Functions
2.18 Reverse-Power Protection Application with Flexible Protection Function
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
301
Pickup Value, Dropout Ratio
The pickup value of the reverse power protection is set to 10% of the nominal generator output. In this example,
the setting value is configured as secondary power in watts. The following relationship exists between the
primary and the secondary power:
On the basis of the indicated data, the pickup values are calculated considering P
prim
= 3.81 MW (10% of 38.1
MW) on the primary level to
on the secondary level. The dropout ratio is set to 0.9. This yields a secondary dropout threshold of P
sec, dropout
= 15.6 W. If the pickup threshold is reduced to a value near the lower setting limit of 0.5 W, the dropout ratio
should equally be reduced to approximately 0.7.
Delay for Pickup, Dropout and Trip
The reverse power protection does not require short tripping times as protection from undesired power feed-
back. In the present example, it is useful to delay pickup and dropout by about 0.5 s and the trip by approx. 1
s. Delaying the pickup will minimize the number of fault logs which are opened when the reverse power oscil-
lates around the threshold.
When using the reverse power protection to disconnect the substation quickly from the power supply compa-
ny's system if faults occur, it is useful to select a larger pickup value (e.g. 50% of nominal power) and shorter
time delays.
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