Insulating Materials

Insulating materials used for insulation of live parts of devices under different potentials from each other and grounded parts. Quality insulating materials ceteris paribus determines the service life of the transformer and is characterized by: a breakdown voltage, dielectric strength, dielectric loss, dielectric constant, high electrical resistance and other properties. Breakdown Ubr called the voltage at which breakdown occurs isolation if attached to the insulating material voltage and gradually increase it. Property insulation withstand voltage quantitatively express the electric field Ubr in which diaelektrik breaks, ie, the value of breakdown voltage per unit thickness of the dielectric (kV / mm). Breakdown voltage electric field at which the breakdown of the dielectric, it is called the dielectric strength, which is one of the main characteristics of the insulating material. The materials used in transformers are electric strength at 20 C from 5 to 90 kV / mm.

Insulation, located in an alternating electric field under the influence of AC a waste of electrical energy, which heats up. Absorbed energy called the dielectric losses. Quality check for the isolation transformer or separate parts of the application of high voltage, while in the isolation of an electric current, called leakage or conduction current, it depends on the electrical insulation of the transformer. Insulation resistance, denoted Rm3, measured and expressed in a megger or megaomah kiloomah (1 MW = 1 000 000 ohms, 1K = 1000 ohm) depends on the dielectric properties of insulating materials, as well as on external factors, temperature, moisture, and various contaminants. An increase in temperature and moisture especially sharply lower electrical resistance insulating material, and hence increase the leakage current and reduce the quality of insulation. Most of the insulating material has a large hygroscopic, ie, the ability to absorb moisture from the air, so after making or repairing transformers dried, resulting in resistance to their isolation increases.

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