Oil used in transformer
A transformer is an electrical device used to step up or step down voltage. During the process of stepping up or down the transformer heats up. To keep the transformer cool and insulated, transformer oil is used.
This type of oil is used for insulation and to keep the transformer cool. Also, the function of the oil is to stop corona discharge and arcing. In this article, we will discuss different types of oil used in oil immersed transformer.
Transformer oil uses
The main job of transformer oil is to increase winding insulation and to cool down the transformer. But transformer oil has some more uses as below:
- Oil increases insulation between coils and core. So this makes the size of the oil immersed transformer smaller than that of dry type transformer of the same power rating.
- Cooling down the transformer. Current passing through a coil or a conductor produces heat. And oil takes that heat and transfers it to the outside environment.
- Protecting bolts and metallic parts inside transformer tank against corrosion and oxidation.
- In case of any fault inside the transformer, oil analysis gives us a clear vision about the type of the fault. this is because the fault affect the oil chemical properties.
Cooling the transformer oil
As mentioned above the oil transfers heat out side the transformer. This is done by cooling methods as below.
- ONAN: Cooling: this is the basic cooling method. In this method oil and air are moved naturally. ONAN transformer cooling stands for Oil Nature, Air Nature. Oil moves inside the transformer by the nature flow as hot oil goes up and cold oil takes its place. Out side the body of the transformer the nature air flows and cool down it.
- ONAF : Oil Nature Air Forced. Using fans mounted on the body of the transformer heat is dissipated. While oil is natural flow.
- OFAF: Oil forced Air Forced. In this transformer cooling method oil is drawn by a pump, and air is forced by fans.
- OFWF: Oil is Forced by pump while Water is forced on the transformer body.
Types of oil used in transformer
There are two types of oil used in transformer. Mineral & Synthetic oil. We will discuss each type in detail.
Mineral oil
This type of oil is a petroleum product, different types of mineral oil are Paraffinic based and Naphthenic based. Talking about the Naphthenic based oils. This type of oil is the wax-free and better flowing feature. However proper heat distribution is one of its main disadvantages.
These type of oils is used for low-temperature. Similarly, the Naphthenic based transformer oil used in the method from paraffinic crude oil. Due to good viscosity, oxidation, and thermal durability feature, it is used for high temperatures also. The oxidation rate of Paraffin oil is lower than Naphtha oil, the sludge is an insoluble product it stays at the bottom of the tank. And as a result, it causes a problem for the cooling system of the transformer.
Synthetic Oil
This type of oil was more popular during the ’70s. The silicon-based oil was fire-prone. The disadvantages of this type of oil were moisture absorption and low heat dissipation. The use of this type was later on limited due to its cost.
Alternative to the oil used in transformers
We discussed different types of transformer oil. Each type has its pros and cons. However, there is always a substitute available in every field.The petroleum-based oil was used for a long time, but due to the high inflammability and less environment-friendly synthetic oil was introduced. Synthetic oil is fire-prone and is used where there is the risk of fire. However, now the use of the synthetic type oil is also limited. Dry-type transformers, synthetic esters, and Nano particles are used nowadays.
Tests of oil used in transformer
To determine the quality of transformer oil different tests are conducted on regular basis. These types of tests are listed below and we will discuss each in our upcoming topic. Dielectric Strength, Dielectric Dissipation Factor, Acidity,Oxidation Stability, Pour Point, Sludge Test, Flash Point, and many more types of tests are performed.
