Date Code 20011205
Testing and Troubleshooting
13-39
SEL-311A Instruction Manual
(
)
(
)
TEST
2
C
B
TEST
A
C
B
2
A
2
C
B
2
A
3
1
2
I
I
3
:
so
,
0
I
I
and
I
I
I
a
I
a
I
I
3
I
a
I
a
I
I
=
×
=
=
=
×
+
×
+
=
×
×
+
×
+
×
=
With a 50QF setting of 0.5 amps, 50QF picks up when I
TEST
is greater than 0.5 amps.
Select the magnitude of I
A
greater than the 50L2, 50GZ2, and 50QF settings, but less
than the maximum current output capability of the current test source.
In this example, select
│
I
TEST
│
= 2.5 amps. This selection fulfills the supervisory
overcurrent conditions described above.
The reach of the distance element under test in secondary ohms is defined by the
element setting. In this case Z2MG = 9.36
W
. The impedance measured by the relay
for a ground fault is determined by the faulted phase voltage, faulted phase current,
and the residual current multiplied by the zero-sequence current compensation
factor, k0. The SEL-311A Relay uses k0M1 and k0A1 settings to define the zero-
sequence current compensation factor for Zone 1 ground distance elements. When
the advanced user settings are not enabled (EADVS = N), the remaining zone
settings, k0M and k0A, follow k0M1 and k0A1. The impedance measured by the
relay ground mho distance element for a Zone 2 fault is defined by the following
equation:
R
A
A
AG
I
0
k
I
V
Z
×
+
=
Equation
13.11
Where: k0 = k0M
Ð
k0A°
For a fault on a radial system and when testing a ground distance element using a
single current source, I
A
= I
R
. In this case, Equation 13.11 can be simplified:
(
)
0
k
1
I
V
Z
A
A
AG
+
×
=
Equation
13.12
If we multiply both sides of Equation 13.12 by the quantity (1 + k0), the result is the
impedance applied by the A-phase test signals, V
A
and I
A
.
(
)
A
A
AG
I
V
0
k
1
Z
=
+
×
Equation
13.13
Since we are testing the Zone 2 mho ground distance element, the intended value of
Z
AG
= Z2MG = 9.36
W
. The angle of Z2MG is equal to the angle of positive-
sequence impedance, Z1ANG.
Because the element under test is not a Zone 1 element, the k0 value is defined by
the relay settings k0M and k0A. When you test the relay Zone 1 ground elements,
use k01M and k01A to define the magnitude and angle of k0.
Calculate the value of Z
AG
×
(1 + k0) based upon the information above.
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