Date Code 20011026
Applications
5-13
SEL-321/321-1 Instruction Manual
Set a2 to some value less than the calculated values for our example a2 is selected for 0.07.
Z2F = 0.77
0.77
0.77
0.77
50QF = 0.5
0.5
0.5
0.5
Z2R = 5.45
5.45
5.45
5.45
50QR = 0.5
0.5
0.5
0.5
a2 = 0.07
0.07
0.07
0.07
- Relay Elements and Other Settings Affected
32QF and 32QR elements. All ground distance elements and all directionally controlled residual
and negative-sequence overcurrent elements.
Phase Time-Overcurrent Element Setting
The phase time-overcurrent element is not required for this application. The phase time-
overcurrent element is disabled by setting E51P = N.
E51P = NNNN
- Relay Elements and Other Settings Affected
Relay elements 51PT and 51PP depend on the 51PP, 51PC, 51PTD, 51PRS, and 51PTC settings.
Residual Overcurrent Settings
Residual Time-Overcurrent Settings
The residual time-overcurrent element provides current dependent, time delayed clearance of
faults along the protected line and provides backup protection for remote terminals. Because the
measure of residual current varies with system switching configuration, fault location, and fault
resistance, a complete fault study is necessary to determine the minimum pickup setting,
appropriate time dial, and curve characteristic. When the element is directionally controlled,
consider only faults in front of the line terminal for coordinating purposes.
For the relay at Breaker 3, a single line-to-ground fault at Bus C with Line 1 or 4 removed
dictates the sensitivity required for the residual time-overcurrent pickup. The residual current
magnitude for this fault is 308 A primary. To allow for ground fault resistance, a value of 50%
of 308 A is selected as the residual time-overcurrent element pickup. The pickup (51NP), time
dial (51NTD), and curve family (51NC) selections are assumed to coordinate with the remaining
residual time-overcurrent elements of the example system.
Instantaneous/Definite-Time Residual Overcurrent Settings
The residual instantaneous/ definite-time overcurrent elements are not required for this
application. The residual overcurrent elements are disabled by setting E50N = N.
Summary of Contents for SEL-321
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