Siemens 7SJ85 - Page 375

Parameter: Threshold
•
Default setting (_:3) Threshold = 1.350 A
The setting is mainly determined by the maximum operating current.
Pickup by overload must be excluded since the protection may trip if a short operate delay time is set. Set the
Threshold parameter for generators to a value between 20 % and 30 %, for transformers and motors
approx. 40 % above the expected peak load.
Parameter: Operate delay
•
Default setting (_:6) Operate delay = 3.00 s
The parameter Operate delay must be coordinated with the time grading of the network protection to
guarantee the selectivity. Practical time delays are between 1 s to 2 s.
Parameter: Blk. by meas.-volt. failure
•
Default setting (_:10) Blk. by meas.-volt. failure = yes
With the parameter Blk. by meas.-volt. failure, you can activate (yes) or deactivate (no) the
blocking by the Measuring voltage failure detection function. The recommended setting is the default
setting.
Parameter: State of V-seal-in
•
Default setting (_:101) State of V-seal-in = off
With the parameter State of V-seal-in, the seal-in functionality can be activated (switched on). Siemens
recommends this setting if the excitation transformer is connected to the main lead of the generator.
Parameter: V-seal-in threshold
•
Default setting (_:102) V-seal-in threshold = 46.2 V
The V-seal-in threshold (positive-sequence voltage) is set to a value below the lowest phase-to-phase
voltage admissible during an operation, for example 80 % of the rated voltage of a generator. The positive-
sequence voltage is evaluated. The practicable value for a voltage transformer with a rated secondary voltage
of 100 V is 46.2 V.
The following table shows an example of a specification:
Threshold
1.4 * I
rated, Gen
Operate delay 3.00 s
Undervoltage seal-in 0.8 * V
rated, Gen
Duration of V-seal-in time 4.00 s
Dropout ratio 0.95
Rated current I
rated, Gen
483 A Rated voltage V
rated, Gen
6.3 kV
Rated current I
rated, VT, prim
500 A Rated voltage V
rated, VT, prim
6.3 kV
Rated current I
rated, VT, sec
1 A Rated voltage V
rated, VT, sec
100 V
The following secondary setting values result from this specification:
[fo_OCP_UVSI_threshold, 1, en_US]
[fo_OCP_UVSI_Seal-in, 1, en_US]
Protection and Automation Functions
6.4 Voltage-Dependent Overcurrent Protection, Phases
SIPROTEC 5, Overcurrent Protection, Manual 375
C53000-G5040-C017-8, Edition 07.2017