Date Code 20001006 Setting Negative-Sequence Overcurrent Elements F-3
SEL-351 Instruction Manual
element labels in the example are not the same as the labels of the corresponding SEL-351 Relay
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 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).
Figure F.2: Distribution Feeder Protective Devices
Courtesy of NationalSwitchgear.com
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