Sel 411L - Figure 3.48 87 LP Alpha Plane Concept with Harmonic Restraint; Table 3.36 87 LP Phase Differential Analog Quantities Specific to Applications with In-Line Transformers; Table 3.37 87 L Relay Word Bits Related Unrestrained 87 LP Operation

P.3.92
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
87L Differential Elements
Figure 3.48 87LP Alpha Plane Concept With Harmonic Restraint
Refer to 87L Elements for more information regarding supervising the 87LP
logic with the master mode (87MTR), test mode (87TEST), disturbance
detection (87DD) and the blocking action (87BLK). 87L Elements also
explains the application of normal and expanded security Alpha Plane settings
and their control via the 87LPSEC Relay Word bit.
Detailed Description of Settings
87LPU
The purpose of the instantaneous unrestrained current element is to react
quickly to heavy internal faults, signified by high current levels. The
unrestrained differential element responds to the fundamental frequency
component of the differential operating current (full-cycle cosine-filtered). It
is unaffected by the Alpha Plane radius and blocking angle settings or
harmonic restraint or blocking settings. Therefore, you must set the element
pickup level high enough that the element does not react to large inrush
currents. Typical values of this setting are in the range of several times the tap
value (6–8 pu are typical).
Table 3.36 87LP Phase Differential Analog Quantities Specific To
Applications With In-Line Transformers
Name Description Units
87KHRA Alpha Plane ratio, harmonic restrained, A-phase -
87KHRB Alpha Plane ratio, harmonic restrained, B-phase -
87KHRC Alpha Plane ratio, harmonic restrained, C-phase -
87HRAA Alpha Plane angle, harmonic restrained, A-phase Deg (±180°)
87HRAB Alpha Plane angle, harmonic restrained, B-phase Deg (±180°)
87HRAC Alpha Plane angle, harmonic restrained, C-phase Deg (±180°)
Fundamental frequency restraint
with harmonic boost from the EFD logic,
and charging current compensation
high-frequency components, phase
Φ
Harmonic-restrained
restraining signal,
phase
Φ
Generalized
Alpha Plane
87LP
(Harmonic
Restraint)
100
87PCT2
87IΦ2M
87IΦ4M
100
87PCT4
87KHRΦ
87HRAΦ
Differential phasor,
phase
Φ
Ratio and angle
of the harmonic-
restrained
Alpha Plane
Σ
Φ = A, B, C
Σ
Table 3.37 87L Relay Word Bits Related Unrestrained 87LP Operation
Name Description
87LUA Phase 87L element operated in the unrestrained mode (high-set) in A-phase
87LUB Phase 87L element operated in the unrestrained mode (high-set) in B-phase
87LUC Phase 87L element operated in the unrestrained mode (high-set) in C-phase
87LU Phase 87L element operated in the unrestrained mode (high-set)