ABB Relion 670 Series Technical Reference Manual page 557

1MRK505222-UUS C
Section 9
9.1
9.1.1
9.1.2
Technical reference manual
Frequency protection
About this chapter
This chapter describes the frequency protection functions. The way the functions work,
their setting parameters, function blocks, input and output signals and technical data
are included for each function.
Underfrequency protection SAPTUF (81)
Function description
Underfrequency protection
Introduction
Underfrequency occurs as a result of a lack of generation in the network.
Underfrequency protection SAPTUF (81) is used for load shedding systems, remedial
action schemes, gas turbine startup and so on.
SAPTUF (81) is also provided with undervoltage blocking.
The operation is based on positive sequence voltage measurement and requires two phase-
phase or three phase-neutral voltages to be connected. For information about how to
connect analog inputs, refer to Application manual/IED application/Analog inputs/
Setting guidelines
Principle of operation
Underfrequency protection SAPTUF (81) is used to detect low power system
frequency. SAPTUF (81) can either have a definite time delay or a voltage magnitude
dependent time delay. If the voltage magnitude dependent time delay is applied, the
time delay will be longer if the voltage is higher, and the delay will be shorter if the
Frequency protection
IEC 61850 IEC 60617
identification identification
SAPTUF
f <
SYMBOL-P V1 EN
Section 9
ANSI/IEEE C37.2
device number
81
551