Schweitzer Engineering Laboratories SEL-351 - Convert Equivalent Phase Overcurrent Element Settings to Negative-Sequence Overcurrent Element Settings (Guideline 4

Date Code 20001006 Setting Negative-Sequence Overcurrent Elements F-5
SEL-351 Instruction Manual
Figure F.4: Phase-to-Phase Fault Coordination
51EP: pickup = 300 A (below max. feeder load, I
F
)
Considerable improvement in sensitivity and speed of operation for phase-to-phase faults is
achieved with the 51EP element. The 51EP element pickup of 300 A has twice the sensitivity of
the 51F element pickup of 600 A. The 51EP element speed of operation for phase-to-phase faults
below about 2000 A is faster than that for the 51F element.
Convert “Equivalent” Phase Overcurrent Element Settings to Negative-
Sequence Overcurrent Element Settings (Guideline 4)
The “equivalent” phase overcurrent element (51EP element in Figure F.4) converts to true
negative-sequence overcurrent element settings (51QF in Figure F.5) by applying the equation
given in Guideline 4. The time dial (lever) and curve type of the element remain the same (if the
element is a definite-time element, the time delay remains the same).
Courtesy of NationalSwitchgear.com