Schweitzer Engineering Laboratories SEL-311C - Page 490

13.36
SEL-311C Relay Instruction Manual Date Code 20060320
Testing and Troubleshooting
Test Procedures
Equation 13.34
so:
Equation 13.35
Because the 50QF element operates based upon magnitude
only, the equation above is simplified.
Equation 13.36
With a 50QF setting of 0.5 amps, 50QF picks up when I
TEST
is
greater than 0.288 amps.
Step 11. In this example, select |I
TEST
| = 2.5 amps, thus I
BC
= 5.0 amps
and 3I
2
= 4.33 amps. This selection fulfills the supervisory
overcurrent conditions described above.
The reach of the distance element under test is defined by the
element setting. In this case, Z2P = 9.36 secondary ohms.
Step 12. Calculate the magnitude of V
BC
through use of
Equation 13.37.
Equation 13.37
Refer to Figure 13.8 and use the equations below to calculate
the magnitude and angle of V
B
and V
C
based upon the
magnitude of V
BC
calculated above.
I
2
1
3
---
I
A
a
2
I
B
aI
C
• +• +()• =
3I•
2
I
A
a
2
I
B
aI
C
• +• +()=
I
A
0 and I
C
I
B
–==
3I
2
• a
2
I
B
aI
B
• –•
()
=
I
B
=a
2
a–()•
I
B
= 1.732 90°–∠()•
3I
2
• I
TEST
1.732• =
V
BC
I
BC
Z
BC
• =
5.0 9.36• =
46.8 volts secondary=