Schweitzer Engineering Laboratories SEL-321 - Page 295

Date Code 20011026 Maintenance and Testing 7-25
SEL-321/321-1 Instruction Manual
Step 4. As described above, the relay 32Q element operates based upon the magnitude and
angle of negative-sequence voltages and currents. You can calculate the magnitude
and angle of V
2
and I
2
, given the magnitude and angle of each of the phase quantities
using the equations below.
()
()
CB
2
A
3
1
2
cB
2
A
3
1
2
I•aI•aI•I
V•aV•aV•V
++=
++=
Using single-phase signals simplifies the V
2
and I
2
calculations.
()
()
A
3
1
2
A
3
1
2
CB
CB
I•I
V•V
amps0II
volts0VV
=
=
==
==
Assume that you apply a test voltage V
A
= 18.0 ∠180° volts secondary.
()
volts1800.6V
volts1800.18•V
2
3
1
2
°∠=
°∠=
Determine the test angle of A-phase current from the Z1ANG relay setting. Equation
7.2 yields a positive result when I
2
lags V
2
by the angle of Z1ANG°. Equation 7.2
yields a negative result when I
2
leads V
2
by (180° - ∠Z1ANG°).
We are testing for positive values of Z2c, so I
2
should lag V
2
by Z1ANG.
Assuming that V
A
= 18.0 ∠180° volts, the angle of I
A
for this test should be 96°.
Determine the magnitude of A-phase current where Z2 equals Z2R or Z2F using
Equation 7.7:
()
22A
Z/V•3I = Equation 7.7
For Z2R = 5.45 Ω:
()
amps3.3I
ohms45.5volts0.6•3I
A
A
=
=
Calculate Z2m:
ohms45.5m2Z
A1.1
V0.6
m2Z
I
V
m2Z
2
2
=
=
=
Because Z2R is positive, use Equation 7.5 to calculate Z2RT.
() ()
ohms45.5RT2Z
45.5•25.045.5•75.0RT2Z
m2Z•25.0R2Z•75.0RT2Z
=
+=
+=