ABB RET670 Product Manual page 18

Transformer protection RET670
Customized
Product version: 1.2
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.
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
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. 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.
8. Multipurpose protection
General current and voltage protection CVGAPC
The protection module is recommended as a
general backup protection with many possible
application areas due to its flexible measuring and
setting facilities.
The built-in overcurrent protection feature has two
settable current levels. Both of them can be used
either with definite time or inverse time
characteristic. The overcurrent protection steps
can be made directional with selectable voltage
polarizing quantity. Additionally they can be
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1MRK 504 117-BEN D
voltage and/or current controlled/restrained. 2nd
harmonic restraining facility is available as well. At
too low polarizing voltage the overcurrent feature
can be either blocked, made non directional or
ordered to use voltage memory in accordance
with a parameter setting.
Additionally two overvoltage and two
undervoltage steps, either with definite time or
inverse time characteristic, are available within
each function.
The general function suits applications with
underimpedance and voltage controlled
overcurrent solutions. The general function can
also be utilized for generator transformer
protection applications where positive, negative
or zero sequence components of current and
voltage quantities are typically required.
9. 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.
ABB