Insulation systems for dry type transformers

The major role of the dry type transformer is to provide distribution of electrical power from indoor installations. They are used in preference to oil filled units by virtue of reduced fire hazards and the elimination of fire resistant enclosures. With increased use of electrical power for air conditioning, data processing, copying machines, higher illumination levels and automated equipment increased output is required, thus larger KVA units. As an electromagnetic device, the dry type transformer is generally noisy and is, therefore, frequently wall mounted near the ceiling to reduce the noise disturbance. Through the use of higher operating temperatures, increased output per unit size can be obtained to ease the requirements of wall mounting. A 150°C rise unit will require up to 50% less volume and 40% less weight than a Class A thermally rated unit of equivalent output. In other instances, such as ballasts for mercury vapor lamps, higher thermal performance is required because of higher ambient temperatures. The dry type transformer is also widely used by the Military, again for its increased output per unit size and elimination of fire hazards. It becomes, therefore, apparent that the key factor in their design, no matter what the application might be, is higher thermal capabilities.