What are different types of Insulations used in Transformer?

There  are two types of Insulations used in Transformers:

 1) Oil

 2) Solid Insulation

What are the Functions of Transformer Oil ?

Transformer Oil has mainly three Functions:

  1) Insulation

 2) Cooling

3) Also, there is contamination caused by Chemical Interactions with Windings and other Solid Insulations, catalyzed by high operating Temperatures, in the form of Gases. So apart from providing insulation and cooling,  the presence of Gases in Transformer Oil  provides vital information about the health of the Transformer Insulation. Detection of the Fault at early stages, saves the Transformer from Failures.

What are the different types of Transformer Oils?

If Inhibitors are added ( in the range of 0.08 to 0.4) to the Oil, it boosts the Dielectric Strength of the Oil by increasing its Oxydation Stability. Based on the use of Inhibitors, Mineral Oil can clssified into:
1) Inhibited
2) Partially Inhibited
3) Unhibited

There are two types of Oils viz:
1) Mineral Oil
2) Easter Oil

There are two types of Minerals Oils used in Transformer viz:
1) Praffin based
2) Napthenic based

In Paraffin Oil, though the Oxidation rate is lower, than that of the Napthenic Oil, the oxidation product or the sludge is insoluble and precipitated at the bottom of the tank, therby obstructing the Transformer Cooling system. Still it is highly used in India, due to its high availability. It has a high Pour Point, which is a disvantage in other Countries, but not so much of a problem in India.

Napthenic oil is more easily oxidized than the Paraffin oil.But, the Oxidation product (Sludge) is more Soulble than the Paraffin Oil. Hence, it is Good for Transformer as it improves, oxidation stability.

Napthenic Based Oil cannot be topped up with a Prafannic Based Oil. Because their properties and composition are totally different and it will effect the Cooling of the Transformer, as the two Oils wont mix.
Because in Parafinic Based oil, the contents of Paraffin are very high.
In Naptahanic Based Oil, the Prafinic and Napthenic Contents are almost equal.

If Napthenic Based and Praffinc Based Oils are to be combined and used, we need to carry out a Compatibility Test.

Ester Oil:
It is 3 to 4 times costlier that the Mineral Oil, but the cost factor is overcomed by Overloading the Transformer and not using firefighting Systems.

What is Solid Insulation ?

 Cellulose material (Paper, pressboard) with Class-A Thermal Index (105 deg C) is usually employed as Solid Insulation in the Transformer. It covers the Windings.
When impregnated with Oil, it acts as an excellent Insulator.
It has a High Dielectric Strength, compatible with Transformer Oil. It also, has high Electrical Surface Resistance and high Permittivity.

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