Negative Sequence Current Accuracy - GE 489 Instruction Manual
Generator management relay
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- Instruction manual (314 pages) ,
- Communications manual (78 pages) ,
- Instruction manual (38 pages)
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7 TESTING
The 489 measures negative sequence current as a percent of Full Load Amperes (FLA). A sample calculation of negative
sequence current is shown below. Given the following generator parameters:
Rated MVA ( P
) = 1.04
A
Voltage Phase to Phase ( V
P
A
we have:
FLA
=
---------------------- -
×
3 V
pp
With the following output currents:
∠
I
I
=
780 0°,
=
1000 113° lag,
a
b
The negative-sequence current Ins is calculated as:
1
2
(
)
I
-- - I
a
I
aI
=
+
+
ns
a
b
c
3
1
(
∠
(
∠
-- - 780 0°
1 120°
=
+
3
1
(
∠
∠
-- - 780 0°
1000 127°
=
+
3
141.2
=
–
I
⇒
ns
×
% I
=
---------- -
100
=
ns
FLA
Therefore, the negative sequence current is 14% of FLA. The specification for negative sequence current accuracy is per
output current inputs. Perform the steps below to verify accuracy.
1.
Alter the following setpoints:
S2 SYSTEM SETUP\GENERATOR PARAMETER\GENERATOR RATED MVA:
S2 SYSTEM SETUP\GENERATOR PARAMETER\VOLTAGE PHASE-PHASE:
(Note: This is equivalent to setting FLA = 1000 A – For testing purposes ONLY!)
S2 SYSTEM SETUP\CURRENT SENSING\PHASE CT PRIMARY:
2.
Inject the values shown in the table below and verify accuracy of the measured values. View the measured values in:
A2 METERING DATA\CURRENT METERING
INJECTED CURRENT
1 A UNIT
Ia = 0.78 A ∠0°
Ia = 3.9 A ∠0°
Ib = 1 A ∠113° lag
Ib = 5 A ∠113° lag
Ic = 1 A ∠247° lag
Ic = 5 A ∠247° lag
Ia = 1.56 A ∠0°
Ia = 7.8 A ∠0°
Ib = 2 A ∠113° lag
Ib = 10 A ∠113° lag
Ic = 2 A ∠247° lag
Ic = 10 A ∠247° lag
Ia = 0.39 A ∠0°
Ia = 1.95 A ∠0°
Ib = 0.5 A ∠113° lag
Ib = 2.5 A ∠113° lag
Ic = 0.5 A ∠247° lag
Ic = 2.5 A ∠247° lag
GE Power Management
): 600 V
pp
6
×
1.04 10
=
-------------------------- -
=
1000 A
×
3 600
∠
∠
I
=
1000 247° lag
c
∠
where a
1 120°
0.5
=
=
–
+
2
)
(
∠
)
(
∠
1000
113°
1 120°
–
+
1
∠
)
(
1000 233°
-- - 780 601.8
+
=
3
14%
EXPECTED NEGATIVE SEQUENCE
CURRENT LEVEL
5 A UNIT
489 Generator Management Relay
7.2 HARDWARE FUNCTIONAL TESTING
7.2.5 NEGATIVE SEQUENCE CURRENT ACCURACY
j 0.866
) 1000 113°
(
∠
)
)
j 798.6 601.8
j 798.6
–
+
–
–
1.04
600
1000A
MEASURED NEGATIVE SEQUENCE
14% FLA
28% FLA
7% FLA
)
CURRENT LEVEL
7-5
7
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