GE PACSystems RX3i User Manual page 24

1
ANSI 81U – Under-frequency Protection
ANSI 81O – Over-frequency Protection
1-18
Detection of abnormally low frequency compared to the nominal frequency, to monitor
power supply quality. An alarm will be triggered if a circuit's frequency falls below the
nominal frequency minus the UNDER_FRQ_THR for a time period longer than
UNDER_FRQ_DELAY. The alarm is cleared when the frequency rises above the nominal
frequency minus UNDER_FRQ_THR for a time period longer than UNDER_FRQ_DELAY.
UNDER_FREQ_THR is an absolute frequency, in Hz, that is subtracted from the nominal
frequency to determine the lowest acceptable frequency for the grid.
Detection of abnormally high frequency compared to the nominal frequency, to monitor
power supply quality. The alarm will be triggered if a circuit's frequency is above the
nominal frequency plus OVER_FRQ_THR for a time period longer than
OVER_FRQ_DELAY. The alarm will be cleared when a circuit's frequency falls below the
nominal frequency plus OVER_FRQ_THR for a time period longer than
OVER_FRQ_DELAY. OVER_FREQ_THR is an absolute frequency, in Hz, that is added
to the nominal frequency to determine the highest acceptable frequency for the grid.
PACSystems* RX3i Power Sync and Measurement System – February 2013
GFK-2749