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Protection and Automation Functions
6.28 Overvoltage Protection with Negative-Sequence Voltage/Positive-Sequence Voltage
immediately when the Negative-sequence voltage stage has picked up. The time delay is thus not relevant
and can be left at the default setting.
You implement the release of the Overcurrent-protection stage using a logic block chart. An inverter links
the pickup of the Negative-sequence voltage stage with the Overcurrent-protection stage blocking.
[lo_Pickup of V2_20150507, 1, en_US]
Figure 6-198
Stage
1
The second stage is not needed. It is deleted or remains off.
Example 2:
A negative-sequence voltage in the auxiliary system of the power plant causes negative-sequence currents on
motors. This leads to a thermal overload of the rotors. The following estimation can be used as a basis: 1 %
negative-sequence voltage can lead to approximately 5 % or 6 % negative-sequence current.
A negative-sequence voltage can be caused by a broken conductor on the high-voltage side. If a negative-
sequence voltage occurs, this can, for example, initiate a switching of the infeed in order to prevent a protec-
tion trip of an unbalanced-load protection of the motors.
Siemens recommends using multiple stages for a better grading, whereby a sensitive setting of the threshold
permits an increased tripping delay.
For a reference, only 2 stages are discussed.
The first stage has a pickup threshold of 10 % with a time delay of 1.5 s. The second stage has a pickup
threshold of 3 % with a time delay of 8 s,
Table 6-15
Stage
Stage 1
Stage 2
6.28.4.3
Settings
Addr.
Stage 1
_:17071:1
_:17071:2
_:17071:3
_:17071:4
_:17071:6
Stage 2
_:17072:1
732
Linking the Pickup of the Negative-Sequence Voltage Stage
Setting Values
Percentage of the Negative-
Sequence Voltage to Positive-
Sequence Voltage
10.00 %
seeTable
Recommended Settings
Threshold
10.00 %
3.00 %
Parameter
Stage 1:Mode
Stage 1:Operate &
flt.rec. blocked
Stage 1:Threshold
Stage 1:Dropout ratio
Stage 1:Operate delay
Stage 2:Mode
Time Delay
3.00 s
6-15.
Operate Delay
1.50 s
8.00 s
C
Setting Options
•
off
•
on
•
test
•
no
•
yes
0.50 % to 100.00 %
0.90 to 0.99
0.00 s to 60.00 s
•
off
•
on
•
test
Dropout Ratio
0.95
Default Setting
off
no
10.00 %
0.95
3.00 s
off
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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