I.L. 40-385.7
5-4
a.
Setting the Inner Blinder (21BI)
If the OSB is used to supervise tripping of the 3
φ
unit on heavy load current, the inner blind-
er 21BI must be set sufficiently far apart to accommodate the maximum fault arc resistance.
A reasonable approximation of arc resistance at fault inception is 400 volts per foot. If a
maximum ratio of “line voltage per spacing” is 10,000 volts/ft. for a high voltage transmis-
sion line, and if a minimum internal 3-phase fault current is calculated as:
I
min.
=
[E / 1.73(Z
A
+Z
L
)]
where Z
A
is maximum equivalent source impedance, Z
L
is line impedance and E is line-to-line
voltage.
then R
max
.
= 400 x FT / I
min.
=
400x1.73(Z
A
+Z
L
)/10000
=
0.0693 (Z
A
+Z
L
)
Adding a 50% margin to cover the inaccuracies of this expression:
R
max.
=
0.104(Z
A
+Z
L
) primary ohms
R
S
=
0.104(Z
A
+Z
L
)R
C
/R
V
secondary ohms
Set inner blinder to:
R
T
= R
S
x COS (90
°
- PANG)
(1)
This is the minimum permissible inner blinder setting when it is used to provide a restricted trip
area for a distance relay.
Another criterion that may be considered is based upon the rule of thumb that stable swings
will not involve an angular separation between generator voltages in excess of 120
°
. This would
give an approximate maximum of:
Z
inner
=
(Z
A
+Z
L
+Z
B
)/ (2x1.73)
(2)
=
0.288(Z
A
+Z
L
+Z
B
) primary ohms
Z
inner
=
0.288(Z
A
+Z
L
+Z
B
)R
C
/R
V
secondary ohm
where Z
B
is the equivalent maximum source impedance at the end of the line away from Z
A
.
An inner blinder setting between the extremes of equations (1) and (2) may be used. This pro-
vides operation for any 3-phase fault with arc resistance, and restraint for any stable swing. Ex-
cept in those cases where very fast out-of-step swings are expected, the larger setting can be
used.
It will usually be possible to use the minimum inner blinder setting of 1.5 ohms.
Summary of Contents for REL-300
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Page 29: ...I L 40 385 7 1 12 Figure 1 4 Simplified Block Diagram of REL300 Relay Sub 6 9651A07 ...
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Page 43: ...I L 40 385 7 2 13 Figure 2 8 REL300 Outline Drawing Sub 2 2403F38 ...
Page 44: ...I L 40 385 7 2 14 Figure 2 9 REL300 Backplane Rear View Sub 11 2420F01 ...
Page 71: ...I L 40 385 7 3 27 Figure 3 1 REL300 Characteristics R X Diagram 9651A57 Sub 3 ...
Page 74: ...I L 40 385 7 3 30 Figure 3 5 REL300 Zone 1 Trip Logic 9661A16 Sub 1 ...
Page 75: ...I L 40 385 7 3 31 Figure 3 6 REL300 Zone 2 Trip Logic 9658A84 Sub 2 ...
Page 76: ...I L 40 385 7 3 32 Figure 3 7 REL300 Zone 3 Trip Logic 1504B04 Sub 1 ...
Page 78: ...I L 40 385 7 3 34 Figure 3 10 Loss of Potential Logic 9662A61 Sub 1 ...
Page 83: ...I L 40 385 7 3 39 Figure 3 17 Load Loss Accelerated Trip Logic 9656A33 Sub 2 ...
Page 85: ...I L 40 385 7 3 41 Figure 3 19 Reclosing Initiation Logic 1504B45 Sub 1 ...
Page 88: ...I L 40 385 7 3 44 Figure 3 24 PUTT Keying Logic Sub 2 9657A62 ...
Page 89: ...I L 40 385 7 3 45 Figure 3 25 Blocking System Logic 1504B89 Sub 1 ...
Page 94: ...I L 40 385 7 3 50 Figure 3 33 Composite Signal For Programmable Output Contacts Sub 2 1504B08 ...
Page 110: ...I L 40 385 7 4 13 Figure 4 1 REL300 Backplate Sub 8 1354D22 Sheet 4 of 5 ...
Page 111: ...I L 40 385 7 4 14 Figure 4 2 REL300 Backplane PC Board Terminals Sub 1 1611C78 ...
Page 112: ...I L 40 385 7 4 15 Figure 4 3 REL300 Systems External Connection Sub 3 1502B21 ...
Page 169: ...I L 40 385 7 B 7 Figure B 2 Test Connection for Three Phase Faults 1502B51 Sub 1 Sheet 2 of 4 ...
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