Schweitzer Engineering SEL-351P - Negative-Sequence Instantaneous;Definite-Time Overcurrent Elements; Accuracy; Pickup and Reset Time Curves; Settings Ranges

3-14 Overcurrent, Voltage, Synchronism Check, and Frequency Elements Date Code 990430
SEL-351P Manual Técnico
Negative-Sequence Instantaneous/Definite-Time Overcurrent Elements
IMPORTANT: See Appendix F: Setting Negative-Sequence Overcurrent Elements for
information on setting negative-sequence overcurrent elements.
Four levels of negative-sequence instantaneous/definite-time overcurrent elements are available.
Two additional levels of negative-sequence instantaneous overcurrent elements (Levels 5 and 6)
are also available. The different levels are enabled with the E50Q enable setting, as shown in
Figure SECTION 3: .12 and Figure SECTION 3: .13.
Level 2 element 67Q2S in
Figure SECTION 3: .12 is used in directional comparison blocking
schemes (see Directional Comparison Blocking (DCB) Logic in Section 5: Trip and Target
Logic). All the other negative-sequence instantaneous/definite-time overcurrent elements are
available for use in any tripping or control scheme.
To understand the operation of
Figure SECTION 3: .12 and Figure SECTION 3: .13, follow the
explanation given for
Figure SECTION 3: .1, Figure SECTION 3: .2, and Figure SECTION 3:
.3 in the preceding Phase Instantaneous/Definite-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 phase
currents and substituting like settings and Relay Word bits.
Settings Ranges
Setting range for pickup settings 50Q1P through 50Q6P:
0.05 - 20.00 A secondary (1 A nominal phase current inputs, IA, IB, IC)
Setting range for definite-time settings 67Q1D through 67Q4D:
0.00 - 16000.00 cycles, in 0.25-cycle steps
Setting range for definite-time setting 67Q2SD (used in DCB logic):
0.00 - 60.00 cycles, in 0.25-cycle steps
Accuracy
Pickup: ±0.01 A secondary and ±3% of setting (1 A nominal phase current inputs, IA, IB, IC)
Timer: ±0.25 cycles and ±0.1% of setting
Transient Overreach: ±5% of setting
Pickup and Reset Time Curves
See
Figure SECTION 3: .5 and Figure SECTION 3: .6.