2-14 Specifications Date Code 20011026
SEL-321/321-1 Instruction Manual
Switch-Onto-Fault (SOTF) Logic
The SOTF logic permits specified elements to trip for a settable time after the breaker closes.
Specify these elements in the programmable logic variable called MTO.
Tripping by elements in the MTO variable may be enabled two ways: asserting the CLOSE input
or by timing the slowest 52a contact transition period. Select either or both means in the setting
procedure.
This logic is only active following all breaker poles being open.
External Input
Close Signal CLOSE Drive with the close signal to the breaker(s).
52A1 Breaker Aux. Contacts 52A1 Drive with breaker auxiliary contacts. The num-
52A2 ber of inputs depends on the application and
52AA1 whether single- or three-pole tripping is used.
52AA2
52AB1
52AB2
52AC1
52AC2
Settings
Close Enable Delay CLOEND Sets minimum time duration after all currents drop
out, before CLOSE input activates SOTF logic.
52A Enable Delay 52AEND Sets minimum time after all breaker poles open
before activating SOTF logic.
SOTF Time Duration SOTFD Sets how long tripping by elements in MTO is
active following breaker closure.
High-Set Phase O/C Pickup 50H
Logic Output
Switch-Onto-Fault
Logic Enabled SOTFE Enables three-pole tripping by elements in MTO
logic variable.
Supporting Drawing: Figure 2.37.
Loss-of-Potential (LOP) Logic
This logic detects one, two, or three blown potential fuses. The LOP condition blocks all
distance elements. Settings options will either force forward or block the directional decision for
overcurrent elements.
The relay includes advanced loss-of-potential logic. This logic requires no settings other than the
choice of enable settings. The use of advanced loss-of-potential logic is recommended, however
the option to use the original loss-of-potential logic and settings has been retained to maintain
compatibility with previous versions of the relay. Settings ELOP = N or Y use the original loss-
of-potential logic. Settings ELOP = N1, Y1, or Y2 use the advanced loss-of-potential logic. See
Loss-of-Potential (LOP) Enable Setting (ELOP) in Section 5: Applications for a description of
the LOP logic.
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