Negative Sequence Current Accuracy - GE 489 Instruction Manual

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
a
The negative-sequence current Ins is calculated as:
1
2
-- - I (
I a I
= +
ns a b
3
1
-- - 780 0° ( ∠
=
3
1
-- - 780 0° ( ∠
=
3
141.2
= –
I
ns
⇒ ---------- -
%I
=
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
S2 SYSTEM SETUP GENERATOR PARAMETER
(Note: This is equivalent to setting FLA = 1000 A – For testing purposes ONLY!)
S2 SYSTEM SETUP CURRENT SENSING
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 Multilin
): 600 V
pp
6
×
1.04 10
-------------------------- - 1000 A
= =
3 × 600
∠ ∠
780 0°, I 1000 113° lag,
= =
b
) ∠
aI where a 1 120°
+ =
c
2
( ∠ ) ( ∠ )
1 120° 1000 113°
+ – +
∠ ∠ )
1000 127° 1000 233°
+ +
×
100 14%
=
GENERATOR RATED MVA: "
VOLTAGE PHASE-PHASE:
PHASE CT PRIMARY:
EXPECTED NEGATIVE SEQUENCE
CURRENT LEVEL
5 A UNIT
489 Generator Management Relay
7.2 HARDWARE FUNCTIONAL TESTS

7.2.5 NEGATIVE SEQUENCE CURRENT ACCURACY

∠
I 1000 247° lag
=
c
0.5 j0.866
= – +
( ∠ ) 1000 113° ( ∠ ) )
1 120°
1
-- - 780 601.8 (
j798.6 601.8
= – + –
3
1.04"
"600"
"1000 A"
MEASURED NEGATIVE SEQUENCE
14% FLA
28% FLA
7% FLA
(EQ 7.1)
(EQ 7.2)
(EQ 7.3)
)
j798.6
–
CURRENT LEVEL
7-5
7