Thermal protection of transformers under overload conditions

THE AIEE transformer subcommittee¹ has recommended higher overloads than those given in the ASA Guides for operation of transformers. These overloads are set up on the assumption that, under rare emergency conditions, it is better to use up a small amount of the expected life of the transformer than to have an interruption of service. Therefore, as a result of the work of the AIEE and the ASA, a demand is developing for a relay that will close its contacts when the limiting load condition is reached.