SOLUTION

The magnetic core of the transformer is made up of laminated silicon steel. The silicon steel material is used to decrease the hysteresis loss. The thickness of the lamination varies from 0.3 to 0.5 mm. In order to reduce the eddy current losses, the thickness of laminations should be very small. The laminations are insulated from each other by using insulation like varnish. When requiring a varnish for a winding application, bond strength, application, build (thickness), temperature class and chemical resistance must be determined.

The purpose of providing the coating of varnish in windings are

• Bonding the magnet wire together to form a hard structure, which provides a degree of mechanical strength.
• Adding additional insulation to the winding system preserves the initial dielectric strength of the insulation to which it is applied.
• The extra insulation allows the winding to withstand higher voltage stress levels without damage.
• Sealing the winding to resist contaminants such as moisture, dust, fungus, and chemicals.
• Filling the voids (displacing the air – that is, a thermal barrier) in the slots of electrical apparatus, between layers of insulation and winding turns.
• To promote the conduction of heat from the center of windings to the exterior environment via a low thermal resistance path and so keep the winding temperature down.
• A reduced winding temperature means lower electrical resistance and therefore less copper (I²R) losses.
• To reduce mechanical vibrations and the audible noise level of the apparatus.