10MV+A Transformer DGA High Hydrogen Level

[sparkee]

Two new oil filled 10MV·A transformers 44kV/4.16kV were installed connected to the same source. After two years DGA indicated very high hydrogen levels in one of the transformers (>20,000ppm). Methane>1900, Ethane>200, Carbon Dioxide>1000. A Radio Interference Voltage test by the transformer manufacturer at 200% of rated voltage showed an increase from 5 microvolts to more than 500 microvolts. The other transformer DGA results were normal. There is no indication or record of unusual events during the two years of operation, loading has been less than 5MV·A per transformer.
What is the likely cause of the problem? What can be done to prevent such an occurrence?

 

[jghrist]

See DISSOLVED GAS ANALYSIS OF MINERAL OIL INSULATING FLUIDS Written by: Joseph B. DiGiorgio, Ph.D

http://www.nttworldwide.com/tech2102.htm

Also
IEEE guide for the interpretation of gases generated in oil-immersed transformers
IEEE Std C57.104-1991

Abstract:
Detailed procedures for analyzing gas from gas spaces or gas-collecting devices as well as gas dissolved in oil are described for use in power transformers. The procedures cover: (1) the calibration and use of field instruments for detecting and estimating the amount of combustible gases present in gas blankets above oil, or in gas detector relays; (2) the use of fixed instruments for detecting an determining the quantity of combustible gases present in gas-blanketed equipment; (3) obtaining samples of gas and oil from the transformer for laboratory analysis; (4) laboratory methods for analyzing the gas blanket and the gases extracted from the oil; and (5) interpreting the results in terms of transformer serviceability. The intent is to provide the operator with positive and useful information concerning the serviceability of the equipment. An extensive bibliography on gas evolution, detection, and interpretation is included

 

[jbartos]

Suggestion: Visit

http://www.usbr.gov/power/data/fist/fist3~30/3~30_con.htm

for: parameters (see section 4.6):

 

[sparkee]

Thanks to both jghrist and jbartos. Both suggestions were helpful.