Underfrequency Protection Saptuf - ABB REC670 Applications Manual

1MRK 511 401-UEN A
Section 10
10.1
10.1.1
10.1.2
10.1.3
Bay control REC670 2.2 IEC
Application manual
Frequency protection

Underfrequency protection SAPTUF

Identification
Function description
Underfrequency protection
Application
Underfrequency protection SAPTUF is applicable in all situations, where reliable
detection of low fundamental power system frequency is needed. The power
system frequency, and the rate of change of frequency, is a measure of the
unbalance between the actual generation and the load demand. Low fundamental
frequency in a power system indicates that the available generation is too low to
fully supply the power demanded by the load connected to the power grid.
SAPTUF detects such situations and provides an output signal, suitable for load
shedding, generator boosting, HVDC-set-point change, gas turbine start up and so
on. Sometimes shunt reactors are automatically switched in due to low frequency,
in order to reduce the power system voltage and hence also reduce the voltage
dependent part of the load.
SAPTUF is very sensitive and accurate and is used to alert operators that frequency
has slightly deviated from the set-point, and that manual actions might be enough.
The underfrequency signal is also used for overexcitation detection. This is
especially important for generator step-up transformers, which might be connected
to the generator but disconnected from the grid, during a roll-out sequence. If the
generator is still energized, the system will experience overexcitation, due to the
low frequency.
Setting guidelines
All the frequency and voltage magnitude conditions in the system where SAPTUF
performs its functions should be considered. The same also applies to the
associated equipment, its frequency and time characteristic.
Frequency protection
IEC 61850 IEC 60617
identification identification
SAPTUF
f <
SYMBOL-P V1 EN-US
Section 10
IP15746-1 v3
M14865-1 v5
ANSI/IEEE C37.2
device number
81
M13350-3 v4
M13355-3 v8
245