Improvement of permissible loading of transformers

The permissible loading of transformers is determined by internal losses, radiated heat from sun exposure and radiation and convection heat losses. In countries with high temperatures and high solar radiation, the transformer rating can be increased by solar shield preventing the heating through solar radiation. For 237 transformers (HV/MV) the influencing factors are discussed and analyzed and a cost comparison and economic evaluation was carried out. The results indicated that solar shielding is applicable for transformers with rating above 18MVA, as the cost for the shields will be lower than the cost benefit for the expected transformer life time of 20 years.