3.14
SEL-351A Relay Instruction Manual Date Code 20080213
Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Instantaneous/Definite-Time Overcurrent Elements
To understand the operation of Figure 3.12 and Figure 3.13, follow the
explanation given for Figure 3.1, Figure 3.2, and Figure 3.3 in Phase
Instantaneous/Definite-Time Overcurrent Elements on page 3.1, substituting
negative-sequence current:
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)
for phase currents and substituting like settings and Relay Word bits.
Settings Ranges
Setting range for pickup settings 50Q1P–50Q6P:
0.25–100.00 A secondary (5 A nominal phase current inputs, IA, IB, IC)
0.05–20.00 A secondary (1 A nominal phase current inputs, IA, IB, IC)
Setting range for definite-time settings 67Q1D–67Q4D:
0.00–16000.00 cycles, in 0.25-cycle steps
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)
Timer:
±0.25 cycles and ±0.1% of setting
Transient Overreach:
±5% of setting
Pickup and Reset Time Curves
See Figure 3.5 and Figure 3.6.
where:
a = 1 ∠ 120°
a
2
=1 ∠ –120°
Courtesy of NationalSwitchgear.com
To Next Page
Loading...