Sel 411L - Figure 3.46 Magnetizing Inrush and Overexcitation Blocking Logic

P.3.88
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
87L Differential Elements
Figure 3.46 Magnetizing Inrush and Overexcitation Blocking Logic
Detailed Description of Settings
E87HB
NOTE: With both E87HB and E87HR
set to N, the 87LP element will not
operate at all.
Choose among harmonic blocking, harmonic restraint, or both to obtain relay
security during transformer inrush conditions. Select E87HB = Y to enable
operation of the 87LP element in the harmonic blocking mode. Selecting
E87HB = N disables operation in the harmonic blocking mode by asserting
the blocking signal permanently. Note that with both E87HB and E87HR set
to N, the 87LP element will not operate at all.
Note that the relay always operates in cross-blocking (common harmonic
blocking) mode. Harmonic blocking refers to blocking the 87LP Alpha Plane
with the second, fourth, and fifth harmonics. The harmonic restrained 87LP
Alpha Plane uses a built in fifth harmonic blocking for overexcitation
conditions that is independent from the E87HB setting.
E87HR
Choose among harmonic blocking, harmonic restraint, or both to obtain relay
security during transformer inrush conditions. Select E87HR = Y to enable
operation of the 87LP element in the harmonic restrained mode. Selecting
E87HR = N disables operation in the harmonic restrained mode by asserting
the blocking signal permanently. Note that with both E87HB and E87HR set
to N, the 87LP element will not operate at all.
When in the harmonic restrained mode, the element uses the fifth
harmonic
blocking for overexcitation conditions without the need to enable harmonic
blocking.
87PCT2, 87PCT4, 87PCT5
These settings specify the minimum percentage harmonic levels expected
during magnetizing inrush conditions (87PCT2 and 87PCT4) or steady state
overexcitation conditions (87PCT5). Note that the same values of the 87PCT2
and 87PCT4 settings are used to control the amount of harmonic restraining
(see Figure 3.48) and harmonic blocking (see Figure 3.45) for the phase
differential element. The 87PCT5 setting controls the blocking level for both
the 87LP and 87LQ elements under steady state overexcitation conditions.
Φ = A, B, C
87ΦBK5
87XBK2
87ΦBK5
Relay Word Bit
Relay Word Bits
Setting
E87HB = N
Relay Word Bit
87HBΦ
Relay Word Bit
87HRΦ
Setting
E87HR = N
Stall the
dropout
timer
Stall the
dropout
timer
1.5 cyc
1 cyc
1.5 cyc
1 cyc
NOTE: For optimum performance,
always enable harmonic restraint,
i.e., set E87HR = Y.