Transformer Cooling System:

Transformer Cooling System (Large Units) – Basically, there are two seats of losses in a transformer namely:

• Core, where eddy current and hysteresis losses occur (caused by alternating density).
• Windings (primary and secondary) where I²R or copper loss occurs because of the current flowing in these.

Heat due to losses must be removed efficiently from these two main parts of the transformer so that steady temperature rise is limited to allowable figure imposed by the class of insulation used. The problem of cooling in transformers (and in fact for all electric machinery) is rendered increasingly difficult with increasing size of the transformer. This is argued as below:

The same specific loss (loss/unit volume) is maintained by keeping constant core flux density and current density in the conductor as the transformer rating is increased. Imagine that the linear dimensions of transformer are increased k times. Its core flux and conductor current would then increase by k² times and so its rating becomes k⁴ times. The losses increase by a factor of k³ (same as volume), while the surface area (which helps dissipate heat) increases only by a factor of k². So the loss per unit area to be dissipated is increased k times.

Larger units therefore become increasingly more difficult to cool compared to the smaller ones. This can lead to formation of hot spots deep inside the conductors and core which can damage the insulation and core properties. More effective means of heat removal must therefore be adopted with ducts inside the core and windings to remove the heat right from the seats of its generation.