Sel 411L - Table 3.8 87 LQ Negative-Sequence Differential Element Relay Word Bits; Table 3.9 87 LG Zero-Sequence Differential Element Settings

P.3.39
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
87L Differential Elements
When you use channels that are guaranteed to be symmetrical (for example,
direct fiber), channel asymmetry is not a concern and you can make this
setting more sensitive. Also, by applying external time-based synchronization
to asymmetrical channels, you reduce the danger of synchronization errors
and can use lower blocking angle values. Note that the time fallback logic that
responds to the loss or degradation of the time sources you use will force the
extended security settings. You may therefore set the blocking angle setting in
the extended security mode, 87LQAS, conservatively, while setting the
regular security blocking angle setting, 87LQA, to be more sensitive.
Note that the negative-sequence network is typically very homogeneous; the
Alpha Plane angle under internal faults is very close to zero. Therefore, a
conservative value for the 87LQA or 87LQAS setting typically does not
impact dependability of the 87LQ element.
87LG Zero-Sequence Differential Element
This section describes the application without in-line transformers
(87XFMR = N). The zero-sequence differential element is unavailable in
applications with in-line transformers.
As Figure 3.23 shows, the zero-sequence differential element applies the basic
settings of the Alpha Plane characteristic (pickup, radius, and blocking angle,
see Table 3.9) to its zero-sequence operating quantities (magnitude of the
differential current, ratio, and angle of the Alpha Plane, see Table 3.10).
The logic, settings, operating quantities, and Relay Word bits are virtually
identical between the phase- and zero-sequence differential elements. Refer to
87LP Phase Differential Elements for detailed explanation.
Table 3.8 87LQ Negative-Sequence Differential Element Relay Word Bits
Name Description
87LQ Negative-sequence differential element operated
87L50Q Overcurrent supervision of the negative-sequence differential element
picked up
Table 3.9 87LG Zero-Sequence Differential Element Settings
Setting Description Range Default
87LGP Pickup threshold of the zero-sequence differen-
tial element in the normal security mode (pu)
OFF, 0.1–2 0.25
87LGR Radius of the zero-sequence differential ele-
ment in the normal security mode
1.2–8 6
87LGA Blocking angle of the zero-sequence differential
element in the normal security mode (deg)
90–270 195
87LGPS
a
a
Advanced settings (EADVS = Y).
Pickup threshold of the zero-sequence differen-
tial element in the extended security mode (pu)
OFF, 0.1–2 0.3
87LGRS
a
Radius of the zero-sequence differential ele-
ment in the extended security mode
1.2–8 7.2
87LGAS
a
Blocking angle of the zero-sequence differential
element in the extended security mode (deg)
90–270 234