Substation Reliability Tip #04

Your Transformer Paper and Moisture

The Weakest Link in a Transformer

Most transformer failures are the ones we can see coming—if we’re looking at the right things. Moisture content is one of those measurable factors every transformer owner should look at, and it is a tremendously valuable predictor of failure. After more than five decades of servicing transformers, we’ve found that the weakest link in the system is where moisture loves to hide—the paper insulation.

The moisture content of the liquid insulation (the oil) is only a partial indicator of the amount of moisture in a transformer. The paper insulation has 100 times or more affinity for moisture compared to the oil. Moisture prefers paper over oil, which means the key to a dry transformer is keeping the paper dry.

This is important because the paper is the primary limiting factor to the life of a transformer. Moisture in the paper will accelerate the oxidation process. This will compromise the paper and weaken the ability of the unit to perform efficiently, decrease dielectric strength, increase the risk of flashover, and could eventually lead to failure. The paper’s lifespan is cut in half every time the moisture content doubles. And every year of delay in fixing the problem chips away at approximately two years of reliable service. Therefore, we like to say, “the life of the paper is the life of the transformer.”