Thus, the insulating material must have high electrical resistance and possess moisture resistance. Insulation resistance – an important indicator of the quality of insulation of the transformer. Insulation materials must possess several other properties that ensure their long-term and reliable operation in the apparatus: heat resistance, mechanical strength, elasticity, flexibility, oil and water resistance and chemical resistance. On heat resistance insulating materials are divided into seven classes: Y, A, F, B, E, H, C (GOST 8865-70). For each class, set the maximum allowable heating temperature at which the material can be a long run.
Most insulation materials used in transformers oil belongs to the class A (Soaked or immersed in a liquid dielectric fiber materials of cellulose or silk, as well as other materials and combinations thereof), and their ultimate long-term allowable temperature of 105 C. To isolate coil wiring and outlets, as well as inter-layer winding insulation, and other devices use electrical insulating cable paper made from chemically treated wood pulp paper on special machines. It has a high electrical and mechanical strength, high resistance when working in hot transformer oil, is in heat resistance to a class A. Insulating papers are divided by type and thickness. Since January 1983, the transformers started to use a cable instead of electrical insulating transformer paper (GOST 16512-80) marks the T-080 T-120, TM-120, TMP-120, TV-120 and TSS-080 thickness of 80 and 120 microns. The letters in the paper marks mean: T – Transformer normal, B – High-voltage, M – multi-layer, P – hardened, and Y – compacted. Choose type of paper depends on the voltage class transformers. The paper is delivered in rolls of a width 500-1000 mm.