10.3.3 Setting guidelinesAll the voltage conditions in the system where ROV2PTOV (59N) performs its functionsshould be considered. The same also applies to the associated equipment, its voltagewithstand capability and time characteristic.All voltage-related settings are made as a percentage of a settable base voltage, whichshall be set to the primary nominal voltage (phase-phase) level of the power system or thehigh-voltage equipment under consideration.The time delay for ROV2PTOV (59N) is seldom critical, since residual voltage is relatedto ground faults in a high-impedance grounded system, and enough time must normally begiven for the primary protection to clear the fault. In some more specific situations, wherethe residual overvoltage protection is used to protect some specific equipment, the timedelay is shorter.Some applications and related setting guidelines for the residual voltage level are givenbelow.10.3.3.1 Equipment protection, such as for motors, generators, reactors andtransformersEquipment protection for transformersHigh residual voltage indicates ground fault in the system, perhaps in the component towhich two step residual overvoltage protection (ROV2PTOV, 59N) is connected. Forselectivity reasons to the primary protection for the faulted device, ROV2PTOV (59N)must trip the component with some time delay. The setting must be above the highestoccurring "normal" residual voltage and below the highest acceptable residual voltage forthe equipment.10.3.3.2 Equipment protection, capacitorsHigh voltage will deteriorate the dielectric and the insulation. Two step residualovervoltage protection (ROV2PTOV, 59N) has to be connected to a neutral or open deltawinding. The setting must be above the highest occurring "normal" residual voltage andbelow the highest acceptable residual voltage for the capacitor.10.3.3.3 Power supply qualityThe setting must be above the highest occurring "normal" residual voltage and below thehighest acceptable residual voltage, due to regulation, good practice or other agreements.Section 10 1MRK 506 369-UUS -Voltage protection576 Line distance protection REL670 2.2 ANSIApplication manual
