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7-38
Maintenance and Testing
Date Code 20011026
SEL-321/321-1 Instruction Manual
Calculate the magnitude of I
TEST2
using Equation 7.11.
(
)
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
7.11
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-321 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 GMHOZ setting. You may
set the ground distance elements to reach in the forward or reverse direction. 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.
Each zone has an instantaneous indication. For example, the Z3G element asserts without
intentional time delay for A-G, B-G, and C-G faults within the Zone 3 mho or quadrilateral
characteristic. Zones 2, 3, and 4 also include time delayed indication through elements Z2GT,
Z3GT, and Z4GT. In addition, each individual phase-ground distance element provides an
instantaneous indication for each zone. For example, the MAG1, MAG2, MAG3, and MAG4
elements provide instantaneous indication of A-G ground faults in each zone.
For general testing, use the instantaneous and time delayed elements that respond to any phase-
ground fault within a given zone such as Z1G, Z2G, etc. You can record more detailed and
specific test results using the instantaneous element associated with the faulted phase and zone
under test.
There are a number of supervisory conditions that must be fulfilled before the relay allows a
ground distance element to pick up. These supervisory conditions are described below.
Summary of Contents for SEL-321
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