7. TESTING
ADDITIONAL FUNCTIONAL TESTING
7-11
7.3.3
UNBALANCE TEST
The SR469 measures the ratio of negative sequence current (I
2
) to positive sequence current (I
1
). This value as a percent is used as the
unbalance level when motor load exceeds FLA. When the average phase current is below FLA, the unbalance value is derated to prevent
nuisance tripping as positive sequence current is much smaller and negative sequence current remains relatively constant. A sample
calculation is given below.
The derating formula is:
I
I
Iavg
FLA
x
2
1
100%
×
Figure 7-2 THREE PHASE EXAMPLE FOR UNBALANCE CALCULATION
Symmetrical component analysis of vectors using the mathematic vector convention yields a ratio of negative sequence
current to positive sequence current as shown:
I
I
Ia a Ib aIc
Ia aIb a Ic
j
2
2
2
1
1
3
1
3
1 120
0 5
0 866
=
+
+
+
+
∠
° = −
+
(
)
(
)
.
.
where a =
I
I
2
2
2
1
780 0
1 120
1000
113
1 120
1000 113
780 0
1 120
1000
113
1 120
1000 113
=
∠ °+ ∠
°
∠ −
° + ∠
°
∠
°
∠ °+ ∠
°
∠ −
° + ∠
°
∠
°
(
) (
) (
)(
)
(
)(
) (
) (
)
I
I
2
1
780 0
1000 127
1000 233
780 0
1000 7
1000 353
=
∠ °+
∠
°+
∠
°
∠ °+
∠ °+
∠
°
)
I
I
j
j
j
j
2
1
780
6018
798 6
6018
798 6
780
992 5
1219
992 5
1219
=
−
+
+ −
−
+
+
+
−
.
.
.
.
.
.
.
.
I
I
2
1
423 6
2765
=
−
.
I
I
2
1
=
-0.1532
if, FLA=1000
Iavg
A
A
A
A
=
+
+
=
780
1000
1000
3
926 7
.
and since, (Iavg =926.7A) < (FLA=1000)
SR
x
469
0 1532
926 7
1000
100%
14 2%
UNBALANCE
= −
×
=
.
.
.
Summary of Contents for SR469
Page 7: ......
Page 19: ...2 INSTALLATION MECHANICAL 2 5 2 1 5 TERMINAL LOCATIONS Figure 2 11 TERMINAL LAYOUT...
Page 21: ...2 INSTALLATION ELECTRICAL 2 7 Figure 2 12 TYPICAL WIRING DIAGRAM...
Page 32: ...ELECTRICAL 2 INSTALLATION 2 18 2 2 14 TYPICAL 2 SPEED MOTOR WIRING...
Page 39: ...OVERVIEW 3 SR469 OPERATION 3 6 yy SETPOINTS yy S1 SR469 SETUP...
Page 104: ...4 SETPOINT PROGRAMMING S11 MONITORING 4 65 Figure 4 24 TRIP COIL SUPERVISION...
Page 113: ...S12 ANALOG I O 4 SETPOINT PROGRAMMING 4 74...
Page 244: ...8 469PC PROGRAM WAVEFORM CAPTURE 8 13 Figure 8 11 WAVEFORM CAPTURE...
