MA-025
–
DGA 900 Operator Guide
–
Rev 2.0
12-Apr-19
Page 87 of 92
Appendix E
Alarm Settings: General Advice
Note: This Appendix is based on Technical Bulletin No 18 (amended below for DGA 900).
E.1
Introduction
There are published standards for interpretation of DGA results. The main internationally
recognised standards are IEEE® C57.104 and IEC® 60599. It is recommended that the
customer refers to these or local standards for more information on DGA interpretation.
As every transformer is different due to design, manufacturing tolerances, operating
regime, etc., there are no rules that can be applied to every transformer. Therefore, alarm
settings should be individually set for each transformer.
IEEE C57.104 provides a 4-level criterion to classify risks to transformers. Condition 1 gives
the av
erage gas values below which a ‘
normal transformer
’
is operating satisfactorily.
If there is DGA history available for the transformer, then the customer should also consult
this information when deciding on the alarm settings for the transformer.
E.2
Setting Alarms
All online DGA monitors should have alarm levels set at commissioning. This will ensure
that the customer is alerted should the gas concentrations increase. While it is the
customer’s responsibility
to set appropriate alarms, it is recommended that there always
be some alarms set on the DGA monitor as there have been some cases where alarm
levels have not been set and the transformer has failed without any notification to the
customer.
Customers with experience in monitoring transformers may have their own methodology
for setting alarms. In this case, the customer methodology should be used to set alarms on
the DGA monitoring system.
Where a customer wishes to monitor the transformer for a period before deciding on the
alarm settings, it is recommended that some preliminary alarm levels are set at the time of
commissioning using the method outlined in E.3.
E.3
Main Tank: Gas Level Alarms
If the customer does not have their own system for setting alarms, the following procedure
may be used, at the customer’s discretion, to set preliminary
alarms on the DGA monitor:
•
Run the analyser for several hours, preferably overnight, at hourly measurements.
•
Compare the results to IEEE Standard C57.104-2008 to see if any of the results are
outside the established norms.
