# Properties of Good Transformer Oil

- Link: https://studyelectrical.com/2018/05/properties-of-good-transformer-oil.html
- Published: 2018-05-30T07:49:00+00:00
- Author: 

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 Even though the basic functions of the oil used
in transformers are heat conduction and electrical insulation, there are many other
properties which make a particular oil eminently suitable. Properties of good transformer
oil are explained in this article.  Organic oils of vegetative or animal origin 
are good insulators but tend to decompose giving rise to acidic by-products which
attack the paper or cloth insulation around the conductors.  Mineral oils are suitable
from the point of electrical properties but tend to form sludge. The properties 
that are required to be looked into before selecting oil for transformer application
are as follows:

### 1. Insulting property

This is a very important property. However, most of the oils naturally fulfill this.
Therefore deterioration in insulating property due to moisture or contamination 
may be more relevant.

### 2. Viscosity

It is important as it determines the rate of flow of the fluid. Highly viscous fluids
need much bigger clearances for adequate heat removal.

### 3. Purity

The oil must not contain impurities which are corrosive. Sulfur or its compounds
as impurities cause the formation of sludge and also attack metal parts.

### 4. Sludge formation

Thickening of oil into a semisolid form is called sludge. Sludge formation properties
have to be considered while choosing the oil as the oil slowly forms semi-solid 
hydrocarbons.

 

These impede flows and due to the acidic nature, corrode metal parts. Heat in the
presence of oxygen is seen to accelerate sludge formation. 

 

If the hot oil is prevented from coming into contact with atmospheric air sludge
formation can be greatly reduced.

### 5. Acidity

Oxidized oil normally produces CO₂ and acids. The cellulose which is in the paper
insulation contains a good amount of moisture. These form corrosive vapors. A good
breather can reduce the problems due to the formation of acids.

### 6. Flashpoint And Fire point

Flashpoint of an oil is the temperature at which the oil ignites spontaneously. 
This must be as high as possible (not less than 160º C from the point of safety).

 

Fire point is the temperature at which the oil flashes and continuously burns. This
must be very high for the chosen oil (not less than 200º C).

 

Inhibited oils and synthetic oils are therefore used in the transformers. Inhibited
oils contain additives which slow down the deterioration of properties under heat
and moisture and hence the degradation of oil. 

 

Synthetic transformer oil like chlorinated diphenyl has excellent properties like
chemical stability, non-oxidizing, good dielectric strength, moisture repellant,
reduced risk due to fire and explosion.

 

It is, therefore, necessary to check the quality of the oil periodically and take
corrective steps to avoid major breakdowns in the transformer.

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