ABB REL 301, Инструкция

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I.L. 40-386.4
3-6
• Inner blinder should not operate on severe stable swings
• Outer blinder must have adequate separation from inner blinder for fastest out-of-step swing
to be acknowledged as an out-of-step condition
• Outer blinder must not operate on load
a. Setting the Inner Blinder
If the out of step blocking (OSB) is used to supervise tripping of the 3Ø unit on heavy load
current, the inner blinder 21BI must be set sufficiently far apart to accommodate the maxi-
mum 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 transmission 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.
= 400 x 1.73(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:
“OS Inner” = R
T
= R
S
x COS (90
o
- 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
o
. This
would give an approximate maximum of:
“OS Inner” = (Z
A
+Z
L
+Z
B
)/ (2x1.73) (2)
= 0.288(Z
A
+Z
L
+Z
B
) primary ohms
“OS Inner” = 0.288(Z
A
+Z
L
+Z
B
)R
C
/R
V
secondary ohms
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
provides operation for any 3-phase fault with arc resistance, and restraint for any stable
swing. Except 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.
b. Setting the Outer Blinder