5-14 Trip and Target Logic Date Code 20010625
SEL-311L Instruction Manual
relay continues to see zero voltage. The directional elements have no voltage for reference and
cannot operate. In this case, the instantaneous overcurrent element in the SOTF trip logic should
be nondirectional.
COMMUNICATIONS-ASSISTED TRIP LOGIC—GENERAL OVERVIEW
The SEL-311L Relay includes communications-assisted tripping schemes that provide unit-
protection for transmission lines with the help of communications. No external coordination
devices are required.
Figure 5.6: Communications-Assisted Tripping Scheme
Refer to Figure 5.6 and the top half of Figure 5.4.
The six available tripping schemes are:
v
Direct Transfer Trip (DTT)
v
Direct Underreaching Transfer Trip (DUTT)
v
Permissive Overreaching Transfer Trip (POTT)
v
Permissive Underreaching Transfer Trip (PUTT)
v
Directional Comparison Unblocking (DCUB)
v
Directional Comparison Blocking (DCB)
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