5-12 Trip and Target Logic Date Code 20020426
SEL-351-5, -6, -7 Instruction Manual
ECOMM = DCUB2 [DCUB scheme for three-terminal line (communications from
two
remote terminals)]
ECOMM = DCB [DCB scheme]
These tripping schemes can all work in two-terminal or three-terminal line applications. The
DCUB scheme requires separate settings choices for these applications (ECOMM = DCUB1 or
DCUB2) because of unique DCUB logic considerations.
In most cases, these tripping schemes require (see Figure 5.4):
Level 1 underreaching overcurrent elements set direction forward (setting DIR1 = F)
Level 2 overreaching overcurrent elements set direction forward (setting DIR2 = F)
Level 3 overcurrent elements set direction reverse (setting DIR3 = R)
See Directional Control Settings, in Section 4: Loss-of-Potential, Load Encroachment, and
Directional Element Logic for more information on level direction settings DIR1 through DIR4.
POTT, PUTT, DCUB, and DCB communications-assisted tripping schemes are explained in
subsections that follow.
Trip Setting TRCOMM
The POTT, PUTT, DCUB, and DCB tripping schemes use SEL
OGIC 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 Level 2 overreaching
overcurrent elements (set direction forward):
67P2 Level 2 directional phase instantaneous overcurrent element
67N2 Level 2 directional neutral ground instantaneous overcurrent element
67G2 Level 2 directional residual ground instantaneous overcurrent element
67Q2 Level 2 directional negative-sequence instantaneous overcurrent element
The exception is a DCB scheme, where Level 2 overreaching overcurrent elements (set direction
forward) with a short delay are used instead:
67P2S Level 2 directional phase instantaneous overcurrent element (with delay 67P2SD)
67N2S Level 2 directional neutral ground instantaneous overcurrent element (with delay
67N2SD)
67G2S Level 2 directional residual ground instantaneous overcurrent element (with delay
67G2SD)
67Q2S Level 2 directional negative-sequence instantaneous overcurrent element (with
delay 67Q2SD)
The short delays provide necessary carrier coordination delays (waiting for the block trip signal).
Trip Settings TRSOTF and TR
In a communications-assisted trip scheme, the SEL
OGIC control equation trip settings TRSOTF
and TR can also be used, in addition to setting TRCOMM.
Setting TRSOTF can be set as described in preceding subsection Switch-Onto-Fault (SOTF)
Trip Logic.
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