Preventing high contact AC potentials - by monitoring superimposed direct voltage levels using cascaded circuits, for either single or three phase

摘要

The method prevents excessively high contact potentials in alternating and three-phase current networks and involves measuring the isolation resistance by applying a d.c. voltage. When the resulting voltage level exceeds a defined value an optical and/or acoustic alarm or further switching process is activated. The measurement voltage derived from the superimposed d.c. voltage ais decoupled and processed for use by the series isolation monitor warning and indication elements using several different criteria. The associated equipment (1) contains a high impedance choke, a capacitor charged from the network (3) an analyser (6) and indicator (14). Further isolation monitors (2) can be added using connections (15,16) provided. A voltage follower (10) is connected before the analyser (6).