ABB RET670 Product Manual page 17

ABB
Transformer protection RET670 ANSI
Pre-configured
Product version: 1.2
generating plant, generator governor problems can
also cause over frequency.
SAPTOF (81) is used mainly for generation shedding
and remedial action schemes. It is also used as a
frequency stage initiating load restoring.
SAPTOF (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
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. 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.
7. 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 pickups. 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 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.
8. 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.
1MRK 504 118-BUS A
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