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an hour the transformer was switched off and again
charged from the high voltage side at 10:30 am on
04/06/2019. It was decided to run the transformer at
no load for nearly 24 hours.
Finally, on 05/06/2019 at 5:27 am the power transformer
was put into load.
Figure 6: Arrangement for Shorting of the Three CONCLUSION
Windings at Tap No.-5
This paper documents the knowledge & expertise,
➤ The bypassed floating collector rings were kept gathered during repair of OLTC at site and making the
shorted with the neutral point to prevent any transformer recommission, which was looking very
induced voltage or partial discharges. The damaged unlikely, at one time, since these type of repairs are very
moving contacts for the selector chamber of the tap rare in site.
changer were kept disconnected.
By this time the team had become experts in repair of
➤ After completion of all the above rectification OLTC at site. Using this knowledge, the recent similar
jobs, the insulation resistances were measured by type of fault, generated for transformer at another site
applying 5 kV DC Voltage across the windings and (Prinsep Street S/S T-4) had been rectified very quickly
the results were found satisfactory. and smoothly.
➤ Oil was topped up and after proper air release, ACKNOWLEDGEMENT
this time, apart from all the routine tests, 30 kV
DC Voltage was applied across all the three high Special thanks to Mr. Rajarshi Ghosh (General Manager,
voltage windings and the test results obtained were S/S), Mr. Jaideep Basu Roy (Deputy General Manager,
satisfactory. S/S) and Mr. Kishore Kumar Chakraborti (Sr. Manager, S/S)
for their continuous support and valuable suggestions
➤ Subsequently, online oil filtration was carried out during pinpointing of vital root causes of the fault and
to remove the gases from the transformer oil for its corresponding necessary rectification jobs. Apart
48 hours. After that DGA test was carried out on oil from them, the authors gratefully acknowledge Mr.
samples and the result obtained was satisfactory. Koushik Chowdhury (Deputy Manager) Mr. Sujit Saha
(Refer Table-I) (Junior Engineer) for executing the field job along with
his team.
➤ After ensuring proper electrical primary connections
for the above transformer, clearance for charging the REFERENCES
power transformer was given.
[1] Herbert G. Erdman (ed.), Electrical insulating oils,
➤ Initially, the transformer was charged from low ASTM International, 1988 ISBN 0-8031-1179-7, p. 108
voltage side at 09:45 am on 04/06/2019 at tap no.-
5. And the plant behaved normally. After about half [2] “DISSOLVED GAS ANALYSIS OF MINERAL OIL
INSULATING FLUIDS”. Retrieved November 2, 2011.
[3] “Dissolved Gas Analysis”. 2005 [last update]≤. Retrieved
November 21, 2011
27
charged from the high voltage side at 10:30 am on
04/06/2019. It was decided to run the transformer at
no load for nearly 24 hours.
Finally, on 05/06/2019 at 5:27 am the power transformer
was put into load.
Figure 6: Arrangement for Shorting of the Three CONCLUSION
Windings at Tap No.-5
This paper documents the knowledge & expertise,
➤ The bypassed floating collector rings were kept gathered during repair of OLTC at site and making the
shorted with the neutral point to prevent any transformer recommission, which was looking very
induced voltage or partial discharges. The damaged unlikely, at one time, since these type of repairs are very
moving contacts for the selector chamber of the tap rare in site.
changer were kept disconnected.
By this time the team had become experts in repair of
➤ After completion of all the above rectification OLTC at site. Using this knowledge, the recent similar
jobs, the insulation resistances were measured by type of fault, generated for transformer at another site
applying 5 kV DC Voltage across the windings and (Prinsep Street S/S T-4) had been rectified very quickly
the results were found satisfactory. and smoothly.
➤ Oil was topped up and after proper air release, ACKNOWLEDGEMENT
this time, apart from all the routine tests, 30 kV
DC Voltage was applied across all the three high Special thanks to Mr. Rajarshi Ghosh (General Manager,
voltage windings and the test results obtained were S/S), Mr. Jaideep Basu Roy (Deputy General Manager,
satisfactory. S/S) and Mr. Kishore Kumar Chakraborti (Sr. Manager, S/S)
for their continuous support and valuable suggestions
➤ Subsequently, online oil filtration was carried out during pinpointing of vital root causes of the fault and
to remove the gases from the transformer oil for its corresponding necessary rectification jobs. Apart
48 hours. After that DGA test was carried out on oil from them, the authors gratefully acknowledge Mr.
samples and the result obtained was satisfactory. Koushik Chowdhury (Deputy Manager) Mr. Sujit Saha
(Refer Table-I) (Junior Engineer) for executing the field job along with
his team.
➤ After ensuring proper electrical primary connections
for the above transformer, clearance for charging the REFERENCES
power transformer was given.
[1] Herbert G. Erdman (ed.), Electrical insulating oils,
➤ Initially, the transformer was charged from low ASTM International, 1988 ISBN 0-8031-1179-7, p. 108
voltage side at 09:45 am on 04/06/2019 at tap no.-
5. And the plant behaved normally. After about half [2] “DISSOLVED GAS ANALYSIS OF MINERAL OIL
INSULATING FLUIDS”. Retrieved November 2, 2011.
[3] “Dissolved Gas Analysis”. 2005 [last update]≤. Retrieved
November 21, 2011
27
