5.11
Date Code 20060320 Instruction Manual SEL-311C Relay
Trip and Target Logic
Communications-Assisted Trip Logic-General Overview
In most cases, these tripping schemes require Zone/Level 3 elements set
direction reverse (setting DIR3 = R); see Figure 5.4. Note that Zone 1 and
Zone 2 are fixed in the forward direction.
See Directional Control Settings on page 4.21 for more information on Zone/
Level direction settings DIR3 and DIR4.
POTT, PUTT, DCUB, and DCB communications-assisted tripping schemes
are explained in subsections that follow.
Use M
IRRORED BITS communications to implement any of these tripping
schemes efficiently and economically. M
IRRORED BITS technology is
generally used with either POTT or DCUB tripping schemes. If the
communications channel is reliable and noise-free, e.g., dedicated fiber optic,
then POTT gives unsurpassed security and very good dependability. If the
communications channel is less than perfect, but communications channel
failures are not likely to be coincident with external faults, then DCUB gives a
very good combination of security and dependability.
Trip Setting TRCOMM
The POTT, PUTT, DCUB, and DCB tripping schemes use SELOGIC control
equation trip setting TRCOMM for those tripping elements that are supervised
by the communications-assisted trip logic (see top half of Figure 5.1). Setting
TRCOMM is typically set with Zone 2 overreaching distance elements (fixed
direction forward):
M2P Zone 2 phase distance instantaneous element
Z2G Zone 2 ground distance instantaneous element
The exception is a DCB scheme, where Zone 2 overreaching distance
elements (set direction forward) with a short delay are used instead. The short
delays provide necessary carrier coordination delays (waiting for the block
trip signal). See Figure 5.14. These elements are entered in trip setting
TRCOMM.
Trip Settings
TRSOTF and TR
In a communications-assisted trip scheme, the SELOGIC control equation trip
settings TRSOTF and TR can also be used, in addition to setting TRCOMM.
Setting TRSOTF can be set as described in Switch-Onto-Fault Trip Logic on
page 5.7.
Setting TR is typically set with unsupervised Level 1 underreaching elements
(fixed direction forward):
M1P Zone 1 phase distance instantaneous element
Z1G Zone 1 ground distance instantaneous element
67G1 Level 1 directional residual ground instantaneous overcurrent
element
67Q1 Level 1 directional negative-sequence instantaneous overcurrent
element
and other time-delayed elements (e.g., Level 2 definite-time overcurrent
elements).
Trip Setting DTT
The DTT and DUTT tripping schemes are realized with SELOGIC control
equation trip setting DTT, discussed at the beginning of this section.
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