Underfrequency Protection Saptuf - ABB REG670 Applications Manual

1MRK 502 071-UEN -
Section 11
11.1
11.1.1
11.1.2
11.1.3
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
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.
There are two specific application areas for SAPTUF:
Frequency protection
IEC 61850 IEC 60617
identification identification
SAPTUF
f <
SYMBOL-P V1 EN
Section 11
ANSI/IEEE C37.2
device number
81
437