Insulating Supplies Utilized in Transformers

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Insulating supplies used in transformers
Up to date on August 28, 2014 OSBERT JOEL C moreContact Creator Learn more on transformers

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Testing of transformers

Cooling of Transformer

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Insulating supplies utilized in transformers

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Insulation is one among an important constituent of a transformer. The durability and stability of the transformer depends upon the right utilization of insulating materials in it. In transformers mainly three insulating supplies are used.

Transformer oil

Insulating paper

Press board
Of the three, the most important insulating material used is transformer oil.

Transformer oil
Transformer oil
As stated earlier transformer oil is the most important insulating material utilized in transformer. It is among the essential factors that decide the life and passable operation of the transformer.

The transformer performs the following two capabilities.

1. It supplies insulation together with the insulating materials used within the conductors and coils.

2. It additionally acts as a coolant to extract heat from the core and the windings.

Transformer makes use of hydrocarbon mineral oil. It mainly consists of 4 generic classes of organic compounds. They’re aromatics, paraffins, napthenes and olefines. Transformer oil will present higher insulation when aromatics, paraffins, napthenes and olefines are present in it at a proper proportion. Transformer oil is desired to have more of saturated paraffins and fewer of aromatics, napthenes and olefines for higher insulation. For extra stability, more aromatics and napthenes are necessary. To get transformer oil at insulating property and stability, there have to be an optimum mix of four natural elements. This can be obtained by careful refining of crude oil. Vegetable and animal oils cannot be utilized in transformers as a result of they type fatty acids and assault the fibrous insulating supplies.

The transformer is affected by its operating situations. The presence of moisture or suspended particles in transformer oil affects its dielectric property. Hence transformer oil it must be tested periodically. If the oil is containing moisture or suspended particles it ought to be filtered or replaced by recent oil.

Bodily constants of Transformer oil

Permitivity 2.2

Thermal conductivity 0.12 W/m deg C

Particular Heat 2.06 kJ/kg deg C

Co-efficient of Growth 0.00078/ deg C

Imply density issue zero.00065/ deg C
The above parameters are primarily based on IS 335 Insulating paper
Insulating paper is made from the vegetable fibers. These fibers primarily consist of cellulose. The primary properties of these papers are listed below:


Grammage is the ratio of mass to the area. It influences many of the electrical and mechanical properties. The advisable worth for 125 micrometer thick paper is 100 gm/mt2.The maximum allowable variation is 5%.


The paper really helpful in transformer use can have a density vary of 0.6 to 1.3 gm/c.c.

Moisture content material

Moisture content reduces the dielectric property of the paper. Since paper is hygroscopic, moisture ingression takes place with utilization. The maximum allowable moisture content material is 8%.

Oil and water absorption

The dielectric property of paper increased when impregnated in oil underneath vacuum and decreases with water content material. Regardless that the water content material is just not advisable the maximum permitted water content material is 10%.

Air permeability

Permeability is the rate at which the air can cross by way of it. The dielectric power of paper is inversely proportional to the air permeability. The beneficial worth of air permeability is 0.2-zero.5.

Tensile strength and elongation

Paper should be capable of withstand the tension throughout wrapping. Recommended worth of tension is 78 – 85 N-mt/gm in wrapping direction and 25 – 30 N-mt/gm.

The electrical parameters of insulating paper are indicated under.

Property Recommended Value

Break down voltage 7- 7.5 kV/mm (min) at ninety deg. C

Dissipation issue zero.003 (max)

Conductivity 10 ns/mt (max)
Press board
Press board is also made up of vegetable fibers and accommodates cellulose. Stable press board unto 6 mm to 8mm thick is ordinarily made. Since probably the most difficult insulation drawback in HT transformer occur at the ends of the windings and lead outs from the windings hence moulded pressboards are broadly utilized in these elements for insulation. Synthetic resin bonded paper based mostly laminates are utilized in voltage burdened zones. The necessary parameters considered are density, tensile strength, elongation, conductivity, oil absorption, moisture content, compressibility and many others.

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What are the type of insulators used in transformer windings

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Great WORK