9.3 Two step residual overvoltage protectionROV2PTOV IP14546-1 v49.3.1 IdentificationSEMOD54295-2 v6Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberTwo step residual overvoltageprotectionROV2PTOV2(U0>)IEC15000108 V1 EN-US59N9.3.2 Application M13809-3 v8Two step residual overvoltage protection ROV2PTOV is primarily used in highimpedance earthed distribution networks, mainly as a backup for the primary earth-fault protection of the feeders and the transformer. To increase the security fordifferent earth-fault related functions, the residual overvoltage signal can be usedas a release signal. The residual voltage can be measured either at the transformerneutral or from a voltage transformer open delta connection. The residual voltagecan also be calculated internally, based on the measurement of the three phase-to-earth voltages.In high impedance earthed systems the residual voltage will increase in case of anyfault connected to earth. Depending on the type of fault and fault resistance theresidual voltage will reach different values. The highest residual voltage, equal tothree times the phase-to-earth voltage, is achieved for a single phase-to-earth fault.The residual voltage increases approximately to the same level in the whole systemand does not provide any guidance in finding the faulted component. Therefore,ROV2PTOV is often used as a backup protection or as a release signal for thefeeder earth-fault protection.9.3.3 Setting guidelines M13853-3 v8All the voltage conditions in the system where ROV2PTOV performs its functionsshould be considered. The same also applies to the associated equipment, itsvoltage withstand capability and time characteristic.All voltage-related settings are made as a percentage of a settable base voltage,which shall be set to the primary nominal voltage (phase-phase) level of the powersystem or the high-voltage equipment under consideration.The time delay for ROV2PTOV is seldom critical, since residual voltage is relatedto earth faults in a high-impedance earthed system, and enough time must normallybe given for the primary protection to clear the fault. In some more specific1MRK 505 393-UEN B Section 9Voltage protectionLine differential protection RED650 2.2 IEC 197Application manual
