ABB RED615 Product Manual - page 12
3. Protection functions
The relay offers two-stage phase-segregated line differential
protection, phase overcurrent protection, negative-sequence
overcurrent protection and circuit breaker failure protection.
Depending on the chosen standard configuration, the basic
functionality can be extended by thermal overload protection,
non-directional or directional overcurrent protection, directional
or non-directional earth-fault protection, sensitive earth-fault
protection, phase discontinuity protection, transient/
intermittent earth-fault protection, residual overvoltage
protection, phase-voltage and frequency based protection and
three-pole multishot autoreclosing functions for overhead line
feeders. For standard configurations B, D and E, admittance-
based, wattmetric-based or harmonics-based earth-fault
protection is offered as an option in addition to the directional
earth-fault protection.
The line differential protection function includes a stabilized low
stage and an instantaneous high stage. The stabilized low
stage provides sensitive differential protection and remains
stable during, for example, current transformer saturation
conditions. The low-stage operation can be restrained using
second harmonic detection if an out-of-zone power transformer
is to be energized. The instantaneous high stage offers less
sensitive differential protection but enables fast operation
during high fault currents. If there is an in-zone transformer in
the protection zone, the vector group is automatically
compensated based on the winding types and clock number
setting values.
The operating time characteristic for the low stage can be set to
definite time or inverse definite time mode. The direct intertrip
function ensures that both ends are always simultaneously
tripped, independent of the fault current contribution.
4. Application
RED615 can be used in a variety of applications requiring an
absolutely selective unit type protection system. The zone-of-
protection of a line differential protection system is the feeder
section defined by the location of the current transformers in
the local and the remote substation. RED615 can also be used
for line differential protection if there is an in-zone transformer in
the protected feeder section.
Combining horizontal GOOSE communication over a station
bus and binary signal transfer over the protection
communication link offers new application possibilities beyond
traditional line differential protection. One interesting
application based on inter-substation signal transfer is loss-of-
mains (LOM) protection in networks with distributed generation.
The performance of the combination of binary signal transfer
and horizontal GOOSE communication performance as to
speed, selectivity and reliability are hard to match with
conventional loss-of-mains protection.
RED615 is the ideal relay for the protection of feeders in
network configurations containing closed loops. Under normal
operating conditions the feeder loop is closed. The aim of the
closed loop is to secure the availability of power for the end
users. As a result of the closed loop configuration, any fault
spot in the system will be fed with fault current from two
directions. Using plain overcurrent protection, either directional
or non-directional, it is difficult to obtain fast and selective short
circuit protection. With RED615 line differential protection
relays the faulty part of the network can be selectively isolated,
thus securing power distribution to the healthy part of the
network.
The standard configuration E includes one conventional
residual current (Io) input and three combi-sensor inputs for
phase currents and phase voltages. The connection of the three
combi-sensors is made with RJ-45 type of connectors.
Sensors offer certain benefits compared to conventional
current and voltage instrument transformers. For example,
current sensors do not saturate at high currents, they consume
less energy and they weigh less. In voltage sensors the risk of
ferro-resonance is eliminated. The sensor inputs also enable
the use of the relay in compact medium voltage switchgears,
such as ABB’s UniGear Digital, SafeRing and SafePlus, with
limited space for conventional measuring transformers, thus
requiring the use of sensor technology. Further, the adapters
also enable the use of sensors with Twin-BNC connectors.
Under certain operational circumstances, such as maintenance
of primary equipment or substation extension projects there will
be a need to interconnect network parts, which normally are
separated. To avoid major re-parameterization of the protection
devices of the network when the network topology is changed,
line differential protection relays can be used to obtain
absolutely selective feeder protection in looped networks.
Line Differential Protection and Control
1MRS756500 K
RED615
Product version: 5.0 FP1
12
ABB