The Insulation Material Determines the Operation Life of the Transformer to a Great Extent.
The reliability and service life of the transformer depends largely on the insulation used by the transformer. Insulating material is also called dielectric. It is a material with high resistance coefficient and low electrical conductivity.
Insulating materials can be used to isolate conductors of charged or different potential, so that the current is circulated in a certain direction. In transformer products, insulating materials also play the role of heat dissipation, cooling, supporting, fixing, arc extinguishing, improving potential gradient, moisture-proof, anti mould and protecting conductor.
Under the action of DC voltage, the insulating material is only passing through a very small current. Its resistance coefficient (refers to the volume resistance coefficient in air) is relatively high, generally in the 108~1020 ohm ˙ cm (the resistance coefficient of the conductor is 10-6~10-3 ohm ˙ cm, the resistance coefficient of the semiconductor is 10-3~108 &dot ˙ CM).
Insulation material has great resistance to the DC current, due to its high resistivity, the DC voltage, in addition to the surface of tiny leakage current, it is almost not conductive; and a capacitor current through the AC current, it is generally considered not conductive. The greater the resistivity of the insulating material, the better the insulation performance.
Generally, the insulating material is divided into three types:
1) gas insulation materials: under normal atmospheric temperature and pressure, the general dry gas has better insulation performance, such as air, nitrogen, hydrogen, carbon dioxide, six sulfur fluoride, etc. air and six sulfur fluoride are widely applied in transformers.
2) liquid insulating material: liquid insulating material is usually oil – like, also called insulating oil. Such as mineral oil, vegetable oil, synthetic ester and so on.
3) solid state insulation materials: such as insulating varnish, insulating adhesive, insulating paper, insulating cardboard, corrugated cardboard, electrician plastic and film, electrical laminate, rods, tubes, casting molded epoxy resin, electric porcelain, rubber and mica products.