Schweitzer Engineering Laboratories SEL-351 - Trip Setting DTT; Use Existing SEL-321 Relay Application Guides for the SEL-351 Relay; Optoisolated Input Settings Differences between the SEL-321 and SEL-351 Relays

Date Code 20001006 Trip and Target Logic 5-13
SEL-351 Instruction Manual
Setting TRSOTF can be set as described in preceding subsection Switch-Onto-Fault (SOTF) Trip
Logic.
Setting TR is typically set with unsupervised Level 1 underreaching overcurrent elements (set
direction forward):
67P1 Level 1 directional phase instantaneous overcurrent element
67N1 Level 1 directional neutral ground instantaneous overcurrent 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.
Use Existing SEL-321 Relay Application Guides for the SEL-351 Relay
The communications-assisted tripping schemes settings in the SEL-351 Relay are very similar to
those in the SEL-321 Relay. Existing SEL-321 Relay application guides can also be used in
setting up these schemes in the SEL-351 Relay. The following application guides are available
from SEL:
AG93-06 Applying the SEL-321 Relay to Directional Comparison Blocking (DCB)
Schemes
AG95-29 Applying the SEL-321 Relay to Permissive Overreaching Transfer Trip
(POTT) Schemes
AG96-19 Applying the SEL-321 Relay to Directional Comparison Unblocking
(DCUB) Schemes
The major differences are how the optoisolated input settings and the trip settings are made. The
following explanations describe these differences.
Optoisolated Input Settings Differences Between the SEL-321 and SEL-351 Relays
The SEL-351 Relay does not have optoisolated input settings like the SEL-321 Relay. Rather, the
optoisolated inputs of the SEL-351 Relay are available because Relay Word bits and are used in
SELOGIC Control Equations. The following optoisolated input setting example is for a Permissive
Overreaching Transfer Trip (POTT) scheme.
SEL-321 Relay SEL-351 Relay
IN2 = PT PT1 = IN2 (received permissive trip)
In the above SEL-351 Relay setting example, Relay Word bit IN2 is set in the PT1 SELOGIC
Control Equation. Optoisolated input IN2 is wired to a communications equipment receiver output
contact. Relay Word bit IN2 can also be used in other SELOGIC Control Equation in the
Courtesy of NationalSwitchgear.com