4.6.1.10
Technical revision history
Table 671: FRPFRQ Technical revision history
Technical revision
Change
B
Step value changed from 0.001 to 0.0001 for
the
Start value Freq>
and
Start value Freq<
settings.
C
df/dt setting step changed from 0.005
×Fn /s to 0.0025 ×Fn /s.
D
Internal improvement.
4.6.2
Load-shedding and restoration LSHDPFRQ
4.6.2.1
Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Load-shedding and restoration
LSHDPFRQ
UFLS/R
81LSH
4.6.2.2
Function block
Figure 368: Function block
4.6.2.3
Functionality
The load-shedding and restoration function LSHDPFRQ 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 LSHDPFRQ.
This time delay can be set and it is used to prevent unwanted load-shedding actions
when the system frequency recovers to the normal level.
Throughout this document, “high df/dt” is used to mean “a high rate of
change of the frequency in negative direction.”
1MRS757644 H
Protection functions
620 series
Technical Manual
709
