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Date Code 20011026
Maintenance and Testing
7-41
SEL-321/321-1 Instruction Manual
Step 3.
Connect the voltage sources to the A-phase, B-phase, and C-phase to neutral relay
voltage inputs. Connect the current source to the A-phase relay current input. Refer
to the voltage and current connections shown in Figure 7.6 as an example.
Step 4.
Select the magnitude of the test signals, I
A
and V
A
.
Table 7.4 summarizes the test quantities for the Zone 2 A-G ground distance element
based upon the example relay settings.
Table 7.4: Test Quantities for Zone 2 Ground Mho Distance Element
Test Voltages
Test Current
V
A
= 40.4
∠
0° volts
I
TEST
= 2.5
∠
-82.42° amps
V
B
= 67.0
∠
-120° volts
V
C
= 67.0
∠
120° volts
The following text describes a hand calculation method you may use to calculate
relay distance element voltage and current test signals. If you do not wish to review
this information, go to Step 5.
You may want to use the Basic program ONEBUS to calculate distance element test
quantities. A listing of this program is provided in
Appendix D
.
The relay ground distance elements operate based upon the magnitude of applied
phase-ground impedance. The impedance calculation is supervised by the functions
described. To effectively test the distance elements, select test signals that fulfill the
impedance and supervisory requirements of the relay, but are within the ability of the
test sources to produce accurately.
The Zone 2 ground distance element is forward-reaching in the example relay
settings. Thus, it is supervised by the forward directional element 32QF, as well as
the 50L2 and 50G2 phase and residual overcurrent elements. Applied phase current
must exceed the 50L2 setting, applied residual current must exceed the 50G2 setting,
and applied 3I
2
must exceed the 50QF setting.
The 50L overcurrent elements operate based upon the magnitude of the phase
current. Using the current connections shown in Figure 7.6, the magnitude of I
A
is
equal to the magnitude of the applied test current. With a 50L2 setting of 0.90 amps,
50L2 picks up when I
TEST
is greater than 0.90 amps.
The 50G overcurrent elements operate based upon the magnitude of the residual
current. Using the current connections shown in Figure 7.6, the magnitude of I
R
is
equal to the magnitude of the applied test current, I
A
. With a 50G2 setting of 0.60
amps, 50G2 picks up when I
TEST
is greater than 0.60 amps.
The 50QF negative-sequence overcurrent element operates based upon the
magnitude of 3I
2
applied. Using the current connections shown in Figure 7.6, we can
calculate the magnitude of 3I
2
applied based upon the magnitude of I
TEST
.
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