Schweitzer Engineering SEL-351P - Negative-Sequence Time-Overcurrent Element

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.