Underfrequency Protection Functions (Under Frequency 1 & 2) Ansi# 81U (<F, <<F) - Iskra SR100 User Manual

SETTINGS
Underfrequency protection functions (Under Frequency 1 & 2) ANSI#
81U (<f, <<f)
ANSI #81U – Underfrequency is detection of abnormally low frequency compared to the rated frequency, to
monitor power supply quality. The protection may be used for overall tripping or load shedding. Protection
stability is ensured in the event of the loss of the main source and presence of remnant voltage by a restraint in
the event of a continuous decrease of the frequency, which is activated by parameter setting. Monitoring of the
frequency is performed in two steps. It is possible to define up to two underfrequency relay output limits with
down to 50% of nominal frequency.
The parameters represented in the following table can be defined in the Setting and acquisition Software MiQen
(see MiQen: SR100 > Protection > Frequency > Under Frequency 1/2 protection
for all limits; the limits may only differ in their setting ranges):
Limit Text
Under Frequency 1 Monitoring
Parameter limit (%)
Compare time delay (s) 0.00 – 60.00
Hysteresis (%)
Assigned Group
Under frequency 2 Monitoring
Parameter limit (%)
Compare time delay (s) 0.00 – 60.00
Hysteresis (%)
Assigned Group
Monitoring – Under Frequency
The figure below graphically represents the behavior of this particular protection function:
Monitoring – Under Frequency
Supervision Relay – SR100 - User's Manual
Setting range
Yes/No
50.00 – 100.00
0.00 – 10.00
Protection output 1, Protection output 2,
Protection output 3, Protection output 4
Yes/No
50.00 – 100.00
0.00 – 10.00
Protection output 1, Protection output 2,
Protection output 3, Protection output 4
functions; description is identical
Standard value
Yes
90
5
0
Protection output 1
Yes
84
0.3
0
Protection output 2
43