Siemens 6MD85, Manual

Page: 827 / 1256

When determining the setting value, please keep in mind the measurement method and the measuring
connection that you have selected. If you work with the positive-sequence voltage, remember that the
maximum voltage is equal to the phase-to-ground voltage. The default setting is referred to this value.
Parameter: Dropout differential
•
Recommended setting value
(_:2311:109) Dropout differential
=
20 mHz
Due to the high-precision frequency measurement, the recommended setting value for the
Dropout
differential
can remain at 20 mHz. For a later dropout of the stage, increase the setting value of the
dropout differential. For example, if the pickup value (parameter
Threshold
) of the stage is set to 51.5 Hz
and the
Dropout differential
to 100 mHz, the stage will drop out at 51.4 Hz.
Setting example of the overfrequency protection for generators
If the overspeed limiter does not function properly, the overfrequency protection issues an additional alarm
indication. Overspeeding can be caused by load shedding or by a disturbance of the speed limiter (for
example, in an island network).
One possible frequency limit could be 1.03 f
rated
. If the machine does not recover, it can be shut down with a
2nd stage of, for example, 1.08 f
rated
. To avoid overfunctions, you can set a sufficient time delay for the
warning indication or tripping.
For this application, 2 stages of the overfrequency protection are used. 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 or disconnection 51.50 Hz 61.80 Hz 20.00
f2> Shutdown 54.00 Hz 64.80 Hz 5.00
i
i
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 differen-
tial 20 mHz to 2000 mHz 20 mHz
Stage 1
_:31:1 Stage 1:Mode
•
off
•
on
•
test
off
_:31:2 Stage 1:Operate & flt.rec.
blocked
•
no
•
yes
no
_:31:3 Stage 1:Threshold 40.00 Hz to 70.00 Hz 1.00 Hz
_:31:6 Stage 1:Operate delay 0.00 s to 600.00 s 10.00 s
Stage 2
_:32:1 Stage 2:Mode
•
off
•
on
•
test
off
_:32:2 Stage 2:Operate & flt.rec.
blocked
•
no
•
yes
no
7.18.5
Protection and Automation Functions
7.18 Overfrequency Protection
SIPROTEC 5, High-Voltage Bay Controller, Manual 827
C53000-G5040-C015-9, Edition 11.2017