Schweitzer Engineering SEL-351P - Loss-Of-Potential Logic; Section 4: Loss-Of-Potential, Load Encroachment, and Directional Element Logic

Date Code 990430 Loss-of-Potential, Load Encroachment, and Directional Element Logic 4-1
SEL-351P Manual Técnico
SECTION 4: LOSS-OF-POTENTIAL, LOAD ENCROACHMENT,
AND DIRECTIONAL ELEMENT LOGIC
L OSS - OF -P OTENTIAL L OGIC
The loss-of-potential (LOP) logic operates as shown in Figure SECTION 4: .1.
4.13, and 4.19
4.11, 4.17, and 4.18
LOP
to Figures 4.12,
to Figure 5.6
to Figures 4.9, 4.10,
3PO
Loss-of-
Potential
Logic
DWG: M351R094
Rela
y
Word
Bit
V
1
, I
1
, I
0
V
0
(from Figure 5.3)
Setting
3PVOLT = Y
ELOP=Y OR Y1
ELOP=Y1
ELOP=Y
Relay
Word
Bit
Figure SECTION 4: .1: Loss-of-Potential Logic
Inputs into the LOP logic are:
3PO three-pole open condition (indicates circuit breaker open condition
see Figure 5.3)
V
1
positive-sequence voltage (V secondary)
I
1
positive-sequence current (A secondary)
V
0
zero-sequence voltage (V secondary)
I
0
zero-sequence current (A secondary)
V
2
negative-sequence voltage (V secondary)
The circuit breaker has to be closed (Relay Word bit 3PO = logical 0) for the LOP logic to
operate. The EZ global setting “True three-phase voltage connected (Y/N)” = Y also has to be
made in order for the LOP logic to operate (corresponding “regular” global setting
3PVOLT = Y). Even if the LOP logic is not used (i. e., no directional overcurrent elements are
used), setting 3PVOLT = Y should still be made (SET G command) if true three-phase voltage is
connected to the SEL-351P.
Loss-of-potential is declared (Relay Word bit LOP = logical 1) when a 10% 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.