ABB Relion REC670, Applications Manual

Page: 268 / 658

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.
10.3 Rate-of-change of frequency protection SAPFRC (81)
IP15748-1 v4
10.3.1 Identification
M14868-1 v4
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Rate-of-change of frequency protection SAPFRC
df/dt
><
SYMBOL-N V1 EN-US
81
10.3.2 Application
M14966-3 v5
Rate-of-change of 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.
Section 10
1MRK 511 401-UUS A
Frequency protection
262 Bay control REC670 2.2 ANSI
Application manual