METHOD FOR IDENTIFYING AN EARTH FAULT IN A RESONANT-EARTHED THREE-PHASE POWER TRANSMISSION SYSTEM, OR A THREE-PHASE POWER TRANSMISSION SYSTEM WHICH IS ISOLATED FROM EARTH POTENTIAL

摘要

The method involves verifying whether interlinked phase voltages of a three-phase power transmission system exceed a predetermined amplitude-based unsymmetric threshold relative to one another by a testing device (20). A symmetric signal is formed, where the symmetric signal indicates symmetric or unsymmetric interlinked phase voltages. The symmetric signal is used for monitoring an earth fault in the power transmission system, where the power transmission system is isolated from earth potential. Independent claims are also included for the following: (1) a safety device comprising a testing device for monitoring an earth fault in a three-phase power transmission system (2) a method for operating an arrangement with two safety devices (3) a method for generating an error signal for a single-phase earth fault.