Manual 37351A
MFR 11 Packages - Protection Relay
© Woodward
Page 39/59
Underfrequency Monitoring
The monitoring of the frequency is carried out on two levels. The frequency measuring is monitored three-phase
if all voltages are greater than 15 % of the rated value (100 V or 400 V). This ensures quick and precise meas-
urement of the frequency. The frequency is still monitored correctly even if voltage is only applied to one phase.
Function
"Frequency not within permissible limits"
The monitored frequency is not within the configured permissible limits for overfrequency. The alarm message
"
Und.freq.1
" or "
Und.freq.2
" will be displayed. This message can be suppressed with the discrete input
"Blocking of protective functions / remote acknowledgement".
Underfrequency-
Monitoring ON
Underfrequency monitoring
ON/OFF
ON
................ Underfrequency monitoring is enabled. The subsequent screens of
this function are indicated.
OFF
.............. Underfrequency monitoring is disabled. The subsequent screens of
this function are not displayed.
Underfrequency 1
f < 00.00Hz
Threshold underfrequency, level 1
40.00 to 80.00 Hz
Underfrequency (level 1) is defined by this parameter. If this limit is reached or
fallen below, the unit outputs the message "
Und.freq.1
". If a relay was assigned
to this function in the relay manager, that relay will be energized.
Underfrequency 1
Delay 00.00s
Pickup delay, level 1
0.02 to 99.98 s
In order to initiate an underfrequency (level 1) alarm, the measured frequency must
fall below and remain below the configured threshold without interruption for at
least the period of time specified in this screen.
Underfrequency 2
f < 00.00Hz
Threshold underfrequency, level 2
40.00 to 80.00 Hz
Underfrequency (level 2) is defined by this parameter. If this limit is reached or
fallen below, the unit outputs the message "
Und.freq.2
". If a relay was assigned
to this function in the relay manager, that relay will be energized.
Underfrequency 2
Delay 00.00s
Pickup delay, level 2
0.02 to 99.98 s
In order to initiate an underfrequency (level 2) alarm, the measured frequency must
fall below and remain below the configured threshold without interruption for at
least the period of time specified in this screen.
Underfrequency
Hysteres. 0.00Hz
Hysteresis for the underfrequency monitoring, levels 1 + 2
0.01 to 9.99 Hz
In order to prevent system fluctuations from continually initiating underfrequency
alarms (both levels), a higher release point is defined here. If the control monitors
the frequency below the permissible limit, the frequency must rise above that
threshold and the frequency level defined here for the fault condition to be recog-
nized as no longer existing.
Example: If a 60 Hz system has an underfrequency limit of 50 Hz and a hysteresis
of 5 Hz, the monitored frequency for an overfrequency alarm must rise above
55 Hz to reset the alarm.
