Due to the high-precision frequency measurement, the recommended setting value for the Dropout
differential can remain at 20 mHz. If in your application you wish a subsequent dropout of the tripping
stage, then increase the setting value of the dropout differential. For instance, if the pickup value (parameter
Threshold ) of the tripping stage is set to 49.8 Hz and the Dropout differential to 100 mHz, the
stage will drop out at 49.9 Hz.
Application example of the underfrequency protection
Frequency protection can be used for load shedding. The UCTE has defined a 5-stage plan for the Western
European power grid. The setting values of the stages are based on that plan (see table below).
Table 6-16 Stage Plan
Frequency Activity
49.80 Hz Alarm and activation of reserves following an established plan
49.00 Hz Undelayed disconnection of 10 % to 15 % of the power system load
48.70 Hz Undelayed disconnection of another 10 % to 15 % of the power system load
48.40 Hz 3rd load shedding stage. Another 15 % to 20 % of the power system load is
disconnected.
47.50 Hz Power plants are decoupled from the electrical power system
For this application, 3 stages of the underfrequency protection are used. 2 of these stages are used for load
shedding. The following table shows a setting suggestion.
Stage Caused by Setting Values
At f
rated
= 50 Hz At f
rated
= 60 Hz Delay
f1< Warning 49.80 Hz 59.80 Hz 10.00
f2< 1st load shedding 49.00 Hz 59.00 Hz 0.00
f3< 2nd load shedding 48.70 Hz 58.70 Hz 0.00
NOTE
This table shows one example of a possible frequency protection setting. The setting values can differ
depending on the application.
Settings
Addr.
Parameter C Setting Options Default Setting
General
_:2311:101 General:Minimum voltage 3.000 V to 175.000 V 37.500 V
_:2311:109 General:Dropout differential 20 mHz to 2000 mHz 20 mHz
Stage 1
_:61:1 Stage 1:Mode
•
off
•
on
•
test
off
_:61:2 Stage 1:Operate & flt.rec.
blocked
•
no
•
yes
no
_:61:3 Stage 1:Threshold 40.00 Hz to 70.00 Hz 49.80 Hz
_:61:6 Stage 1:Operate delay 0.00 s to 600.00 s 10.00 s
Stage 2
_:62:1 Stage 2:Mode
•
off
•
on
•
test
off
6.33.5
Protection and Automation Functions
6.33 Underfrequency Protection
SIPROTEC 5, Overcurrent Protection, Manual 771
C53000-G5040-C017-8, Edition 07.2017
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