GE 489 Portable Generator User Manual


 
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%==