ABB RER620, Technical Manual

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Section 4
Protection functions
RER620 223
Technical Manual
4.4.1.9 Technical data
Table 241: 81 Technical data
4.4.2 Load shedding and restoration 81S
4.4.2.1 Identification
4.4.2.2 Function block
Figure 101: Function block
4.4.2.3 Functionality
The load shedding and restoration function 81S is capable of performing load shedding
based on underfrequency and the rate of change of the frequency. The load that is shed
during the frequency disturbance can be restored once the frequency has stabilized to the
normal level.
The measured system frequency is compared to the set value to detect the underfrequency
condition. The measured rate of change of frequency (df/dt) is compared to the set value
to detect a high frequency reduction rate. The combination of the detected underfrequency
and the high df/dt is used for the activation of the load shedding. There is a definite time
delay between the detection of the underfrequency and high df/dt and the activation of 81S.
Characteristic Value
Operation accuracy f>/f< ±10 mHz
df/dt ±100 mHz/s (in range |df/dt| < 5
Hz/s)
± 2.0% of the set value (in range
5 Hz/s < |df/dt| < 15 Hz/s)
Start time f>/f< < 80 ms
df/dt < 120 ms
Reset time < 150 ms
Operate time accuracy ±1.0% of the set value or ±30 ms
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Load shedding and restoration LSHDPFRQ UFLS/R 81S