F-2 Setting Negative-Sequence Overcurrent Elements Date Code 20001006
SEL-351 Instruction Manual
To avoid having negative-sequence time-overcurrent element 51QT with such low time-dial
settings trip for this transient negative-sequence current condition, make settings similar to the
following:
SV6PU = 1.50 cycles (minimum response time; transient condition lasts
less than 1.5 cycles)
SV6 = 51Q (run pickup of negative-sequence time-overcurrent
element 51QT through SELOGIC Control Equation
variable timer SV6)
TR = ..+51QT*SV6T+.. (trip conditions; SV6T is the output of the SELOGIC
Control Equation variable timer SV6)
Figure F.1: Minimum Response Time Added to a Negative-Sequence Time-Overcurrent
Element 51QT
Continue reading in Coordinating Negative-Sequence Overcurrent Elements in this appendix for
guidelines on coordinating negative-sequence time-overcurrent elements and a following
coordination example.
COORDINATING NEGATIVE-SEQUENCE OVERCURRENT ELEMENTS
The following coordination guidelines and example assume that the negative-sequence overcurrent
elements operate on 3I
2
magnitude negative-sequence current and that the power system is radial.
The negative-sequence overcurrent elements in the SEL-351 Relay operate on 3I
2
magnitude
negative-sequence current.
The coordination example is a generic example that can be used with any relay containing
negative-sequence overcurrent elements that operate on 3I
2
magnitude negative-sequence current.
The SEL-351 Relay can be inserted as the feeder relay in this example. Note that the overcurrent
Courtesy of NationalSwitchgear.com
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