MA-041 – DGA 900 Plus - Installation & Commissioning Manual - Rev 1.1 4-Mar-22 Page 89 of 99
If the C1% measurement is above 5% after these checks, please contact GE customer
support team.
10.4.4 C.4 Tan δ (Power Factor) Measurement
To verify that the wiring is correct and that initial alarms levels are appropriate for the
system with instantaneous Tan δ measurements:
▪ Select BMT > Configuration as shown in Figure 10-24 to verify the ‘Exponential
Moving Average Configuration’. Ensure that:
− ‘Daily Moving Average Enable’ is Off
− ‘Moving Average Factor Phase Angle’ is 100 (factory default is 10000)
Figure 10-24: Exponential Moving Average Configuration
▪ Select BMT > Live Measurement as shown in Figure 10-25 to verify the ‘Measured
Phase Angle’. Ensure that:
− the measured angles are within 2
degrees of the expected angles. If the phase
angles are measuring more than 2
degrees, contact GE Technical Support for
further guidance. If applicable, check the same on secondary bushings.
− the imbalance (polar plot amplitude) for tan δ is less than 120%. If the tan δ is
more than 120%, the alarm limit should be adjusted. The alarm is recommended
to be set at 50% above the highest measurement. If applicable, check the same on
secondary bushings.
Figure 10-25: Measured Phase Angle
To change the Polar Plot PF % alarms:
▪ Select Alarm > Bushing Alarm Configuration > Primary Polar Plot PF% as shown
in Figure 10-26 to adjust the alarm as required for both Primary and Secondary
sources, High-High and High limits.
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