Water kills electrical transformers, This is why we use moisture protection like transformer breathers and Nitrogen blankets.
In this article, let’s go into deep detail to discover everything about moisture in transformer oil. I made a deep search about this topic, And I will answer the important question that I found.
Table of Contents
Can Transformers Get Wet, and Why?
Yes, transformers can get wet, One of the largest transformers in my work was too hot, By doing deep analysis and investigating, we discovered that the oil has water, But how did this water get into the oil tank? Moisture can enter the transformer tank from the outside environment as follows:
- Through the breather, during the breathing-in process, if the silica gel is not fresh.
- Also, if the transformer has any other holes or openings, then moisture can enter through.
- During oil replacement, if the new oil has moisture contaminates.
While the amount of moisture in a transformer depends on many factors, and can only be detected through oil testing and analysis.
Moisture isn’t always in the oil, it also can hide well in the other insulation between coils and the core. Where exactly? Let’s find out that.
Where Does Exactly Moisture Stay?
A transformer has two insulation types, one is solid and the other is liquid. For solid insulation, plant cellulose is used which originally contains around 5 percent of water, and undergoes a certain drying process to bring this level down to less than 1 percent.
The water content in the insulation keeps changing in both these insulators throughout the transformer’s lifetime, based on the temperature and external moisture.
In normal cases, most of the water remains in the solid insulation, but when the temperature rises from its base value, water starts flowing from cellulose to oil.
The state of solubility of water in oil largely depends on temperature. Data suggests that at 10 degrees Celsius, water solubility remains at 36 ppm, which could go up to 600 ppm at 90 degrees Celsius.
How Moisture Reduces The Life of Transformers?
How to Protect Transformer Oil From Moisture?
Methods to Discover Water in Transformer Oil
Initially, the water gets absorbed by the cellulose insulation, and with the increase in temperature, the moisture continues to flow in the oil.
Therefore, regular testing and monitoring is a way to protect transformer oil from moisture. For measuring the water content in the transformer, either of the two methods can be used i.e. drew point analysis and water in-oil analysis.
- Drew Point analysis: This method measures the saturation point of the air and assesses the dew point temperature. The dew point temperature actually determines the threshold and air needs to be cooled at this point under a constant level of pressure. By achieving this point, the air will no longer be able to absorb any more water in the form of gas.
- Water-in-oil analysis: This method actually detects the amount of water in oil by various methods. “Karl Fischer Coulometric Titration” method is the most popular one and measures the amount of iodine required for titration of the oil sample. Another method is the “Visual crackle test”, which is very subjective and can’t determine the actual quantity of water.
Once the detection of water is done, any of the two methods i.e. Hot Oil flush and Hot oil spray can be used to dry the transformer.
In the Hot Oil Flush treatment, the hot oil is pressed through a filter made of paper elements. That filter is sprayed on the transformer coil, which absorbs any kind of moisture from the coil assembly.
In comparison to that, the hot oil spray method involves spraying hot oil on insulation and sucking up the air surrounding the insulation.
Heat present in hot oil causes water to evaporate, which is collected by the suction of a vacuum. While the Hot oil spray method is more popular, the Hot oil flush method is easy and can remove a great amount of moisture from the transformer.