2.3 APPLICATION NOTES
2.3.1 UNDERVOLTAGE SETTING GUIDELINES
In most applications, undervoltage protection is not required to operate during system earth fault conditions. If this
is the case y
ou should select phase-to-phase voltage measurement, as this quantity is less affected by single-
phase voltage dips due to earth faults.
The voltage threshold setting for the undervoltage protection should be set at some value below the voltage
excursions that may be expected under normal system operating conditions. This threshold is dependent on the
system in question but typical healthy system voltage excursions may be in the order of 10% of nominal value.
The same applies to the time setting. The required time delay is dependent on the time for which the system is able
to withstand a reduced voltage.
If motor loads are connected, then a typical time setting may be in the order of 0.5 seconds.
Stage 1 is used for tripping and can be disabled, or selected as IDMT or DT. You can set stage 2 as an alarm stage
to warn the user of unusual voltage conditions.
If only a single-phase VT signal is available and you require an undervoltage alarm, you must set the VTS status
signal in the SUPERVISION column to Indication or disabled.
Chapter 11 - Voltage Protection Functions P64x
240 P64x-TM-EN-1.3
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