Schweitzer Engineering Laboratories SEL-351 - Pickup and Reset Time Curves

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 SELOGIC 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
Courtesy of NationalSwitchgear.com