Date Code 20011205
Testing and Troubleshooting
13-35
SEL-311A Instruction Manual
Slowly increase the magnitude of current applied until the M2P element asserts,
causing OUT106 to close. This should occur when current applied is approximately
2.5 amps.
With these signals applied, the relay measures B-C phase impedance defined by the
equation:
sec
,
ohms
I
2
V
Z
TEST
BC
BC
×
=
Equation
13.9
You may wish to test the distance element characteristic at impedance angles other
than the line positive-sequence impedance angle. To do this, you must adjust the
magnitude and angle of I
TEST
from the values shown in Table 13.3. As an example,
calculate the current signal necessary to test the distance element at an angle of
38.97°.
First, the new desired impedance angle (38.97°) is 45° less than the original test
impedance angle (83.97°). Add 45° to the angle of I
TEST1
.
°
-
=
Ð
°
+
°
-
=
Ð
°
+
Ð
=
Ð
97
.
128
I
45
97
.
173
I
45
I
I
2
TEST
2
TEST
1
TEST
2
TEST
Calculate the magnitude of I
TEST2
using Equation 13.10.
(
)
sec
,
amps
Angle
pedance
Im
Test
New
Angle
pedance
Im
Line
cos
I
I
1
TEST
2
TEST
-
=
(
)
( )
amps
54
.
3
I
amps
45
cos
5
.
2
I
amps
97
.
38
97
.
83
cos
5
.
2
I
2
TEST
2
TEST
2
TEST
=
°
=
°
-
°
=
Equation
13.10
Note:
As you perform this test, other protection elements may assert, causing the relay to
close other output contacts and assert relay targets. This is normal and is not a cause
for concern
Ground Mho Distance Elements
The SEL-311A Relay includes up to four zones of mho ground distance protection. Enable the
number of ground distance zones you would like to apply using the E21MG setting. Zones 1 and
2 are fixed forward. Zones 3 and 4 may be set forward or reverse. The reach and direction of
each zone is independent from the other zones. When a zone of phase distance protection is set
to reach in one direction, the ground distance elements associated with that zone must be set to
reach in the same direction. Reach is set in secondary ohms. The angle of maximum reach of
the ground distance elements is defined by the Z1ANG setting and the zero-sequence current
compensation factor for the zone under test.
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