What is the base temperature rise of a transformer?

Frequently Asked Questions Autotransformer MV Transformers 

The base temperature rise of a transformer is the maximum temperature rise at the expected full load capacity. Transformers can be built to run cooler than the base temperature rise, these are typically referred to as lower temperature rise transformers which can either operate in higher ambient temperatures or have additional service factor.

  • 105C Insulation System: 55C Base Temperature Rise
  • 150C Insulation System: 80C Base Temperature Rise
  • 180C Insulation System: 115C Base Temperature Rise
  • 220C Insulation System: 150C Base Temperature Rise

The Hot Spot Allowance is added the expected ambient temperature and full load temperature rise to get the total expected temperature rise of a transformer.