APPARATUS FOR DETECTING EARTH LEAKAGE CURRENT OF INVERTER IN INDUCTION MOTOR THROUGH THREE CURRENT DETECTING RESISTANCES

摘要

PURPOSE: An apparatus is provided to protect the inverter of an induction motor from an earth leakage current by using three current detecting resistances for detecting an earth leakage current. CONSTITUTION: An apparatus comprises a power unit(11) for applying a three-phase current voltage; a rectifying and smoothing unit(12) for converting the three-phase current voltage into a rectified and smoothed DC voltage; an inverter unit(13) for receiving the DC voltage output from the rectifying and smoothing unit, switching the applied voltage by a command signal, and outputting a three-phase AC voltage; an induction motor(14) operating by the three-phase AC voltage of the inverter unit; first to third current detecting resistances(Rs1 to Rs3) for detecting an earth leakage current when a command signal is applied to the inverter unit, and detecting, through resistances, the current in accordance with the switching state of the inverter unit when the induction motor is in operation by the inverter unit; and a ground resistance(Rg) for grounding the earth leakage current which flows when an earth leakage current is generated from the output side of the inverter unit.