Rate-of-change frequency protection
SAPFRC (81)
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.
7. Secondary system
supervision
Current circuit supervision CCSRDIF
(87)
Open or short circuited current transformer
cores can cause unwanted operation of many
protection functions such as differential,
ground-fault current and negative-sequence
current functions.
It must be remembered that a blocking of
protection functions at an occurrence of open
CT circuit will mean that the situation will
remain and extremely high voltages will stress
the secondary circuit.
Current circuit supervision (CCSRDIF, 87)
compares the residual current from a three
phase set of current transformer cores with the
neutral point current on a separate input taken
from another set of cores on the current
transformer.
A detection of a difference indicates a fault in
the circuit and is used as alarm or to block
protection functions expected to give unwanted
tripping.
Fuse failure supervision SDDRFUF
The aim of the fuse failure supervision function
(SDDRFUF) is to block voltage measuring
functions at failures in the secondary circuits
between the voltage transformer and the IED in
order to avoid unwanted operations that
otherwise might occur.
The fuse failure supervision function basically
has three different algorithms, negative
sequence and zero sequence based algorithms
and an additional delta voltage and delta
current algorithm.
The negative sequence detection algorithm is
recommended for IEDs used in isolated or high-
impedance grounded networks. It is based on
the negative-sequence measuring quantities, a
high value of voltage without the presence of
the negative-sequence current 3I
2
.
The zero sequence detection algorithm is
recommended for IEDs used in directly or low
impedance grounded networks. It is based on
the zero sequence measuring quantities, a high
value of voltage 3V
0
without the presence of
the residual current 3I
0
.
A criterion based on delta current and delta
voltage measurements can be added to the fuse
failure supervision function in order to detect a
three phase fuse failure, which in practice is
more associated with voltage transformer
switching during station operations.
For better adaptation to system requirements,
an operation mode setting has been introduced
which makes it possible to select the operating
conditions for negative sequence and zero
sequence based function. The selection of
different operation modes makes it possible to
choose different interaction possibilities
between the negative sequence and zero
sequence based algorithm.
Breaker protection REQ650 ANSI
1MRK 505 269-BUS -
Product version: 1.1
Issued: April 2011
20
ABB
