Date Code 990430
Overcurrent, Voltage, Synchronism Check, and Frequency Elements
3-27
SEL-351P Manual Técnico
Negative-Sequence Time-Overcurrent Element
Figure SECTION 3: .20:
Negative-Sequence Time-Overcurrent Element 51QT (with
Directional Control Option)
IMPORTANT
: See
Appendix F: Setting Negative-Sequence Overcurrent Elements
for
information on setting negative-sequence overcurrent elements.
To understand the operation of Figure SECTION 3: .20, follow the explanation given for
Figure SECTION 3: .14 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
∠
120
°
and a
2
= 1
∠
-120
°
] for maximum
phase current I
P
and like settings and Relay Word bits.
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