13-32
Testing and Troubleshooting
Date Code 20011205
SEL-311A Instruction Manual
current test signals that fulfill the impedance and supervisory requirements of the
relay settings, but are within the ability of the voltage and current test sources to
produce accurately.
The Zone 2 phase distance element is forward-reaching. Thus, it is supervised by the
forward directional element 32QF, as well as the 50PP2 phase-to-phase overcurrent
elements. For the distance element to assert, the applied phase-to-phase current must
exceed the 50PP2 setting and applied 3I
2
must exceed the 50QF setting.
The 50PP overcurrent elements operate based upon the magnitude of the vector
difference between any two phase currents. Using the current connections shown in
Figure 13.6, the magnitude of I
BC
is twice the magnitude of the applied current. This
is illustrated by the following equations.
TEST
BC
B
BC
C
B
BC
C
B
TEST
I
•
2
I
I
•
2
I
I
I
I
I
I
I
=
=
-
=
-
=
=
With a 50PP2 setting of 2.22 amps, 50PP2 picks up when I
TEST
is greater than 1.11
amps.
The 50QF negative-sequence overcurrent element operates based upon the
magnitude of 3I
2
applied. Using the current connections shown in Figure 13.6, we
can calculate the magnitude of 3I
2
applied based upon the magnitude of I
TEST
.
(
)
(
)
(
)
(
)
(
)
°
-
Ð
=
-
=
-
=
-
=
=
+
+
=
+
+
=
90
732
.
1
•
I
I
•
3
a
a
•
I
I
•
3
I
•
a
I
•
a
I
•
3
:
so
,
I
I
and
0
I
I
•
a
I
•
a
I
I
•
3
I
•
a
I
•
a
I
•
I
B
2
2
B
2
B
B
2
2
B
C
A
C
B
2
A
2
C
B
2
A
3
1
2
Because the 50QF element operates based upon magnitude only, the equation above
is simplified.
732
.
1
•
I
I
•
3
TEST
2
=
With a 50QF setting of 0.5 amps, 50QF picks up when I
TEST
is greater than 0.288
amps.
In this example, select
│
I
TEST
│
= 2.5 amps, thus I
BC
= 5.0 amps and 3I
2
= 4.33 amps.
This selection fulfills the supervisory overcurrent conditions described above.
The reach of the distance element under test is defined by the element setting. In this
case Z2P = 9.36 secondary ohms.
Calculate the magnitude of V
BC
using Equation 13.7.
Содержание SEL-311A
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