5 negative sequence current accuracy, Negative sequence current accuracy -5 – GE 489 User Manual
Page 217
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
Ч
-----------------------
1.04 10
6
Ч
3 600
Ч
---------------------------
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
1 120
°
∠
0.5
–
j0.866
+
=
=
=
1
3
--- 780 0°
∠
1 120
°
∠
(
)
2
1000
113
°
–
∠
(
)
1 120
°
∠
(
) 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
Ч
14%
=
=