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GE Multilin 489 Generator Management Relay 7-5
7 TESTING 7.2 HARDWARE FUNCTIONAL TESTS
7
7.2.5 NEGATIVE SEQUENCE CURRENT ACCURACY
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
A
) = 1.04
Voltage Phase to Phase (V
pp
): 600 V
we have:
(EQ 7.1)
With the following output currents:
(EQ 7.2)
The negative-sequence current Ins is calculated as:
(EQ 7.3)
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 ÖØ GENERATOR PARAMETER Ö GENERATOR RATED MVA: "1.04"
S2 SYSTEM SETUP ÖØ GENERATOR PARAMETER ÖØ VOLTAGE PHASE-PHASE: "600"
(Note: This is equivalent to setting FLA = 1000 A – For testing purposes ONLY!)
S2 SYSTEM SETUP Ö CURRENT SENSING Ö PHASE CT PRIMARY: "1000 A"
2. Inject the values shown in the table below and verify accuracy of the measured values. View the measured values in:
A2 METERING DATA Ö CURRENT METERING
INJECTED CURRENT EXPECTED NEGATIVE SEQUENCE
CURRENT LEVEL
MEASURED NEGATIVE SEQUENCE
CURRENT LEVEL
1 A UNIT 5 A UNIT
Ia = 0.78 A ∠0°
Ib = 1 A ∠113° lag
Ic = 1 A ∠247° lag
Ia = 3.9 A ∠0°
Ib = 5 A ∠113° lag
Ic = 5 A ∠247° lag
14% FLA
Ia = 1.56 A ∠0°
Ib = 2 A ∠113° lag
Ic = 2 A ∠247° lag
Ia = 7.8 A ∠0°
Ib = 10 A ∠113° lag
Ic = 10 A ∠247° lag
28% FLA
Ia = 0.39 A ∠0°
Ib = 0.5 A ∠113° lag
Ic = 0.5 A ∠247° lag
Ia = 1.95 A ∠0°
Ib = 2.5 A ∠113° lag
Ic = 2.5 A ∠247° lag
7% FLA
FLA
P
A
3 V
pp
×
-----------------------
1.04 10
6
×
3 600×
--------------------------- 1000 A== =
I
a
780 0°, I
b
∠ 1000 113° lag, I
c
∠ 1000 247° lag∠== =
I
ns
1
3
---
I
a
a
2
I
b
aI
c
++() where a 1120°∠ 0.5– j0.866+===
1
3
---
780 0°∠ 1 120°∠()
2
1000 113°–∠()1120°∠()1000 113°∠()++()=
1
3
---
780 0°∠ 1000 127°∠ 1000 233°∠++()
1
3
---
780 601.8– j798.6 601.8– j798.6–+()==
141.2–=
%I
ns
⇒
I
ns
FLA
---------- -
100× 14%==