Temperature rise in Transformers

Temperature rise in Transformers

Losses dissipated in transformers in the core and windings get converted into thermal energy and cause heating of the corresponding transformer parts. The heat dissipation occurs as follows: i) from the internal heated parts to the outer surface in contact with oil by conduction ii) from oil to the tank walls by convection and iii) from the walls of the tank to the atmosphere by radiation and convection.

Q = Power loss(heat produced ), J/s or W

G = weight of the active material of the Machine, kg h = specific heat, J/kg-◦C

S = cooling surface area, m2

λ = specific heat dissipation, W/ m2 -◦C

c = 1/ λ = cooling coefficient, m2 -◦C / W

θm = final steady temperature rise,◦C

The temperature of the machine rises when it is supplying load. As the temperature rises, the heat is dissipated partly by conduction, partly by radiation and in most cases largely by air cooling. The temperature rise curve is exponential in nature. Assuming the theory of heating of homogeneous bodies ,

Heat developed = heat stored + heat dissipated