Hitachi Relion 670 Series Applications Manual page 190

Section 9
Voltage protection
U2RWPTUV prevents sensitive equipment from running under conditions that could cause
overheating and thus shorten their life time expectancy. In many cases, it is a useful function in
circuits for local or remote automation processes in the power system.
9.1.4 Setting guidelines
All the voltage conditions in the system where U2RWPTUV performs its functions should be
considered. The same also applies to the associated equipment, its voltage and time characteristic.
There are wide applications where general undervoltage functions are used. All voltage related
settings are made as a percentage of the global base value UBase and base current IBase, 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 setting for U2RWPTUV is normally not critical, since there must be enough time available for the
main protection to clear short circuits and earth faults.
Some applications and related setting guidelines for the voltage level are described in the following
sections.
9.1.4.1 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.
9.1.4.2 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.
9.1.4.3 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.
9.1.4.4 Backup protection for power system faults
The setting must be below the lowest occurring "normal" voltage and above the highest occurring
voltage during the fault conditions under consideration.
9.1.4.5 Settings for two step undervoltage protection
Parameters for U2RWPTUV application function are set via local HMI or Protection and Control
Manager PCM600.
Common base IED values for primary current (IBase), primary voltage (UBase) and primary power
(SBase) are set in the global base values for settings function GBASVAL.
GlobalBaseSel: To select GBASVAL function for reference of base values.
ConnType: Sets whether the measurement shall be phase-to-earth fundamental value, phase-to-
phase fundamental value, phase-to-earth RMS value or phase-to-phase RMS value.
Operation: For undervoltage protection Off/On.
UBase (given in GlobalBaseSel): Set as rated phase-to-phase voltage in primary kV. This voltage is
used as reference for voltage setting. U2RWPTUV measures selectively phase-to-earth voltages, or
phase-to-phase voltage chosen by the setting ConnType. The function will operate if the voltage
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