ABB RET670 Product Manual page 15

ABB
Transformer protection RET670
Pre-configured
Product version: 1.1
The distance protection zones can operate,
independent of each other, in directional
(forward or reverse) or non-directional mode.
This makes them suitable, together with
different communication schemes, for the
protection of power lines and cables in
complex network configurations, such as
parallel lines, multi-terminal lines.
Directional impedance element for Mho
characteristic ZDMRDIR
The phase-to-earth impedance elements can
be optionally supervised by a phase
unselective directional function (phase
unselective, because it is based on
symmetrical components).
Faulty phase identification with load
encroachment FMPSPDIS
The operation of transmission networks
today is in many cases close to the stability
limit. Due to environmental considerations
the rate of expansion and reinforcement of
the power system is reduced, for example
difficulties to get permission to build new
power lines. The ability to accurate and
reliable classifying the different types of fault
so that single phase tripping and
autoreclosing can be used plays an important
roll in this matter.
The phase selection function is design to
accurate select the proper fault loop in the
distance function dependent on the fault type.
The heavy load transfer that is common in
many transmission networks may in some
cases interfere with the distance protection
zone reach and cause unwanted operation.
Therefore the function has a built in
algorithm for load encroachment, which gives
the possibility to enlarge the resistive setting
of the measuring zones without interfering
with the load.
The output signals from the phase selection
function produce important information
about faulty phase(s), which can be used for
fault analysis as well.
1MRK 504 091-BEN B
Power swing detection ZMRPSB
Power swings may occur after disconnection
of heavy loads or trip of big generation plants.
Power swing detection function (ZMRPSB) is
used to detect power swings and initiate
block of selected distance protection zones.
Occurrence of earth-fault currents during a
power swing can block ZMRPSB function to
allow fault clearance.
Power swing logic ZMRPSL
Additional logic is available to secure tripping
for faults during power swings and prevent
tripping at power swings started by a fault in
the network.
Current protection
Instantaneous phase overcurrent
protection PHPIOC
The instantaneous three phase overcurrent
function has a low transient overreach and
short tripping time to allow use as a high set
short-circuit protection function.
Four step phase overcurrent protection
OC4PTOC
The four step phase overcurrent protection
function OC4PTOC has an inverse or definite
time delay independent for each step
separately.
All IEC and ANSI time delayed characteristics
are available together with an optional user
defined time characteristic.
The directional function is voltage polarized
with memory. The function can be set to be
directional or non-directional independently
for each of the steps.
A 2nd harmonic blocking can be set
individually for each step.
Instantaneous residual overcurrent
protection EFPIOC
The Instantaneous residual overcurrent
protection EFPIOC has a low transient
overreach and short tripping times to allow
use for instantaneous earth-fault protection,
Issued: June 2010
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