Schweitzer Engineering Laboratories SEL-700G Series, Инструкция по эксплуатации

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4.128
SEL-700G Relay Instruction Manual Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
The 50QRP setting (3I
2
current value) is the pickup for the reverse fault
detector 50QR of the negative-sequence voltage-polarized directional
elements (see Figure 4.74). Ideally, the setting is above normal load unbalance
and below the lowest expected negative-sequence current magnitude for
unbalanced reverse faults.
I
f enable setting EDIR := AUTO, the settings 50QFP and 50QRP are set
automatically at:
50QFP = 0.50 A secondary (5 A nominal phase current inputs,
IA
,
IB
,
IC
)
50QRP = 0.25 A secondary (5 A nominal phase current inputs,
IA
,
IB
,
IC
)
50QFP = 0.10 A secondary (1 A nominal phase current inputs,
IA
,
IB
,
IC
)
50QRP = 0.05 A secondary (1 A nominal phase current inputs,
IA
,
IB
,
IC
)
a2—Positive-Sequence Current Restraint Factor, I
2
/I
1
.
The a2 factor
(refer to Figure 4.74) increases the security of the negative-sequence voltage-
polarized directional elements. It keeps the elements from operating for
negative-sequence current (system unbalance), which circulates as a result of
line asymmetries, CT saturation during three-phase faults, etc.
If enable setting EDIR := AUTO, setting a2 is set automatically at:
a2 = 0.1
For setting a2 = 0.1, the negative-sequence current (I
2
) magnitude has to be
greater than 1/10 of the positive-sequence current (I
1
) magnitude in order for
the negative-sequence voltage-polarized directional elements to be enabled
(|I
2
| > 0.1 • |I
1
|).
k2—Zero-Sequence Current Restraint Factor, I
2
/I
0
.
Note the internal
enable logic outputs in Figure 4.74:
The k2 factor is applied to internal enable DIRQGE. The negative-sequence
current (I
2
) magnitude has to be greater than the zero-sequence current (I
0
)
magnitude multiplied by k2 in order for the DIRQGE internal enable (and
following negative-sequence voltage-polarized directional element in
Figure 4.77) to be enabled:
This check ensures that the relay uses the most robust analog quantities in
making directional decisions for the neutral-ground and residual-ground
overcurrent elements.
The zero-sequence current (I
0
), referred to in the previous application of the
k2 factor, is from the residual current (I
G
), which is derived from phase
currents I
A
, I
B
, and I
C
:
DIRQE internal enable for the negative-sequence voltage-polarized
directional element that controls the negative-sequence and
phase overcurrent elements
DIRQGE internal enable for the negative-sequence voltage-polarized
directional element that controls the residual-ground
overcurrent elements
I
0
= I
G
/3 3I
0
= I
G
= I
A
+ I
B
+ I
C
I
2
k2 I
0
•
