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.
(
)
(
)
C
B
2
A
3
1
2
c
B
2
A
3
1
2
I
•
a
I
•
a
I
•
I
V
•
a
V
•
a
V
•
V
+
+
=
+
+
=
Using single-phase signals simplifies the V
2
and I
2
calculations.
( )
( )
A
3
1
2
A
3
1
2
C
B
C
B
I
•
I
V
•
V
amps
0
I
I
volts
0
V
V
=
=
=
=
=
=
Assume that you apply a test voltage V
A
= 18.0
∠
180
°
volts secondary.
(
)
volts
180
0
.
6
V
volts
180
0
.
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:
(
)
2
2
A
Z
/
V
•
3
I
=
Equation
7.7
For Z2R = 5.45
Ω
:
(
)
amps
3
.
3
I
ohms
45
.
5
volts
0
.
6
•
3
I
A
A
=
=
Calculate Z2m:
ohms
45
.
5
m
2
Z
A
1
.
1
V
0
.
6
m
2
Z
I
V
m
2
Z
2
2
=
=
=
Because Z2R is positive, use Equation 7.5 to calculate Z2RT.
(
)
(
)
ohms
45
.
5
RT
2
Z
45
.
5
•
25
.
0
45
.
5
•
75
.
0
RT
2
Z
m
2
Z
•
25
.
0
R
2
Z
•
75
.
0
RT
2
Z
=
+
=
+
=
Содержание SEL-321
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