Schweitzer Engineering Laboratories SEL-351A - Figure 3.5 SEL-351 A Nondirectional Instantaneous Overcurrent Element Pickup Time Curve; Figure 3.6 SEL-351 A Nondirectional Instantaneous Overcurrent Element Reset Time Curve

3.7
Date Code 20080213 Instruction Manual SEL-351A Relay
Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Instantaneous/Definite-Time Overcurrent Elements
Figure 3.5 SEL-351A Nondirectional Instantaneous Overcurrent Element
Pickup Time Curve
Figure 3.6 SEL-351A Nondirectional Instantaneous Overcurrent Element
Reset Time Curve
Phase-to-Phase
Instantaneous
Overcurrent Elements
Four levels of phase-to-phase instantaneous overcurrent elements are
available. The different levels are enabled with the E50P enable setting, as
shown in Figure 3.7.
Setting Range
Setting range for pickup settings 50PP1P–50PP4P:
1.00–170.00 A secondary (5 A nominal phase current inputs, IA, IB, IC)
0.20–34.00 A secondary (1 A nominal phase current inputs, IA, IB, IC)
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)
Pickup Operation
The pickup settings for each level (50PP1P–50PP4P) are compared to the
magnitudes of the individual phase-to-phase difference currents I
AB
, I
BC
,
and I
CA
. The logic outputs in Figure 3.7 are the following Relay Word
bits (Level 1 example shown):
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
Applied Current (Multiples of Pickup Setting)
Reset Time (Cycles)
Maximum
Minimum
2
1.5
1
0.5
0
1.2 2 3 4 5 6 7 8 9 10
50AB1 = 1 (logical 1), if I
AB
> pickup setting 50PP1P
= 0 (logical 0), if I
AB
≤ pickup setting 50PP1P
Courtesy of NationalSwitchgear.com