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4.56
SEL-351-5, -6, -7 Relay
Instruction Manual
Date Code 20070117
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Directional Control Settings
For situations where zero-sequence source isolation can occur (e.g., by
opening a circuit breaker) and result in possible mutual coupling problems for
the zero-sequence voltage-polarized and channel IN current-polarized
directional elements, SEL
OGIC
control equation setting E32IV should be
deasserted to logical 0. In this example, connect a circuit breaker auxiliary
contact from the isolating circuit breaker to the SEL-351:
E32IV =
IN106
(52a connected to optoisolated input
IN106
)
Almost any desired control can be set in SEL
OGIC
control equation setting
E32IV.
Ungrounded/High-Impedance Grounded System Considerations for
Setting E32IV
On ungrounded/high-impedance grounded systems (when setting ORDER =
U), phase-to-phase or unbalanced three-phase faults can cause the
ungrounded/high-impedance grounded element to operate on false quantities.
To prevent this situation, SEL
OGIC
setting E32IV may be used as follows:
E32IV =
V1GOOD * !32QE
The V1GOOD Relay Word bit (see
) deasserts during a three-phase
fault, and the 32QE Relay Word bit (see
) asserts during a phase-to-
phase fault. If either one of these occur, the E32IV setting evaluates to
logical 0, and the ungrounded/high-impedance grounded directional element
is blocked (see
When a switch or breaker closes, the poles can close sequentially (not at the
same time), creating a momentary current unbalance condition. To avoid any
possible operation of the ungrounded/ high-impedance grounded element for
this momentary current unbalance condition, set 3PO (three-pole open
condition; see
) in SEL
OGIC
setting E32IV as follows:
E32IV =
… + !3PO
(= … + NOT[3PO])
The 3PO dropout time (setting 3POD) provides the extended blocking (3PO =
logical 1; !3PO = logical 0) for this momentary current unbalance condition.
Содержание SEL-351-5
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