3-30
Distance, Overcurrent, Voltage,
Date Code 20011205
and Synchronism Check Elements
SEL-311B Instruction Manual
Accuracy
Pickup:
±
0.05 A secondary and
±
3% of setting (5 A nominal phase current inputs, IA, IB, IC)
±
0.01 A secondary and
±
3% of setting (1 A nominal phase current inputs, IA, IB, IC)
Curve Timing:
±
1.50 cycles and
±
4% of curve time for currents between (and including) 2 and
30 multiples of pickup
Negative-Sequence Time-Overcurrent Element
To understand the operation of Figure 3.20, follow the explanation given for Figure 3.18 in the
preceding
Phase Time-Overcurrent Elements
subsection, substituting negative-sequence current
3I
2
[3I
2
= I
A
+ a
2
• I
B
+ a • I
C
(ABC rotation), 3I
2
= I
A
+ a
2
• I
C
+ a • I
B
(ACB rotation), where
a = 1
Ð
120° and a
2
= 1
Ð
-120°] for maximum phase current I
ABC
and like settings and Relay
Word bits.
Figure 3.20: Negative-Sequence Time-Overcurrent Element 51QT
IMPORTANT
: See
Appendix F
for information on setting negative-sequence overcurrent
elements.
Summary of Contents for SEL-311B
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