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7-34
Maintenance and Testing
Date Code 20011026
SEL-321/321-1 Instruction Manual
Step 3.
Connect the voltage sources to the relay A-phase, B-phase, and C-phase voltage
inputs. Connect the current source to the relay B-phase and C-phase current inputs.
Refer to the voltage and current connections shown in Figure 7.7 as an example.
Step 4.
Select the magnitude of the test signals, I
BC
, V
B
, and V
C
.
Table 7.3 summarizes the test quantities for the Zone 2 B-C phase distance element
based upon the example relay settings.
Table 7.3: Test Quantities for Zone 2 Phase Distance Element
Test Voltages
Test Current
V
A
= 67
∠
0° volts
I
TEST
= 2.5
∠
-173.97° amps
V
B
= 46.8
∠
-150° volts
V
C
= 46.8
∠
150° 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 phase distance elements operate based upon the magnitude of applied
phase-to-phase impedance. The impedance calculation is also supervised by the
functions described. To effectively test the distance elements, select voltage and
current test signals that fulfill the impedance and supervisory requirements of the
relay settings, but are within the ability of the voltage and current test sources to
produce accurately.
The Zone 2 phase distance element is forward-reaching in the example relay settings.
Thus, it is supervised by the forward directional element 32QF, as well as the 50PP2
phase-to-phase overcurrent elements. For the distance element to assert, the applied
phase-to-phase current must exceed the 50PP2 setting and applied 3I
2
must exceed
the 50QF setting.
The 50PP overcurrent elements operate based upon the magnitude of the vector
difference between any two phase currents. Using the current connections shown in
Figure 7.7, the magnitude of I
BC
is twice the magnitude of the applied current. This
is illustrated by the following equations.
TEST
BC
B
BC
C
B
BC
C
B
TEST
I
•
2
I
I
•
2
I
I
I
I
I
I
I
=
=
−
=
−
=
=
With a 50PP2 setting of 2.22 amps, 50PP2 picks up when I
TEST
is greater than 1.11
amps.
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