Schweitzer Engineering Laboratories SEL-351 - Accuracy; Logic Outputs (51 PT Element Example)

3-18 Overcurrent, Voltage, Synchronism Check, Frequency, and Power Elements Date Code 20001006
SEL-351 Instruction Manual
Figure 3.14: Phase Time-Overcurrent Element 51PT (With Directional Control Option)
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)
Curve Timing: ±1.50 cycles and ±4% of curve time for currents between (and including)
2 and 30 multiples of pickup
Logic Outputs (51PT Element Example)
The resultant logic outputs in Figure 3.14 are the following Relay Word bits:
Table 3.3: Phase Time-Overcurrent Element (Maximum Phase) Logic Outputs
Relay Word Bit Definition/ Indication Application
51P Maximum phase current, I
P
, is
greater than phase time-
overcurrent element pickup setting
51PP.
Element pickup testing or other
control applications. See Trip
Logic in Section 5: Trip and
Target Logic.
51PT Phase time-overcurrent element is
timed out on its curve.
Tripping and other control
applications. See Trip Logic in
Section 5: Trip and Target Logic.
51PR Phase time-overcurrent element is
fully reset.
Element reset testing or other
control applications.
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