5-14 Trip and Target Logic Date Code 20001006
SEL-351 Instruction Manual
SEL-351 Relay. See Optoisolated Inputs in Section 7: Inputs, Outputs, Timers, and Other
Control Logic for more information on optoisolated inputs.
Trip Settings Differences Between the SEL-321 and SEL-351 Relays
Some of the SELOGIC Control Equation trip settings of the SEL-321 and SEL-351 Relays are not
operationally different, just labeled differently. The correspondence is:
SEL-321 Relay SEL-351 Relay
MTCS TRCOMM (Communications-Assisted Trip Conditions)
MTO TRSOTF (Switch-Onto-Fault Trip Conditions)
MTU TR (Unconditional or Other Trip Conditions)
The SEL-321 Relay handles trip unlatching with setting TULO. The SEL-351 Relay handles trip
unlatching with SELOGIC Control Equation setting ULTR.
The SEL-321 Relay has single-pole trip logic. The SEL-351 Relay does not have single-pole trip
logic.
PERMISSIVE OVERREACHING TRANSFER TRIP (POTT) LOGIC
Enable the POTT logic by setting ECOMM = POTT. The POTT logic in Figure 5.6 is also
enabled for directional comparison unblocking schemes (ECOMM = DCUB1 or
ECOMM = DCUB2). The POTT logic performs the following tasks:
• Keys communication equipment to send permissive trip when any element included in the
SELOGIC Control Equation communications-assisted trip equation TRCOMM asserts
and the current reversal logic is not asserted.
• Prevents keying and tripping by the POTT logic following a current reversal.
• Echoes the received permissive signal to the remote terminal.
• Prevents channel lockup during echo and test.
• Provides a secure means of tripping for weak- and/or zero-infeed line terminals.
Use Existing SEL-321 Relay POTT Application Guide for the SEL-351 Relay
Use the existing SEL-321 Relay POTT application guide (AG95-29) to help set up the SEL-351
Relay in a POTT scheme (see preceding subsection Communications-Assisted Trip Logic –
General Overview for more setting comparison information on the SEL-321/SEL-351 Relays).
External Inputs
See Optoisolated Inputs in Section 7: Inputs, Outputs, Timers, and Other Control Logic for
more information on optoisolated inputs.
Courtesy of NationalSwitchgear.com
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