GE Multilin 489

7–6 489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 7: TESTING
7.2.4 Neutral Voltage (Fundamental) Accuracy
The specification for neutral voltage (fundamental) accuracy is ±0.5% of full scale (100 V).
Perform the steps below to verify accuracy.
Z In the
S2 SYSTEM SETUP ZV VOLTAGE SENSING menu, set:
NEUTRAL VOLTAGE TRANSFORMER: “Yes”
NEUTRAL V.T. RATIO: “10.00:1”
Z In the S2 SYSTEM SETUP ZV GEN. PARAMETERS menu, set:
GENERATOR NOMINAL FREQUENCY: “60 Hz”
Measured values should be ±5.0 V.
Z Apply the voltage values shown in the table and verify accuracy of the
measured values.
Z View the measured values in the
A2 METERING DATA ZV VOLTAGE
METERING
menu.
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:
Applied Neutral Voltage
at 60 Hz
Expected Neutral Voltage Measured Neutral
Voltage
10 V 100 V
30 V 300 V
50 V 500 V
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∠== =
Courtesy of NationalSwitchgear.com