Sel 411L - Table 3.3 87 LP Phase Differential Elements Settings

P.3.32
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
87L Differential Elements
The 87L function contains two comparators: the overcurrent check and the
Alpha Plane check.
The overcurrent supervision comparator checks the magnitude of the phase
differential current, 87IFM, with the pickup setting 87LPP or 87LPPS
( = A, B, C and denotes the phase). The output of this comparator is
available as the 87L50 Relay Word bit. Figure 3.20 presents internal details
of the overcurrent comparator.
The Alpha Plane comparator, as Figure 3.21 illustrates, compares the ratio and
angle of the generalized Alpha Plane (see 87L Theory of Operation), k and A
(87K and 87AP in the case of 87LP), with the applicable radius RAD
(87LPR or 87LPRS in the case of 87LP) and blocking angle BA (87LPA or
87LPAS in the case of the 87LP) settings.
Both conditions in Figure 3.19 (the overcurrent and Alpha Plane, if asserted)
receive further supervision from the master mode of the 87L function (87MTR
Relay Word bit). The relay inhibits this logic if the 87L function is blocked
locally or remotely (87BLK Relay Word bit asserted) or when it is in a local or
remote test mode (87TEST Relay Word bit asserted).
Upon satisfaction of all Figure 3.19 conditions, the 87LP logic drives the
output Relay Word bit 87L. The response is instantaneous if the disturbance
detector is picked up (87DD Relay Word bit asserted, see Disturbance
Detection Logic for more details). If the 87DD Relay Word bit is not asserted,
the element operates after a two-cycle intentional time delay for security (see
87L Theory of Operation for more discussion on the merits of disturbance
detection supervision).
The Figure 3.19 logic is identical for all three phases of the 87LP element.
The relay consolidates output Relay Word bits, 87LA, 87LB, and 87LC into a
single 87LP Relay Word bit for your convenience and routes these bits to the
trip logic (see Trip Logic for more details).
When the relay is in test mode, the raw output of the Alpha Plane operating
characteristic, with supervision only from the overcurrent check, is available
as the 87TOUT Relay Word bit (see Section 16: Relay Word Bits for more
information).
87USAFE is used to block the 87L function when the 87L data becomes
unreliable. This could be caused by the channel becoming unsynchronized or
the data becoming corrupted in the transmission path.
Table 3.3 87LP Phase Differential Elements Settings
Setting Description Range Default
87LPP Pickup threshold of the phase differential ele-
ment in the normal security mode (pu)
OFF, 0.1–2 1.2
87LPR Radius of the phase differential element in the
normal security mode
1.2–8 6
87LPA Blocking angle of the phase differential ele-
ment in the normal security mode (deg)
90–270 195
87LPPS
a
a
Advanced settings (EADVS = Y).
Pickup threshold of the phase differential ele-
ment in the extended security mode (pu)
OFF, 0.1–2 1.44
87LPRS
a
Radius of the phase differential element in the
extended security mode
1.2–8 7.2
87LPAS
a
Blocking angle of the phase differential ele-
ment in the extended security mode (deg)
90–270 234