Sel 411L - Figure 3.19 87 LP Phase Differential Element Logic; Table 3.4 87 LP Phase Differential Elements Analog Quantities

P.3.33
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
87L Differential Elements
Figure 3.19 87LP Phase Differential Element Logic
Figure 3.20 presents the overcurrent comparator in detail. The comparator
compares a full-cycle cosine-filtered magnitude of the differential current, ID,
with a pickup threshold, PKP. The logic inhibits the output if the PKP pickup
setting is set to OFF. The same internal logic of the overcurrent comparator,
with adequate operating quantities and settings, applies to the phase, negative-
sequence, and zero-sequence differential elements.
Figure 3.21 presents the Alpha Plane comparator in detail. In general, the
permissive output asserts for the following.
The Alpha Plane ratio, k, is not greater than the reciprocal of the outer
radius, RAD, or the Alpha Plane angle, A, is not in the blocking region
the BA blocking angle specifies.
Note that the logic calculates the ratio in the generalized Alpha Plane as the
ratio of the smaller to higher equivalent currents, so the ratio is always a
number less than or equal to 1. All relays will calculate and display the same
value of the ratio and the angle (see 87L Theory of Operation), simplifying the
Alpha Plane comparator logic of Figure 3.21.
Table 3.4 87LP Phase Differential Elements Analog Quantities
Name Description Units
87IAFM Differential current magnitude, A-phase, full-cycle
cosine-filtered
pu
87IBFM Differential current magnitude, B-phase, full-cycle
cosine-filtered
pu
87ICFM Differential current magnitude, C-phase, full-cycle
cosine-filtered
pu
87KA Ratio of equivalent Alpha Plane, A-phase –
87KB Ratio of equivalent Alpha Plane, B-phase –
87KC Ratio of equivalent Alpha Plane, C-phase –
87APAA Angle of equivalent Alpha Plane, A-phase Deg (180°)
87APAB Angle of equivalent Alpha Plane, B-phase Deg (180°)
87APAC Angle of equivalent Alpha Plane, C-phase Deg (180°)
Analog
87I
ΦFM
Analogs
87K
Φ
87APAΦ
Relay Word Bit
87L50
Φ
Relay Word Bit
87L
Φ
(to trip logic)
2 cyc
0
Relay Word Bit
87DD
Relay Word Bit
87LA
87LB
87LC
Relay Word Bit
87LP
Relay Word Bit
87MTR
87BLK
87USAFE
87TEST
Test Point
(to test mode logic)
Settings
87LPP
87LPPS
Relay Word Bit
87LPSEC
87LPR
87LPRS
87LPA
87LPAS
RAD
BA
AP
Alpha Plane
Comparator
k
A
ID
PKP
OC
Overcurrent
Comparator
Φ = A, B, C
0
1
0
1
0
1
0 cyc
2 cyc