Sel 411L - Table 3.34 87 L Relay Word Bits Related to Harmonic Blocking and Restraining

P.3.89
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
87L Differential Elements
Older types of transformers produce considerable harmonic levels during
inrush conditions allowing higher values of the 87PCT2 and 87PCT4 settings
maintaining better dependability margins for internal faults with possible CT
saturation. Newer transformers constructed using core material with better
magnetic properties may generate lower levels of harmonics during inrush
conditions, calling for the 87PCT2 and 87PCT4 settings to be lowered. Note
that the cross-phase blocking logic allows you to keep the settings relatively
high in such cases, as typically only one phase will experience lower harmonic
content during inrush.
Make sure the CTs are rated in such a way that they do not saturate for several
power cycles for a heavy internal fault (such as a fault at the transformer
terminals) giving the element a chance to operate before the harmonic
blocking or restraining impair dependability because of spurious harmonics
caused by CT saturation. This is particularly relevant if the 87PCT2, 87PCT4
and 87PCT5 settings are set very low, such as below 10 percent.
Note that in the harmonic restrained mode of operation, the Alpha Plane
settings determine the amount of extra restraint you need to ensure security
during inrush conditions. The more secure the Alpha Plane settings (higher
radius and blocking angle) the less extra restraint you need from the
harmonics. Therefore, with higher Alpha Plane settings, you can also use
higher 87PCT2 and 87PCT4 settings.
87LP Phase Differential Element With In-Line Transformers
In reference to Figure 3.47, the phase differential element, 87LP, incorporates
a high-set (unrestrained) operating path, as well as a harmonic restrained
Alpha Plane path (in addition to the traditional harmonic blocked Alpha Plane
operating path) in applications with in-line transformers.
Table 3.34 87L Relay Word Bits Related to Harmonic Blocking and Restraining
Name Description
87ABK2 Second harmonic present in A-phase differential current
87BBK2 Second harmonic present in B-phase differential current
87CBK2 Second harmonic present in C-phase differential current
87XBK2 Cross-phase second harmonic (second harmonic in any phase)
87QB Harmonic blocking asserted for the 87LQ element (second or fifth harmonic
block in any phase)
87ABK5 Fifth harmonic present in A-phase differential current
87BBK5 Fifth harmonic present in B-phase differential current
87CBK5 Fifth harmonic present in C-phase differential current
87HBA Harmonic blocking asserted in A-phase (permanently asserted if operation
with harmonic blocking is disabled)
87HBB Harmonic blocking asserted in B-phase (permanently asserted if operation
with harmonic blocking is disabled)
87HBC Harmonic blocking asserted in C-phase (permanently asserted if operation
with harmonic blocking is disabled)
87HRA Fifth harmonic blocking asserted in A-phase (permanently asserted if opera-
tion with harmonic restraining is disabled)
87HRB Fifth harmonic blocking asserted in B-phase (permanently asserted if opera-
tion with harmonic restraining is disabled)
87HRC Fifth harmonic blocking asserted in C-phase (permanently asserted if opera-
tion with harmonic restraining is disabled)