Two step residual overvoltage protection
ROV2PTOV function calculates the residual
voltage from the three-phase voltage input
transformers or measures it from a single voltage
input transformer fed from an open delta or
neutral point voltage transformer.
ROV2PTOV has two voltage steps, where step 1
can be set as inverse or definite time delayed.
Step 2 is always definite time delayed.
Loss of voltage check LOVPTUV
Loss of voltage check (LOVPTUV) is suitable for
use in networks with an automatic system
restoration function. LOVPTUV issues a three-
pole trip command to the circuit breaker, if all
three phase voltages fall below the set value for a
time longer than the set time and the circuit
breaker remains closed.
6. Frequency protection
Underfrequency protection SAPTUF
Underfrequency occurs as a result of a lack of
sufficient generation in the network.
Underfrequency protection SAPTUF is used for
load shedding systems, remedial action schemes,
gas turbine startup and so on.
SAPTUF is also provided with undervoltage
blocking.
Overfrequency protection SAPTOF
Overfrequency protection function SAPTOF is
applicable in all situations, where reliable
detection of high fundamental power system
frequency is needed.
Overfrequency occurs because of sudden load
drops or shunt faults in the power network. Close
to the generating plant, generator governor
problems can also cause over frequency.
SAPTOF is used mainly for generation shedding
and remedial action schemes. It is also used as a
frequency stage initiating load restoring.
SAPTOF is provided with an undervoltage
blocking.
Rate-of-change frequency protection SAPFRC
Rate-of-change frequency protection function
(SAPFRC) gives an early indication of a main
disturbance in the system. SAPFRC can be used
for generation shedding, load shedding and
remedial action schemes. SAPFRC can
discriminate between positive or negative change
of frequency.
SAPFRC is provided with an undervoltage
blocking.
7. Secondary system supervision
Current circuit supervision CCSRDIF
Open or short circuited current transformer cores
can cause unwanted operation of many
protection functions such as differential, earth-
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) 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 earthed networks. It is based on the
negative-sequence measuring quantities, a high
value of negative sequence voltage 3U
2
without
Breaker protection REQ650
1MRK 505 283-BEN -
Product version: 1.2
20 ABB
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