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August 2011

Hydrogen Sources Within a Transformer System

By Lance Lewand, Director Insulating Materials Laboratory

The presence of hydrogen in transformer oil tested by dissolved gas-in-oil analysis (DGA) is traditionally associated with partial discharge (PD) activity. However, hydrogen can also be produced by several other sources. One example is electrolysis of water in the drain valve. This situation has nothing to do with the operation of the transformer, but can influence the production of hydrogen unless procedures are taken to guard against it - especially in the sampling technique.

Hydrogen can also be produced from the overheating of the oil between core laminations. This condition can be difficult to distinguish from PD activity. However, this can be accomplished by using the right PD sensing tools.

Stray gassing, catalytic reactions involving stainless steel, and breakdown of passivator compounds are also conditions that produce hydrogen. They may indicate an incipient fault is present in the transformer when it is really a byproduct of collateral processes not associated with the actual operation of the transformer. All of these conditions need to be monitored and on-line monitoring may be required in certain cases.

DGA analysis itself may be responsible for the reporting of hydrogen where none exists. There is another gas, helium, that is used as a leak check gas for transformer repairs. It can be confused with hydrogen if the laboratory is unable to separate the two components or if the chemist performing the test is inexperienced and unable to determine the difference between the two gases. A recent Doble conference paper addressed these situations in detail.

The links below provide for more information on the topics discussed in this article.

• Dissolved gas-in-oil analysis (DGA)
   
• Sampling Technique
   
• Partial Discharge (PD) Sensing Tools:
  PD Services
  PD Products
   
• Stray Gassing:
  The Gassing Characteristics of Transformer Oils at Modest Temperatures
  Part 1: Transformer Experiences
  Part 2: Laboratory Experiments
   
• Doble Client Conference Paper: 
  Case Studies Involving Insulating Liquids and Materials from the Doble Materials Laboratories
  

Lance Lewand has been with Doble since 1992 and is the Director of the Insulating Materials Laboratory. He has been a member of ASTM D-27 since 1989 and has published numerous technical papers pertaining to sampling and testing of electrical insulating materials and laboratory diagnostics. Lance earned his B.S. degree from St. Mary's College of Maryland.