Schweitzer Engineering Laboratories SEL-321 - Page 307

Date Code 20011026 Maintenance and Testing 7-37
SEL-321/321-1 Instruction Manual
()
volts03.22V
volts1508.4612011508.46240100.67V
2
3
1
2
°∠=
°∠⋅°∠+°−∠⋅°∠+°∠⋅=
Due to the test connections used, I
B
= -I
C
= I
TEST
.
°∠=
°−∠=
°∠=
03.6A5.2I
97.173A5.2I
0A0.0I
C
B
A
()
amps03.9644.1I
amps03.65.2120197.1735.2240100.0I
2
3
1
2
°∠=
°∠⋅°∠+°−∠⋅°∠+°∠⋅=
Using Equation 7.2 to calculate Z2c, the result is:
ohms47.15c2Z −=
() ( )
ohms91.2FT2Z
47.1525.077.025.1FT2Z
ohms47.15m2Z
−=
⋅−⋅=
=
The Z2FT threshold is -2.91 Ω. Z2c applied (-15.47 Ω) is less than the Z2FT
threshold based upon the Z2F setting (0.77 Ω) and Z2m (15.47 Ω), therefore, the
32QF element asserts when these signals are applied. If Z2c applied is greater than
the Z2FT threshold, select new test current and voltages using the steps outlined
above.
Step 5. Turn on the voltage sources. Apply V
A
, V
B
, and V
C
at the magnitudes and angles
listed in Table 7.3. Turn on the current test source. Set the current angle to -174°.
Slowly increase the magnitude of current applied until the M2P element asserts,
causing OUT7 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
I2
V
Z
TEST
BC
BC
⋅
=
Equation 7.10
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 7.3. 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
.
°−=∠
°+°−=∠
°+∠=∠
97.128I
4597.173I
45II
2TEST
2TEST
1TEST2TEST