Detecting short circuit to earth in pulse inverter - using square wave HF voltage source in evaluation circuit to operate protection circuit when toroidal transformer saturates

摘要

A pulse inverter is fed from a DC source across two DC lines which are led through a toroidal transformer, such that in normal operation the sum of the flow is zero. The sec. winding of the transformer is connected across an evaluation circuit provided with an AC source, with a protective circuit for the pulse inverter. A HF square wave voltage source (U) is used as the AC voltage source in the evaluation circuit (A), which by a saturation of the toroidal transformer (RK) with an earth, is short circuited across a resistor (R3). A current (I1) driven by the square voltage source (U) produces a voltage drop (U3) at the resistor (R3), which activates a signal (ERD OK) for operating the protective circuit (S). ADVANTAGE - Small as possible toroidal transformer, esp. ferrite unit, can be used as earth leakage transformer, for potential separated earth leakage protection for pulse inverter.