8.1.3 Setting guidelinesAll the frequency and voltage magnitude conditions in the system where SAPTUF (81)performs its functions should be considered. The same also applies to the associatedequipment, its frequency and time characteristic.There are two specific application areas for SAPTUF (81):1. to protect equipment against damage due to low frequency, such as generators,transformers, and motors. Overexcitation is also related to low frequency2. to protect a power system, or a part of a power system, against breakdown, byshedding load, in generation deficit situations.The under frequency PICKUP value is set in Hz. All voltage magnitude related settingsare made as a percentage of a global base voltage parameter. The UBase value should beset as a primary phase-to-phase value.Some applications and related setting guidelines for the frequency level are given below:Equipment protection, such as for motors and generatorsThe setting has to be well below the lowest occurring "normal" frequency and well abovethe lowest acceptable frequency for the equipment.Power system protection, by load sheddingThe setting has to be below the lowest occurring "normal" frequency and well above thelowest acceptable frequency for power stations, or sensitive loads. The setting level, thenumber of levels and the distance between two levels (in time and/or in frequency)depends very much on the characteristics of the power system under consideration. Thesize of the "largest loss of production" compared to "the size of the power system" is acritical parameter. In large systems, the load shedding can be set at a fairly high frequencylevel, and the time delay is normally not critical. In smaller systems the frequencyPICKUP level has to be set at a lower value, and the time delay must be rather short.8.2 Overfrequency protection SAPTOF (81)Section 8 1MRK 511 286-UUS AFrequency protection166Application manual
