Sel 411L - Table 3.32 87 L Applications with In-Line Transformers Harmonic Blocking and Restraining Settings; Table 3.33 Analog Quantities Related to Harmonic Blocking and Restraining

P.3.86
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
87L Differential Elements
 = A, B, C.
Figure 3.45 presents the harmonic sensing logic.
This logic compares the levels of the second, fourth and fifth harmonics in the
differential current (87I2M, 87I4M and 87I5M, respectively) with the
level of the fundamental frequency component in the differential current
(87IFM, where  = A, B or C), using the percentage blocking settings
87PCT2, 87PCT4 and 87PCT5, respectively. The comparison is allowed once
the fundamental frequency component in the differential current is above the
noise level specified by the factory constant of 0.05 pu (87HBOC calibration
setting).
If the second or fifth harmonic content in the differential current exceeds the
respective settings, Relay Word bit 87QB asserts. The logic uses this Relay
Word bit to block the negative-sequence differential element, 87LQ.
Similarly, the second or fourth harmonic content asserts Relay Word bit
87BK2 to block the phase differential element, 87LP. Furthermore, if Relay
Word bit 87BK2 asserts in any phase, Relay Word bit 87XBK2 asserts. We
use Relay Word bit 87XBK2 for cross-phase blocking.
The fifth harmonic level is sensed via the 87BK5 Relay Word bit intended
for blocking both the 87LP and 87LQ under steady state overexcitation of the
transformer core.
Table 3.32 87L Applications With In-Line Transformers Harmonic Blocking
and Restraining Settings
Setting Description Range Default
E87HR Enable 87LP element with harmonic restraint Y, N N
E87HB Enable 87LP element with harmonic blocking Y, N Y
87PCT2 Second harmonic percentage value for harmonic
blocking or restraint (%)
OFF, 5–100 15
87PCT4 Fourth harmonic percentage value for harmonic
blocking or restraint (%)
OFF, 5–100 15
87PCT5 Fifth harmonic percentage value for harmonic
blocking (%)
OFF, 5–100 35
Table 3.33 Analog Quantities Related to Harmonic Blocking and Restraining
Name Description Units
87IFM Magnitude of the fundamental frequency component in the differ-
ential current, full-cycle cosine filtered, phase 
pu
87I2M Magnitude of the second harmonic in the differential current,
full-cycle cosine filtered, phase 
pu
87I4M Magnitude of the fourth harmonic in the differential current, full-
cycle cosine filtered, phase 
pu
87I5M Magnitude of the fifth harmonic in the differential current, full-
cycle cosine filtered, phase 
pu
NOTE: For optimum performance,
always enable harmonic restraint, i.e.,
set E87HR = Y.