Insulating Materials for Transformers

Apart from active materials such as copper and grain oriented silicon steel, power transformers use a large number of ferrous, non-ferrous and insulating materials. It is important to use suitable insulating materials to make optimal use of these materials based on their electrical, mechanical, physical, chemical and thermal properties. The insulation grade of a power transformer depends on the test level that the insulating material can withstand.

Transformer insulation is based on the basic impulse insulation level and the rated voltage. The insulating medium in transformers up to 11KV mainly consists of paper wrapped around the transformer coil conductor, mineral oil and cardboard used to isolate the coil from the ground. One basic requirement for all insulating materials is that they should be compatible with insulating oil and should not react with the oil. The types of materials used for insulation and their applications are as follows:

1. Insulating Oil: Insulating oil plays a very important role in the transformer insulation system. In low voltage transformers, for example, transformers used in the 12-1000V range or low power rated transformers do not require insulating oil. The heat dissipation of low voltage transformers is very low. In 11KV transformers, insulating oil has an important rule as an electrical insulator as well as a coolant for heat dissipation losses. Transformer oil is basically obtained by fractionation and subsequent treatment of crude oil. Thus, transformer oil acts as a liquid dielectric and coolant and is placed in the tank where the transformer core is placed.

2. Insulating paper: Paper is a fabric made of plant fibers that is felted to form a web or sheet. The fiber raw material comes from plants such as cotton, hemp, abaca, straw and conifers. It can achieve very high electrical strength values ​​when immersed in vacuum oil."Medium permeability process insulating paper" is used for layer winding insulation, oil-immersed bushing capacitor cores."High permeability process insulating paper" is used to cover rectangular copper conductors and continuously transposed copper conductors."Corrugated kraft paper" is used to cover the flexible copper cable insulation layer of the winding leads."Pressed paper" is used as the backing paper for axial cooling tubes.

3. Insulating paperboard: Paperboard is a widely used insulating material that can be used to manufacture various components used in the electrical, mechanical and thermal design of transformers. Paperboard is also made from plant fibers, which contain a large amount of cellulose in their cells. The most difficult practical insulation in power transformers occurs at the winding ends and winding lead-outs.

Moulded cardboard parts can be made into any desired shape. Angle rings and caps are widely used mouldings. There are many types of cardboard used in high voltage transformers, but "soft cardboard laminates" are used as washers, terminal gear clamps and brackets, and spacers in 11KV transformers, etc. "Paperboard mouldings made of wet board or wet wood pulp" are used for angle rings, caps, sectors, nozzles, square tubes, lead-outs, for insulating winding ends, insulation between windings, and many other applications.

4. Wood: Wood laminates are made of veneers selected from various woods. The veneers are dried and partially or fully impregnated with natural phenomena. In areas where higher mechanical strength and lower electrical strength are required, dense laminated wood is used to make various insulating parts such as coil clamping rings, clamps, brackets, cores and yokes, etc.

5. Insulated Copper Conductors for Windings: Different types of insulated copper conductor windings are used in power transformers such as Paper Wrapped Rectangular Copper Conductors, Double Paper Wrapped Bundled Rectangular Copper Conductors, Paper Wrapped Continuously Transposed Copper Conductors, Double Transposed Copper Conductors Bundled, Double Rectangular Copper Conductors Bundled with Common Paper Strip Provided Between Two Conductors and Epoxy Coated Continuously Transposed Conductors. These are used for space factor and mechanical strength of windings. "Paper Wrapped Rectangular Copper Conductors" are used to make different types of windings."Paper Wrapped Standard Copper Cables" are used to make leads and terminals."Corrugated Paper Wrapped Flexible Copper Cables" are used to make leads and terminals that need to be bent into small radius."PVC Insulated Copper Cables – Single and Multicore" are used for control wiring in distribution boxes, nitrogen, sealed systems.

6. Insulating Tapes: Insulating tapes are used for various tape purposes. Such as cotton tapes, cotton newar tapes, glass braided tapes, braided tapes and phenol laminated paper base sheets. These tapes are used for taping, bundling, insulation of core bolts, where high strength is required and bundling of transformer cores.