Schweitzer Engineering SEL-351P, Quick Start Manual

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Date Code 990215 Setting Negative-Sequence Overcurrent Elements F-3
SEL-351P Manual Técnico
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 - 351P can be inserted as the feeder relay in this example. Note that the overcurrent
element labels in the example are not the same as the labels of the corresponding SEL - 351P
overcurrent elements.
Coordination Guidelines
1. Start with the furthest downstream negative-sequence overcurrent element (e.g., distribution
feeder relay in a substation).
2. Identify the phase overcurrent device (e.g., line recloser, fuse) downstream from the
negative-sequence overcurrent element that is of greatest concern for coordination. This is
usually the phase overcurrent device with the longest clearing time.
3. Consider the negative-sequence overcurrent element as an “equivalent” phase overcurrent
element. Derive pickup, time dial (lever), curve type, or time-delay settings for this
“equivalent” element to coordinate with the downstream phase overcurrent device, as any
phase coordination would be performed. Load considerations can be disregarded when
deriving the “equivalent” phase overcurrent element settings.
4. Multiply the “equivalent” phase overcurrent element pickup setting by 3 to convert it to
the negative-sequence overcurrent element pickup setting in terms of 3I
2
current.
Negative-
sequence
overcurrent
element
pickup
}
= ⋅
3 (“equivalent” phase overcurrent element
pickup)
Any time dial (lever), curve type, or time delay calculated for the “equivalent” phase
overcurrent element is also used for the negative-sequence overcurrent element with no
conversion factor applied.
5. Set the next upstream negative-sequence overcurrent element to coordinate with the first
downstream negative-sequence overcurrent element and so on. Again, coordination is not
influenced by load considerations.
Coordination Example
In Figure APPENDIX F: .2, the phase and negative-sequence overcurrent elements of the feeder
relay (51F and 51QF, respectively) must coordinate with the phase overcurrent element of the
line recloser (51R).