation detecting method for a composite power supply current transformer. The insulation detecting system comprises an insulation detecting unit and a discharging circuit, wherein the insulation detecting unit is connected between a standby power supply of a composite power supply and a direct-current bus of the current transformer; the discharging circuit is connected in parallel with the direct-current bus, wherein a first switch is arranged on a branch circuit for connecting the insulation detecting unit and the direct-current bus; the discharging circuit comprises a first resistor and a second resistor which are connected in series; when the first switch is switched off, the insulation detecting unit detects that a positive electrode end equivalent resistor of the standby power supply and the first resistor as well as the negative electrode end equivalent resistor of the standby power supply and the second resistor are in a non-parallel connection state, so that the error report of the insulation detecting unit caused by the fact that the resistance is reduced after the equivalent resistors of the standby power supply are connected with the resistors of the discharging circuit in parallel is prevented. The system and the method can be used for preventing the error report of the insulation detecting unit caused by the fact that the resistance is reduced after the equivalent resistors of the standby power supply are connected with the resistors of the discharging circuit in parallel.