How moisture reduces the life and performance of your transformer

MoistureinTransformerenlargeAs a practical matter, moisture accumulates in all transformer designs over the years. While a small portion is found in the oil, some 98 to 99 percent of it becomes diffused in the tons of paper (cellulose) insulation. Without moisture maintenance, every power transformer over 15 to 25 years of age can be expected to be “wet,” that is containing 2.5 to 5 percent of moisture by paper weight, or more. The potential for serious damage to the transformer at these levels of moisture is well known and traditionally the reason for dehydration. The paper becomes scarred by electrical phenomena that occur in the presence of moisture, such as flashovers between windings, treeing, and creeping discharges. Dramatic temperature changes can bring on the sudden migration of moisture to or from the paper insulation that give rise to the formation of “free water” (or “rain”) slowly draining to the bottom or water vapor rising to the top.


Increased Electric Risk:

  • Danger threshold: 2% to 3% moisture…transformer becomes increasingly exposed to electrical malfunction
  • Dielectric strength is determined by the level of moisture bound in the paper…the release of moisture…and overall condition of the paper
  • Moisture in paper contributes to weakening of aged paper by a variety of phenomena, including treeing, creeping discharges and spots of elevated moisture concentrations
  • Released water vapor and droplets create an instant and high vulnerability to substation anomalies-such as short circuits and lightening hits
  • The paper’s strength and its overall condition fundamentally determines the transformer’s reliability

Sources of Moisture:

  1. Residual after initial factory dry-out
  2. Ingress from atmosphere
  3. Aging decomposition of cellulose
  4. Aging decomposition of oil

We reserve the right to make changes to any described details and technical data contained herein without notice.  Continuous product enhancement by DryKeep® and local conditions may also result in deviations.