GE Multilin g60

GE Multilin G60 Generator Protection System 10-9
10 APPLICATION OF SETTINGS 10.1 SETTING EXAMPLE
10
c) THIRD HARMONIC NEUTRAL UNDERVOLTAGE
If the phase VTs are delta connected then third harmonic voltage cannot be measured and the 100% stator ground element
cannot be used. In this case the third harmonic neutral undervoltage element can be used. Field measurements should be
taken over the entire operating range of the machine to determine the variation of the third harmonic voltage as shown
below:
Figure 10–3: THIRD HARMONIC NEUTRAL UNDERVOLTAGE FIELD MEASUREMENTS
The element is accurate for levels as low as 0.25 volts, secondary. In this case, the pickup setting will be:
(EQ 10.31)
The third harmonic will dip below the pickup setting between 85 and 105 megawatts. The element should be blocked over
this range. A margin of 5% should be added to the relay settings. The values for maximum and minimum power will be:
(EQ 10.32)
(EQ 10.33)
Voltage supervision will be given a setting of 0.8 pu in order to prevent maloperation during a sustained undervoltage con-
dition. A time delay of 5 seconds will be applied. If required, the element may be blocked when the machine is offline. Make
the following changes in EnerVista UR Setup or through the
SETTINGS  GROUPED ELEMENTS  SETTING GROUP 1 
STATOR GROUND  3RD HARM NTRL UNDERVOLTAGE menu:
830733A1.CDR
Megawatts
Third harmonic
neutral voltage
PICKUP
0.25 V
240 V
----------------- 0.001 pu==
Max Power 1.05
105 10
6

3 8000 157.5 66
---------------------------------------------------------
 0.441 pu==
Min Power 0.95
85 10
6

3 8000 157.5 66
-------------------------------------------------------- -
 0.323 pu==