Rate-Of-Change Frequency Protection Sapfrc (81) - ABB REL650 Applications Manual

Section 9
Frequency protection
9.3
9.3.1
9.3.2
272
Equipment protection, such as for motors and generators
The setting has to be well above the highest occurring "normal" frequency and well below
the highest acceptable frequency for the equipment.
Power system protection, by generator shedding
The setting must be above the highest occurring "normal" frequency and below the highest
acceptable frequency for power stations, or sensitive loads. The setting level, the number
of levels and the distance between two levels (in time and/or in frequency) depend very
much on the characteristics of the power system under consideration. The size of the
"largest loss of load" compared to "the size of the power system" is a critical parameter.
In large systems, the generator shedding can be set at a fairly low frequency level, and the
time delay is normally not critical. In smaller systems the frequency PICKUP level has to
be set at a higher value, and the time delay must be rather short.

Rate-of-change frequency protection SAPFRC (81)

Identification
Function description
Rate-of-change frequency protection
Application
Rate-of-change frequency protection (SAPFRC, 81), is applicable in all situations, where
reliable detection of change of the fundamental power system voltage frequency is
needed. SAPFRC (81) can be used both for increasing frequency and for decreasing
frequency. SAPFRC (81) provides an output signal, suitable for load shedding or
generator shedding, generator boosting, HVDC-set-point change, gas turbine start up and
so on. Very often SAPFRC (81) is used in combination with a low frequency signal,
especially in smaller power systems, where loss of a fairly large generator will require
quick remedial actions to secure the power system integrity. In such situations load
shedding actions are required at a rather high frequency level, but in combination with a
large negative rate-of-change of frequency the underfrequency protection can be used at
a rather high setting.
IEC 61850 IEC 60617
identification identification
SAPFRC
df/dt > <
SYMBOL-N V1 EN
1MRK 506 334-UUS A
ANSI/IEEE C37.2
device number
81
Application manual