P.3.3
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
87L Theory of Operation
NOTE: Network Ports A and B
connect the relay to the Process Bus,
and only 87L and future Sampled
Value (SV) network traffic are
transmitted and received on these
ports. Network Ports C and D connect
the relay to the Station Bus. IP-based
network traffic and GOOSE network
traffic are transmitted and received on
these ports. Take care not to use the
same VLAN tags for outgoing 87L and
outgoing GOOSE data to avoid mixing
Process bus traffic with Station bus
traffic. However, the VLAN IDs of
incoming GOOSE data can be the
same as outgoing 87L VLAN IDs.
You can use the relay to perform 87L applications either over serial or
Ethernet communications media. Order with your relay as many as two serial
ports dedicated to the 87L function. These ports support copper and fiber
communications media including direct fiber, multiplexed fiber (C37.94),
EIA-422, and G.703 interfaces. The relay provides applications for two- and
three-terminal lines through two serial ports intended for point-to-point
communications. Two-terminal lines offer an option for using two channels in
a standby channel switchover scheme, providing built-in 87L scheme channel
redundancy. In three-terminal applications, you can use the 87L scheme in the
master mode (all relays configured to receive both remote sets of data, and
tripping directly) or in the master-outstation mode (two relays with no access
to all remote data, and tripping via direct transfer trip bit sent from the master
over the 87L channel). When in the master mode, the scheme switches
automatically to the master-outstation mode upon loss of an 87L channel.
NOTE: The 87L packet is 802.1Q
compliant, so you can establish VLANs
just for 87L traffic. However, if the 87L
VLAN-tagged traffic passes through
VLAN-unaware parts of the network,
VLAN-unaware equipment may not
process the VLAN tags and will treat
the 87L traffic as normal multicast
traffic.
You can apply the 87L function, when it is configured to work over Ethernet
to two-, three-, or four-terminal lines. Two Ethernet ports are dedicated to the
87L data exchange over Ethernet. The relay uses these ports for no other
communications functions. One of the ports is configured as primary, while
the other works in a media failover scheme to provide a redundant Ethernet
connection between the relay and associated Ethernet equipment. All relays
using Ethernet for their 87L function require a properly engineered Ethernet
network with a dedicated virtual local area network (VLAN).
The relay offers two modes of current data synchronization: channel-based
and external-time-based. The channel-based mode works without any external
time sources but requires the 87L communications channel to be symmetrical
(the channel delays in the transmit and receive directions must be identical or
nearly identical). If you cannot guarantee channel symmetry, you can use
external high-precision time sources connected via standard IRIG-B inputs to
apply the relay in the external-time-based synchronization mode. There are a
number of fallback modes for situations in which one or more time sources are
unavailable or report degraded time accuracy via the time-quality bits in the
IRIG-B signal. When you apply the 87L function over Ethernet, the function
uses only the external-time-based synchronization mode; you cannot use
Ethernet applications in the channel-based mode.
The 87L function of the relay uses phase (87LP), negative-sequence (87LQ),
and zero-sequence (87LG) currents for excellent security, sensitivity, and
speed. The function works on current samples to provide fast and sensitive
external fault detection that guards against current transformer (CT)
saturation, harmonic measurement for in-line transformers, high-speed
operation, and other advantages.
The 87L function of the relay allows in-line transformer applications that
compensate for vector group, ratio, and zero-sequence of the in-zone
transformer. You can also use harmonic blocking, restraint, or both, for
stabilization under magnetizing inrush conditions. You can protect multi-
winding transformers through the use of multiple current inputs available on
locally and remotely installed relays.
Use the 87L function to provide line charging current compensation for
enhanced sensitivity and security in long extra high voltage line or cable
applications. The compensation is based on voltage signals with a built-in
fallback response if some of the voltage sources suffer loss of potential
conditions or become otherwise unavailable. In this way, the 87L function
retains a current-only scheme benefit. The function performs compensation on
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