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7-42
Maintenance and Testing
Date Code 20011026
SEL-321/321-1 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, 50G2, 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
Ω
. 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-321 Relay uses k01M and k01A settings to define the zero-
sequence current compensation factor for Zone 1 ground distance elements. The
k0M and k0A settings to define k0 for the remaining zones. 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
7.12
Where: k0 = k0M
∠
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 7.12 can be simplified:
(
)
0
k
1
I
V
Z
A
A
AG
+
⋅
=
Equation
7.13
If we multiply both sides of Equation 7.13 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
7.14
Since we are testing the Zone 2 mho ground distance element, the intended value of
Z
AG
= Z2MG = 9.36
Ω
. 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.
Содержание SEL-321
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Страница 78: ...2 54 Specifications Date Code 20011026 SEL 321 321 1 Instruction Manual Figure 2 4 Logic Symbol Legend ...
Страница 87: ...Date Code 20011026 Specifications 2 63 SEL 321 321 1 Instruction Manual Figure 2 21 Load Encroachment Logic ...
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