which is normally set to the nominal voltage level (phase-to-phase) of the powersystem or the high voltage equipment under consideration.The time delay for the OV2PTOV can sometimes be critical and related to the sizeof the overvoltage - a power system or a high voltage component can withstandsmaller overvoltages for some time, but in case of large overvoltages the relatedequipment should be disconnected more rapidly.Some applications and related setting guidelines for the voltage level are givenbelow:The hysteresis is for overvoltage functions very important to prevent that atransient voltage over set level is not “sealed-in” due to a high hysteresis. Typicalvalues should be ≤ 0.5%.9.2.3.1 Equipment protection, such as for motors, generators, reactors andtransformers M13852-10 v3High voltage will cause overexcitation of the core and deteriorate the windinginsulation. The setting has to be well above the highest occurring "normal" voltageand well below the highest acceptable voltage for the equipment.9.2.3.2 Equipment protection, capacitors M13852-13 v1High voltage will deteriorate the dielectricum and the insulation. The setting has tobe well above the highest occurring "normal" voltage and well below the highestacceptable voltage for the capacitor.9.2.3.3 Power supply quality M13852-16 v1The setting has to be well above the highest occurring "normal" voltage and belowthe highest acceptable voltage, due to regulation, good practice or otheragreements.9.2.3.4 High impedance earthed systems M13852-19 v6In high impedance earthed systems, earth-faults cause a voltage increase in thenon-faulty phases. Two step overvoltage protection (OV2PTOV) is used to detectsuch faults. The setting must be above the highest occurring "normal" voltage andbelow the lowest occurring voltage during faults. A metallic single-phase earth-fault causes the non-faulted phase voltages to increase a factor of √3.9.2.3.5 The following settings can be done for the two step overvoltageprotection M13852-22 v10ConnType: Sets whether the measurement shall be phase-to-earth fundamentalvalue, phase-to-phase fundamental value, phase-to-earth RMS value or phase-to-phase RMS value.Section 9 1MRK 505 393-UEN BVoltage protection194 Line differential protection RED650 2.2 IECApplication manual
