Schweitzer Engineering Laboratories SEL-751 - Table 4.30 Second-Harmonic Blocking Settings; Figure 4.58 Three-Phase Second- and Fifth-Harmonic Blocking Logic

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Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
Figure 4.58 Three-Phase Second- and Fifth-Harmonic Blocking Logic
Second- and fifth-harmonic blocking elements are typically used to supervise
sensitive overcurrent elements. CT saturation during faults can cause the relay
to measure harmonic currents. The harmonic blocking elements may also
assert briefly when the fundamental frequency current changes. Either condi-
tion might delay the supervised element. Set an unsupervised element above
the expected inrush current to provide fast protection during large faults. Set
the harmonic blocking timer pickup for more than one cycle in applications
that cannot tolerate the element operating because of current changes.
EXAMPLE 4.13 Instantaneous Overcurrent Element Blocking
In this example, including second-harmonic blocking element HBL2T in the
torque-control equation for Level 1 phase overcurrent element 67P1 helps
prevent operation because of transformer inrush.
50P1P := 10.00 A
50P2P := 20.00 A
50P1D := 0.03 sec
50P1TC := !HBL2T
50P2TC := 1
TR := …+ 67P1T + 67P2T +…
The Level 1 time delay 50P1D allows time for the blocking element to assert.
Level 2 phase overcurrent element setting 50P2P is high enough that the
element does not operate when the line is energized but low enough to
operate for high current faults when current transformer saturation or
fundamental frequency current change might briefly block the Level 1
element.
EXAMPLE 4.14 Time-Overcurrent Element Blocking
For time-overcurrent elements, it may be desirable for the element to
continue timing when transformer inrush is detected, yet trip the breaker if
the time-overcurrent element remains asserted after the inrush conditions
have subsided.
Table 4.30 Second-Harmonic Blocking Settings
Setting Prompt Setting Range
Setting Name :=
Fac to ry Default
2ND HARM BLOCK Y, N EHBL2 := N
2ND HARM PU 5–100% HBL2P := 10
2ND HARM PU DLY 0.00–320.00 sec HBL2PU := 0.00
2ND HARM DO DLY 0.00–320.00 sec HBL2DO := 0.00
2ND HARM TC SEL
OGIC HBL2TC := 1
5TH HARM BLOCK Y, N EHBL5 := N
5TH HARM PU 5–100% HBL5P := 10
5TH HARM PU DLY 0.00–320.00 sec HBL5PU := 0.00
5TH HARM DO DLY 0.00–320.00 sec HBL5DO := 0.00
5TH HARM TC SEL
OGIC HBL5TC := 1
Relay
Word
Bit
Relay
Word
Bits
HBL2BT
HBL2CT
HBL2AT
HBL2T