ABB Relion 670 Series Technical Reference Manual page 568

Section 9
Frequency protection
9.3.1
9.3.2
9.3.2.1
562
Function description
Rate-of-change frequency protection
Introduction
Rate-of-change frequency protection function (SAPFRC,81) gives an early indication
of a main disturbance in the system. SAPFRC (81) can be used for generation
shedding, load shedding and remedial action schemes. SAPFRC (81) can discriminate
between positive or negative change of frequency.
SAPFRC (81) is provided with an 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
Rate-of-change frequency protection SAPFRC (81) is used to detect fast power system
frequency changes, increase as well as, decrease at an early stage. SAPFRC (81) has a
settable definite time delay. If the rate-of-change of frequency remains below the set
value, for negative rate-of-change, for a time period equal to the chosen time delay, the
TRIP signal is issued. If the rate-of-change of frequency remains above the set value,
for positive rate-of-change, for a time period equal to the chosen time delay, the TRIP
signal is issued. To avoid an unwanted TRIP due to uncertain frequency measurement
at low voltage magnitude, a voltage controlled blocking of the function is available,
that is if the voltage is lower than the set blocking voltage IntBlockLevel, the function
is blocked and no PICKUP or TRIP signal is issued. If the frequency recovers, after a
frequency decrease, a restore signal is issued.
Measurement principle
The rate-of-change of the fundamental frequency of the selected voltage is measured
continuously, and compared with the set value, PUFreqGrad. Rate-of-change
frequency protection SAPFRC (81) is also dependent on the voltage magnitude. If the
voltage magnitude decreases below the setting IntBlockLevel, SAPFRC (81) is
blocked, and the output BLKDMAGN is issued. The sign of the setting PUFreqGrad,
controls if SAPFRC (81) reacts on a positive or on a negative change in frequency. If
SAPFRC (81) is used for decreasing frequency that is, the setting PUFreqGrad has
been given a negative value, and a trip signal has been issued, then a 100 ms pulse is
IEC 61850 IEC 60617
identification identification
SAPFRC
df/dt > <
SYMBOL-N V1 EN
1MRK505222-UUS C
ANSI/IEEE C37.2
device number
81
Technical reference manual