Date Code 20010625
Trip and Target Logic
5-1
SEL-311L Instruction Manual
SECTION 5: TRIP AND TARGET LOGIC
I
NTRODUCTION
The SEL-311L Relay trip logic combines trip decisions from several sources into a single Relay
Word bit, useful for controlling trip contacts. The relay also contains line current differential
high-speed tripping logic, which bypasses the normal trip logic and directly controls trip
contacts. This high-speed trip logic results in 87L trip times up to 3/4 cycle faster than available
using SEL
OGIC
®
control equations.
L
INE
C
URRENT
D
IFFERENTIAL
T
RIPS
High-Speed 87L Tripping
For the fastest 87L protection, set EHST equal to the desired number of trip contacts. No trip
logic settings are required for line current differential protection when setting EHST
r
1. Relay
Word bit TRIP87 asserts when line current differential algorithms detect an internal fault, or
when a valid direct transfer trip is received on the 87L communications channel. As shown in
Figure 5.2, when setting ESHT
r
1, Relay Word bit TRIP87 directly controls one or more high-
speed outputs OUT201–OUT206. For example, when EHST = 2, TRIP87 directly controls high-
speed outputs OUT201 and OUT202. These high-speed outputs close in less than 10 µs, are trip
rated, and interrupt dc trip current, so tripping auxiliary relays are often not required. Use this
method to achieve the trip times shown in Figure 3.6 and Figure 3.7.
When high-speed tripping is enabled, Relay Word bit TRIP87 is also routed to the backup
protection tripping logic in Figure 5.4. This triggers event reports and the target logic when a
high-speed 87L trip occurs.
87L Tripping Via SEL
OGIC
To qualify 87L protection using a SEL
OGIC
control equation, make setting EHST = N. This
disables direct control of high-speed outputs OUT201–OUT206. Place Relay Word bit TRIP87
directly in SEL
OGIC
control equation TR, supervised by the appropriate relay elements and
conditions. Place Relay Word bit TRIP in the SEL
OGIC
control equation for high-speed outputs
OUT201–OUT206, and/or in the SEL
OGIC
control equations for conventional outputs OUT101–
OUT107. Add 3/4 cycle to the trip times shown in Figure 3.6 and Figure 3.7 when using 87L
protection qualified by SEL
OGIC
control equations. See
Settings Example: 230 kV
Transmission Line With Tapped Load
in
Section 9: Setting the Relay
for a more detailed
example of qualified 87L tripping. See
Backup Protection Trips
later in this section for more
information about Relay Word bit TRIP.
87L High-Speed Direct Transfer Tripping
Set EHSDTT = Y to enable direct transfer tripping via the 87L communications channel for two-
or three-terminal 87L protection. When setting EHSDTT = Y, the relay asserts Relay Word bit
TRIP87 less than 1/2 cycle (plus channel delays) after 87L elements in the relays attached to
either Channel X or Channel Y detect an internal fault. Direct transfer tripping is automatically
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