Insulation detector and electric apparatus

An insulation detector connected between one of a P bus and an N bus of an electric apparatus and an output line, the electric apparatus including a rectifier circuit that is disposed between an alternating-current power supply and a load and converts an alternating-current voltage from the alternating-current power supply into a direct-current voltage and an inverter that is connected to a post stage of the rectifier circuit and drives the load, and the output line connecting the inverter and the load, wherein

• the insulation detector comprises a series-connected measurement resistor and a voltage-dividing resistor, a capacitor connected in parallel to a circuit consisting of the series-connected measurement resistor and the voltage-dividing resistor, and a voltage detector configured to detect a plurality of voltage values across the measurement resistor, wherein the plurality of voltage values includes a first voltage value, a second voltage value and a third voltage value measured across the measurement resistor respectively at a first time, a second time and a third time,
• the insulation detector is configured to detect an insulation resistance between the load and a ground or a housing based on the plurality of voltage values across the measurement resistor, and
• the insulation detector is configured to estimate a value of the insulation resistance according to a relationship among the first voltage value, the second voltage value and the third voltage value measured across the measurement resistor respectively at the first time, the second time and the third time.