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4.3
Date Code 20080213
Instruction Manual
SEL-351A Relay
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Loss-of-Potential Logic (Not in the SEL-351A-1)
Setting ELOP = Y
Additionally, if setting ELOP = Y and a loss-of-potential condition occurs
(Relay Word bit LOP asserts to logical 1), overcurrent elements set direction
forward (see
Note 2
) are enabled (see
,
, and
). These direction forward overcurrent elements effectively
become nondirectional and provide overcurrent protection during a loss-of-
potential condition.
As detailed previously, voltage-based directional elements are disabled during
a loss-of-potential condition. Thus, the overcurrent elements controlled by
these voltage-based directional elements are also disabled. However, this
disable condition is overridden for the overcurrent elements set direction
forward if setting ELOP = Y.
NOTE 2:
When global setting VSCONN = 3V0, the various ground-
directional elements that rely on zero-sequence voltage quantities (ORDER
settings V, S, P, and U) are not affected by a loss-of-potential condition on
relay inputs
VA
,
VB
, and
VC
, because these elements use the 3V
0
zero-sequence
voltage that comes directly from voltage input
VS
, rather than the zero-
sequence voltage calculated from voltage inputs
VA
,
VB
, and
VC
(wye-
connected PTs). This difference is shown in
where Relay Word bit 3V0 is combined with Relay Word bits 32NE and 32VE
to create a block signal for the loss-of-potential signal. When LOP is asserted
and setting ELOP = Y1, the relay will not force an enable of the ground
elements that are set direction-forward when Relay Word bit 3V0 is asserted
(= logical 1) and one of the zero-sequence voltage-polarized ground
directional element enables (32VE or 32NE) is asserted. Refer to
Voltage Input Configuration on page 9.36
Setting ELOP = N
If setting ELOP = N, the loss-of-potential logic still operates (Relay Word bit
LOP asserts to logical 1 for a loss-of-potential condition) but does not disable
any voltage-based directional elements (as occurs with ELOP = Y or Y1) or
enable overcurrent elements set direction forward (as occurs with ELOP = Y).
Содержание SEL-351A
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