Siemens 7SC80 Manual page 439

Through the use of filters and repeated measurements, the frequency evaluation of side 2 is free from
harmonic influences and very accurate.
Overfrequency/Underfrequency of Side 2
Frequency protection of side 2 consists of four frequency elements. To make protection flexible for different
power system conditions, these elements can be used alternatively for frequency decrease or increase sepa-
rately, and can be independently set to perform different control functions.
Operating Range
The frequency of side 2 can be determined as long as in a three-phase voltage transformer connection, the
positive-sequence system of the voltages is present and of sufficient magnitude. If the measured voltage
drops below a settable value Vmin S2, the frequency protection of side 2 is blocked because no precise
frequency values can be calculated from the signal.
Time Delays/Logic
Each frequency element has an associated settable time delay. When the time delay elapses, a trip signal is
generated. When a frequency element drops out, the tripping command is immediately terminated, but not
before the minimum command duration has elapsed.
Each of the four frequency elements can be blocked individually via binary inputs.
The following figure shows the logic diagram for the frequency protection function of side 2. In the figure,
Freq. S2 stands for the frequency of side 2.
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
2.30 Additional Applications with 6 Voltage Inputs
Functions
439