Siemens 7SJ85 - Settings

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 Linking the Pickup of the Negative-Sequence Voltage Stage
Stage Setting Values
Percentage of the Negative-
Sequence Voltage to Positive-
Sequence Voltage
Time Delay Dropout Ratio
1 10.00 % 3.00 s 0.95
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, seeTable 6-15.
Table 6-15 Recommended Settings
Stage Threshold Operate Delay
Stage 1 10.00 % 1.50 s
Stage 2 3.00 % 8.00 s
Settings
Addr.
Parameter C Setting Options Default Setting
Stage 1
_:17071:1 Stage 1:Mode
•
off
•
on
•
test
off
_:17071:2 Stage 1:Operate &
flt.rec. blocked
•
no
•
yes
no
_:17071:3 Stage 1:Threshold 0.50 % to 100.00 % 10.00 %
_:17071:4 Stage 1:Dropout ratio 0.90 to 0.99 0.95
_:17071:6 Stage 1:Operate delay 0.00 s to 60.00 s 3.00 s
Stage 2
_:17072:1 Stage 2:Mode
•
off
•
on
•
test
off
6.28.4.3
Protection and Automation Functions
6.28 Overvoltage Protection with Negative-Sequence Voltage/Positive-Sequence Voltage
732 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017