Diagnosing and solving gassing issues on wind farm transformers

January 18, 2018

In the late 1980s, wind farms were built in nearly every state to accommodate the country’s focus on developing its renewable energy resources. In recent years, there has been renewed emphasis in the U.S. to increase its renewable energy output and reduce its overall carbon footprint.

This presents a challenge because 20 to 30 percent of padmounted transformers in service at wind farms across the country are generating dangerous levels of combustible gasses. The combustible gasses in these transformers are causing reliability issues for wind energy producers. These transformers require inspection, testing and possible removal from service, which can cause interruption in energy produced from that particular wind turbine. Transformers that exhibit gassing may require repair or replacement. The wind farm is then at risk due to a possible lack of operational replacement transformers.

Gasses in wind energy transformers

Because the wind doesn’t blow consistently, or sometimes at all, there are constant changes in the energy supply. The high-efficiency generators must convert and condition the power prior to transmission. Wind energy pad mount transformers are a vital link in this process. The percentage of wind energy transformers exhibiting combustible gassing issues is more than triple that of normal utility distribution transformers.

The presence of high levels of gasses can cause different problems for transformers.

  • Hydrogen – partial discharge in oil
  • Methane – high heat
  • Ethane – high temperature hot spots
  • Ethylene – overheating of contacts or connections
  • Acetylene – arcing, which always bears investigation
  • Carbon monoxide – aging of cellulose insulation
  • Carbon dioxide – general overheating

Any of these can be troublesome for your transformer, which can result in safety issues, failures, equipment damage, unplanned downtime and costly, premature equipment replacement.

Leading the way in influence and innovation

Solomon Corp is at the forefront to provide solutions to the challenges facing the wind energy industry when it comes to transformers. We have more than 15 years of experience testing, evaluating, root cause analysis and repairing wind farm transformers.

Ken Puetz, Solomon Corp’s Director of Engineering, provided his expertise in transformer redesign and testing at the 2017 American Wind Energy Association’s Operations, Maintenance and Safety Conference in San Diego, California. The premier conference for wind farm operators in the U.S., the event has grown in popularity and attendance every year since the first event more than 10 years ago.

“One of the biggest problems facing the wind energy industry is the absence of acceptable guidelines,” said Ken. “There is no standard for this class of transformer.”

Ken is an active member of the Doble Engineering Transformer Sub Committee which addresses wind farm gassing issues. The Sub Committee has been gathering historical data on wind farm gassing, failure and OEM manufacturing standards. It is putting together recommendations for an IEEE Standards Committee on developing industry standards for wind farm transformers.

The processes for sampling and testing of transformer oil for combustible gasses follows several ASTM methodologies and the guidelines normally used for analysis are from IEEE C57.104. The guide specifically states that the table for recommended action does not apply to this type of transformer. A wind farm transformer developing combustible gasses runs the risk of an internal explosive failure. The interpretation of combustible gas analysis reports is subjective, which can affect determining when a gassing transformer should be removed from service and either repaired or replaced. These guidelines are not clearly defined in the industry.

Solomon Corp utilizes years of combustible gas report analysis experience and evaluating wind farm transformer failure to help wind farm maintenance mangers make informed decisions when dealing with inspection, testing, and removal from service. This experience and expertise has lead Solomon Corp to develop its own repair and manufacturing standards for wind farm transformers.

Solomon Corp has adopted design and manufacturing standards for wind farm transformers that include:

  • Minimum K=4 rating for to prevent heating associated with harmonic heating
  • Electrostatic shielding between HV and LV windings to limit harmonics passing through transformer and onto the HV system
  • Minimum 200kV BIL (Basic Insulation Level, for surge and peak load handling capabilities) on coil design
  • Improved HV lead assembly including standoffs and clearances for 200 KV BIL
  • Reduction in core flux density to prevent core heating from over excitation up to 115 percent of nominal voltage
  • Improved core grounding to reduce electrical stresses between HV winding and core from core lamination capacitance voltage development
  • Three-leg core design, if possible, to further reduce electrical stresses between HV winding and core laminations

Short-term and long-term solutions to solve gassing issues

Some wind farm companies choose to allow gassing transformers run to failure because of reduced maintenance budgets and limited number of spare transformers. Others are evaluating the current gassing transformers and systematically replacing or repairing the most critical transformers as their maintenance budgets allow.

Preventative maintenance is a better short-term option than run to failure. This can include:

  • More frequent DGA testing of transformers developing combustible gasses to monitor the rate of increase and encourage development of a corrective action plan
  • Proactive de-gassing the transformer to reduce combustible gas levels and reduce the risk of an explosive failure
  • On-site inspection and testing to further assess the condition of transformer and necessity for corrective action
  • Removal and repair of combustible gassing transformers with design and manufacturing standards for wind farm transformers.

When it’s on the line

Solomon Corporation is taking the lead in the diagnostics, repair and replacement of aging wind farm transformers. We can provide diagnostic services, on-site inspection, testing and maintenance options. Solomon Corp can pick up your wind farm transformer that has failed or is developing combustible gasses and repair it to our specifications or provide a replacement unit from our inventory.

For more information or to request a quote, visit us at www.solomoncorp.com or call 800-234-2867.