1. Malfunctioning of a voltage regulator or wrong settings under manual control(symmetrical voltage decrease).2. Overload (symmetrical voltage decrease).3. Short circuits, often as phase-to-ground faults (unsymmetrical voltage decrease).UV2PTUV (27) prevents sensitive equipment from running under conditions that couldcause their overheating and thus shorten their life time expectancy. In many cases, it is auseful function in circuits for local or remote automation processes in the power system.7.1.3 Setting guidelinesAll the voltage conditions in the system where UV2PTUV (27) performs its functionsshould be considered. The same also applies to the associated equipment, its voltage andtime characteristic.There is a very wide application area where general undervoltage functions are used. Allvoltage related settings are made as a percentage of the global settings base voltageVBase, which normally is set to the primary rated voltage level (phase-to-phase) of thepower system or the high voltage equipment under consideration.The setting for UV2PTUV (27) is normally not critical, since there must be enough timeavailable for the main protection to clear short circuits andground faults.Some applications and related setting guidelines for the voltage level are described in thefollowing sections.7.1.3.1 Equipment protection, such as for motors and generatorsThe setting must be below the lowest occurring "normal" voltage and above the lowestacceptable voltage for the equipment.7.1.3.2 Disconnected equipment detectionThe setting must be below the lowest occurring "normal" voltage and above the highestoccurring voltage, caused by inductive or capacitive coupling, when the equipment isdisconnected.7.1.3.3 Power supply qualityThe setting must be below the lowest occurring "normal" voltage and above the lowestacceptable voltage, due to regulation, good practice or other agreements.Section 7 1MRK 511 286-UUS AVoltage protection152Application manual
