F.7
Date Code 20110408 Instruction Manual SEL-551 Relay
Setting Negative-Sequence Overcurrent Elements
Other Negative-Sequence Overcurrent Element References
Ground Coordination
Concerns
If the downstream protective device includes ground overcurrent elements, in
addition to phase overcurrent elements, there should be no need to check the
coordination between the ground overcurrent elements and the upstream
negative-sequence overcurrent elements. The downstream phase overcurrent
element, whether it operates faster or slower than its complementary ground
overcurrent element, will operate faster than the upstream negative-sequence
overcurrent element for all faults, including those that involve ground.
Other Negative-Sequence Overcurrent Element
References
A. F. Elneweihi, E. O. Schweitzer, M. W. Feltis, “Negative-Sequence
Overcurrent Element Application and Coordination in Distribution
Protection,” IEEE Transactions on Power Delivery, Volume 8, Number 3,
July 1993, pp. 915–924.
This IEEE paper is the source of the coordination guidelines and example
given in this appendix. The paper also contains analyses of system unbalances
and faults and the negative-sequence current generated by such conditions.
A. F. Elneweihi, “Useful Applications for Negative-Sequence Overcurrent
Relaying,” 22nd Annual Western Protective Relay Conference, Spokane,
Washington, October 24–26, 1995.
This conference paper gives many good application examples for negative-
sequence overcurrent elements. The focus is on the transmission system,
where negative-sequence overcurrent elements provide better sensitivity than
zero-sequence overcurrent elements in detecting some single-line-to-ground
faults.
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