Schweitzer Engineering Laboratories SEL-321 - MTCS (Communications-Scheme Trip Variable); MTO (Switch-Onto-Fault Trip Variable); Unlatch Logic Selections

Date Code 20011026 Specifications 2-39
SEL-321/321-1 Instruction Manual
MTO (Switch-Onto-Fault Trip Variable)
Include more-sensitive elements for instantaneous and sensitive tripping when the breaker is first
closed onto a fault. For example, to trip instantaneously on Zone 2 elements:
MTO = M2P + Z2G
MTCS (Communications-Scheme Trip Variable)
Set the combination of overreaching elements which can trip only if the communications logic
permits (on the basis of POTT permission received, for example). If Zone 2 elements are the
desired overreaching elements, then set:
MTCS = M2P + Z2G
Unlatch Logic Selections
This logic deasserts asserted tripping elements.
One of five unlatch options is chosen with the TULO (Trip Unlatch Option) setting:
Option
Setting Description
N TULO = N Time delayed dropout extension
1 TULO = 1 Undercurrent unlatch
2 TULO = 2 Breaker auxiliary unlatch
3 TULO = 3 Requires conditions of Options 1 and 2
4 TULO = 4 Unlatch when input assigned to EXTUL asserts
Supporting Drawings: Figure 2.46 through Figure 2.48.
MULTIPLE SETTING GROUPS
The relay has six independent setting groups. Each group is a complete relay setting.
Select groups by two means: contact inputs or the GROUP command. Inputs assigned to
SS1 - SS3 control changing group settings by control switches. Input functions not assigned
are treated as zero.
Table 2.25 shows what combinations of asserted logic inputs select which group.
Table 2.25: Setting Group Selections
SS1 SS2 SS3 Group Selected
0
1
0
1
0
1
0
1
0
0
1
1
0
0
1
1
0
0
0
0
1
1
1
1
Group designated by the GROUP Command
Group 1
Group 2
Group 3
Group 4
Group 5
Group 6
Group designated by the GROUP Command