Sel 411L - Figure 3.45 Harmonic Sensing Logic

P.3.87
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
87L Differential Elements
Figure 3.45 Harmonic Sensing Logic
These Relay Word bits are designed to deal with temporary dropout
conditions and to reflect the application intent of harmonic blocking or
restraining as shown in Figure 3.46.
The 87HB Relay Word bit is a blocking signal for the harmonic blocking
mode of operation of the 87LP element. The block is permanently asserted if
operation in the harmonic blocking mode is not enabled (E87HB = N). When
operation in the harmonic blocking mode is enabled (E87HB = Y), the block
asserts if the fifth harmonic overexcitation condition is sensed via the 87BK5
Relay Word bit, or magnetizing inrush is sensed using the second and fourth
harmonics in any phase (cross-blocking) as signaled by the 87XBK2 Relay
Word bit.
When 87HB asserts, the logic instantaneously blocks the differential
elements. If 87HB asserts for 1.5 power system cycles, a drop off timer
extends the blocking signal for 1 power system cycle. Should the block
reassert while the dropout timer is timing out, the dropout timer is stalled for
extra security until the blocking Relay Word bits in Figure 3.45 deassert again.
The 87HR Relay Word bit is a blocking signal for the harmonic restraining
mode of operation of the 87LP element. The block is permanently asserted if
operation in the harmonic restraining mode is not enabled (E87HR = N).
When operation in the harmonic restraining mode is enabled (E87HR = Y),
the block asserts when 87BK5 Relay Word bit asserts. No other harmonics
block the harmonic restrained 87LP element. For magnetizing inrush
conditions, the second and fourth harmonics secure the harmonic restrained
87LP element.
When 87HR asserts, the logic instantaneously blocks the differential
elements. If 87HR asserts for 1.5 power system cycles, a drop off timer
extends the blocking signal for 1 power system cycle. Should the block re-
assert while the dropout timer is timing out, the dropout timer is stalled for
extra security until the blocking 87BKT Relay Word bit in Figure 3.45
deasserts again.
-
+
-
+
-
+
-
+
Φ = A, B, C
87IΦ2M
87IΦFM
87IΦ4M
87IΦ5M
87HBOC
100
87PCT2
100
87PCT4
100
87PCT5
87ΦBK2
Relay Word Bit
87QB
Relay Word Bits
87XBK2
87ΦBK5
2 other
phases
2 other
phases
Calibration Settings
87HBOC 0.05 pu (87L)