Date Code 20001006 Trip and Target Logic 5-11
SEL-351 Instruction Manual
COMMUNICATIONS-ASSISTED TRIP LOGIC – GENERAL OVERVIEW
The SEL-351 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 5.4: Communications-Assisted Tripping Scheme
Refer to Figure 5.4 and the top half of Figure 5.1.
The six available tripping schemes are:
• Direct Transfer Trip (DTT)
• Direct Underreaching Transfer Trip (DUTT)
• Permissive Overreaching Transfer Trip (POTT)
• Permissive Underreaching Transfer Trip (PUTT)
• Directional Comparison Unblocking (DCUB)
• Directional Comparison Blocking (DCB)
Enable Setting ECOMM
The POTT, PUTT, DCUB, and DCB tripping schemes are enabled with enable setting ECOMM.
Setting choices are:
ECOMM = N [no communications-assisted trip scheme enabled]
ECOMM = POTT [POTT or PUTT scheme]
ECOMM = DCUB1 [DCUB scheme for two-terminal line (communications from one
remote terminal)]
Courtesy of NationalSwitchgear.com
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