4-2
Loss-of-Potential, CCVT Transient Detection,
Date Code 20011205
Load-Encroachment, and Directional Element Logic
SEL-311A Instruction Manual
Loss-of-potential is declared (Relay Word bit LOP = logical 1) when a 10 percent drop in V
1
is
detected, with no corresponding change in I
1
or I
0
. If the LOP condition persists for 60 cycles, it
latches in. LOP resets (Relay Word bit LOP = logical 0) when V
1
returns above 50 V secondary
and V
0
is less than 5 V secondary.
The loss-of-potential enable setting, ELOP, does not enable or disable the LOP logic. It just
routes the LOP Relay Word bit to different logic, as shown in Figure 4.1 and explained in the
remainder of this subsection.
Note that ILOP disables all distance elements (Figure 3.4 through Figure 3.7).
Setting ELOP = Y or Y1
If setting ELOP = Y or Y1 and a loss-of-potential condition occurs (Relay Word bit LOP asserts
to logical 1), negative-sequence voltage-polarized, zero-sequence voltage-polarized, and positive-
sequence voltage-polarized directional elements, plus all distance elements, are disabled by relay
word bit ILOP (see Figure 4.9, Figure 4.10, Figure 4.14, Figure 4.15, and Figure 3.4 through
Figure 3.7). The loss-of-potential condition makes these voltage-polarized directional elements
and distance elements unreliable. Thus, they are disabled. The overcurrent elements controlled
by these voltage-polarized directional elements are disabled also (unless overridden by conditions
explained in the following
Setting ELOP = Y
discussion).
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 are enabled (see Figure 4.12).
These direction forward overcurrent elements effectively become nondirectional and provide
overcurrent protection during a loss-of-potential condition.
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-polarized directional
elements or any distance elements (as occurs with ELOP = Y or Y1), nor does it enable
overcurrent elements set direction forward (as occurs with ELOP = Y).
CCVT T
RANSIENT
D
ETECTION
L
OGIC
The SEL-311A detects CCVT transients that may cause Zone 1 distance overreach. If CCVT
transient blocking is enabled (setting ECCVT = Y), and the relay detects a high SIR during a
Zone 1 fault, the relay delays tripping for up to 1.5 cycles, allowing the CCVT to stabilize.
User settings are not required. The relay automatically adapts to different system SIR conditions
by monitoring voltage and current.
For close-in faults on systems with high SIRs, the SEL-311A Relay uses distance-calculation
smoothness detection to override the tripping delay caused by low voltage and low current.
Distance elements operate without significant delay for close-in faults.
Содержание SEL-311A
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