The function has a high measuring accuracy and a settable hysteresis to allow applications
to control reactive load.
In many cases, UV2PTUV (27) is a useful function in circuits for local or remote
automation processes in the power system.
10.1.3 Setting guidelines
All the voltage conditions in the system where UV2PTUV (27) performs its functions
should be considered. The same also applies to the associated equipment, its voltage and
time characteristic.
There is a very wide application area where general undervoltage functions are used. All
voltage-related settings are made as a percentage of the global base value VBase, which
normally is set to the primary rated voltage level (phase-to-phase) of the power system or
the high voltage equipment under consideration.
The trip time setting for UV2PTUV (27) is normally not critical, since there must be
enough time available for the main protection to clear short circuits and ground faults.
Some applications and related setting guidelines for the voltage level are described in the
following sections.
10.1.3.1 Equipment protection, such as for motors and generators
The setting must be below the lowest occurring "normal" voltage and above the lowest
acceptable voltage for the equipment.
10.1.3.2 Disconnected equipment detection
The setting must be below the lowest occurring "normal" voltage and above the highest
occurring voltage, caused by inductive or capacitive coupling, when the equipment is
disconnected.
10.1.3.3 Power supply quality
The setting must be below the lowest occurring "normal" voltage and above the lowest
acceptable voltage, due to regulation, good practice or other agreements.
10.1.3.4 Voltage instability mitigation
This setting is very much dependent on the power system characteristics, and thorough
studies have to be made to find the suitable levels.
Section 10 1MRK 506 369-UUS -
Voltage protection
568 Line distance protection REL670 2.2 ANSI
Application manual
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