3-8 Overcurrent, Voltage, Synchronism Check, Frequency, and Power Elements Date Code 20001006
SEL-351 Instruction Manual
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 through 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 through 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):
50AB1 = 1 (logical 1), if I
AB
> pickup setting 50PP1P
= 0 (logical 0), if I
AB
≤ pickup setting 50PP1P
50BC1 = 1 (logical 1), if I
BC
> pickup setting 50PP1P
= 0 (logical 0), if I
BC
≤ pickup setting 50PP1P
50CA1 = 1 (logical 1), if I
CA
> pickup setting 50PP1P
= 0 (logical 0), if I
CA
≤ pickup setting 50PP1P
Pickup and Reset Time Curves
See Figure 3.5 and Figure 3.6.
Neutral Ground Instantaneous/Definite-Time Overcurrent Elements
Four levels of neutral ground instantaneous/definite-time overcurrent elements are available. Two
additional levels of neutral ground instantaneous overcurrent elements (Levels 5 and 6) are also
available. The different levels are enabled with the E50N enable setting, as shown in Figure 3.8
and Figure 3.9.
Level 2 element 67N2S in Figure 3.8 is used in directional comparison blocking schemes (see
Directional Comparison Blocking (DCB) Logic in Section 5: Trip and Target Logic). All the
other neutral ground instantaneous/definite-time overcurrent elements are available for use in any
tripping or control scheme.
Courtesy of NationalSwitchgear.com
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