IEC07000189 V1 EN-USFigure 56: Earth fault in Direct earthed system7.3.2.6 Settings for Two step residual overvoltage protection M13853-21 v12Operation:Off orOnUBase (given inGlobalBaseSel) is used as voltage reference for the voltage. The voltage can befed to the IED in different ways:1. The IED is fed from a normal voltage transformer group where the residual voltage iscalculated internally from the phase-to-earth voltages within the protection. The settingof the analog input is given asUBase=Uph-ph.2. The IED is fed from a broken delta connection normal voltage transformer group. In anopen delta connection the protection is fed by the voltage 3U0 (single input). The Settingchapter in the application manual explains how the analog input needs to be set.3. The IED is fed from a single voltage transformer connected to the neutral point of a powertransformer in the power system. In this connection the protection is fed by the voltageUN=U0 (single input). The Setting chapter in the application manual explains how theanalog input needs to be set. ROV2PTOV will measure the residual voltage correspondingnominal phase-to-earth voltage for a high impedance earthed system. The measurementwill be based on the neutral voltage displacement.The below described setting parameters are identical for the two steps (n = step 1 and 2).Therefore the setting parameters are described only once.Characteristicn: Selected inverse time characteristic for stepn. This parameter gives the typeof time delay to be used. The setting can be,Definite time orInverse curve A orInverse curve BorInverse curve C orProg. inv. curve. The choice is highly dependent of the protectionapplication.Un>: Set operate overvoltage operation value for stepn, given as % of residual voltagecorresponding toUBase:Section 7 1MRK 505 355-UEN AVoltage protection126Application manual