User Manual Chapter 1
GFK-2749A Jan 2020
PSM Module Description and Specifications 10
to lead the signal on the VC terminal by 120 degrees. Unused “reconstructed” signal inputs
are ignored for Phase Sequence detection. The current signals are not monitored for Phase
Sequence.
ANSI 50 – Instantaneous Over-current Protection
This function provides three-phase protection against overloads and phase-to-phase short-
circuits. An alarm will be triggered if any phase current exceeds the specified OVER_CURR_
THR value for a time period longer than OVER_CURR_DELAY. This alarm is cleared when the
current value stays below the OVER_CURR_THR value for a time period longer than
OVER_CURR_DELAY. The OVER_CURR_THR is a percentage of the nominal current.
ANSI 59 – Over-voltage Protection
This function provides detection of abnormally high phase voltage. It works with phase-to-
phase voltage in delta power systems, or phase-to-neutral voltage in wye power systems.
Each voltage is monitored separately. An alarm will be triggered if any voltage exceeds the
specified OVER_VOLT_THR value, as a percentage of the Nominal Voltage parameter, for a
time period longer than OVER_VOLT_DELAY. This alarm is cleared when the voltage drops
below the OVER_VOLT_THR value for a time period longer than the OVER_VOLT_DELAY.
The OVER_VOLT_THR is a percentage of the nominal voltage.
ANSI 60 – Voltage (Current) Imbalance Protection
An alarm will be triggered if any phase voltage or current reading varies from the average of
all three phases by more than VI_IMBALANCE_THR for a time period longer than
VI_IMBALANCE_DELAY. The alarm is cleared when the imbalance condition is corrected for
a time period longer than VI_IMBALANCE_DELAY. IV_IMBALANCE_THR is a percentage of
the average of the three phase voltages (for voltage imbalance) or the three phase currents
(for current imbalance) on a given grid. It works with phase-to-phase voltage in Delta power
systems, or phase-to-neutral voltage in WYE Power systems. No comparison is performed
between the two grids. Neutral current is not monitored for imbalance.
ANSI 81U – Under-frequency Protection
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.
ANSI 81O – Over-frequency Protection
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.
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