Date Code 20001006
Overcurrent, Voltage, Synchronism Check, Frequency, and Power Elements
3-7
SEL-351 Instruction Manual
Pickup and Reset Time Curves
Figure 3.5 and Figure 3.6 show pickup and reset time curves applicable to all nondirectional
instantaneous overcurrent elements in the SEL-351 Relay (60 Hz or 50 Hz relays). These times do
not include output contact operating time and , thus, are accurate for determining element operation
time for use in internal SEL
OGIC
Control Equations. Output contact pickup/dropout time is 4 ms
(0.25 cycle for a 60 Hz relay; 0.20 cycle for a 50 Hz relay).
If instantaneous overcurrent elements are made directional, the pickup time curve in Figure 3.5 is
adjusted as follows:
multiples of pickup setting
≤
4: add 0.25 cycle
multiples of pickup setting > 4: add 0.50 cycle
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.2
2
3
4
5
6
7
8
9
10
Applied Current (Multiples of Pickup Setting)
Pickup Time (Cycles)
Maximum
Minimum
Figure 3.5: SEL-351 Relay Nondirectional Instantaneous Overcurrent Element Pickup Time
Curve
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.2
2
3
4
5
6
7
8
9
10
Applied Current (Multiples of Pickup Setting)
Reset Time (Cycles)
Maximum
Minimum
Figure 3.6: SEL-351 Relay Nondirectional Instantaneous Overcurrent Element Reset Time
Curve
Summary of Contents for SEL-351
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