GE 489

GE Power Management
489 Generator Management Relay 7-5
7 TESTING 7.2 HARDWARE FUNCTIONAL TESTING
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:
With the following output currents:
The negative-sequence current Ins is calculated as:
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:
1.04
S2 SYSTEM SETUP\GENERATOR PARAMETER\VOLTAGE PHASE-PHASE:
600
(Note: This is equivalent to setting FLA = 1000 A – For testing purposes ONLY!)
S2 SYSTEM SETUP\CURRENT SENSING\PHASE CT PRIMARY:
1000A
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 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
×
3600
×
--------------------------- 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– j 0.866+===
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– j 798.6 601.8– j 798.6–+
()
==
141.2–=
%
I
ns
⇒
I
ns
FLA
-----------
100
×
14%==