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Power Automation and Protection Division
NOTE:
4.11
Phase Comparison Count Logic (CNT)
This setting provides a choice between sensitivity and increased security. The options are:
• 1CNT — Only one 4 msec, trip comparison (output of COMP-AND) is required to
• 2 CNT — If the coincidence at the output of COMP-AND (Figure 3-7) is only 4 to 6
For more security set CNT = 2 CNT.
4.12
Trip Arm (TARMT)
For terminals in which the fault current disappears too fast, for example close to an AC-DC in-
terconnection, it is necessary to stretch the duration of TARM to ensure the tripping of the other
terminal.
The timer may be chosen to be:
• 0
• 150
Notice that stretching TARM implies that the trip output will be energized longer.
NOTE:
4.13
Low Set Phase Unit (IPL)
The low set overcurrent units perform the supervision of stub bus function tripping undesirably
under line energization.
The phase (IPL) unit should be set at 1.5 times the net line charging current, but must be at
least .5 A. Net line charging current is herein defined as: the steady state net single-end line
charging phase current, as measured under balanced conditions (all local poles closed and all
remote poles open).
"Net" line charging indicates the distributed capacitive current minus the line-connected shunt
reactor current (if any), since line-connected shunt reactors are within the zone of protection of
the phase comparison and tend to cancel the capacitive current.
4.14
High Set Phase Overcurrent Unit (IPH)
This unit is provided in the REL 352 system to supplement the phase comparison protection by
providing a non-pilot direct trip capability for high current internal faults. The IPH unit should be
set above the maximum expected external fault current with a security margin.
On lines which do not contain series capacitors, the IPH unit should be set for 1.25 times the
maximum through current for an external three phase fault.
These high set overcurrent units are only directional when the distance back-up function is in-
cluded in the REL 352 system. IPH is supervised by FDOP for all phase subsystems.
REL 352 Version 1.00
For channels other than Power Line Carrier (i.e., Audio Tone) this setting
should be set to OUT.
trip the system.
milliseconds long a second coincidence greater than 4 milliseconds is
required within 25 msec (for FSK PLC) or 40 msc (for ON-OF PLC). If
this output is longer than 6 milliseconds, no second comparison is re-
quired.
— No pulse stretch
— TARM will be stretched 150 milliseconds.
For most of the applications this setting should be "0".
I.L. 40-201.9
5
5-5
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