When to replace aging transformers

Transformers play critical roles in delivering power to distribution equipment for homes, commercial establishments and industrial facilities. Sudden failure of a transformer can have many serious repercussions leading to loss of power for a few minutes to hours. There are instances an outage could last for weeks because of system configuration, such as a simple radial system or the transformer was the single point failure. In industrial complexes an outage lasting a few minutes could lead to loss opportunities as well as millions of dollars in lost production and start up costs. Many older transformers have been in operation for more than 80 years without failure or major problems. Although there have been recent failures of units producing fires and explosions resulting in the release of toxic and combustible gases as well as smoke into the atmosphere; also OSHA has levied fines because of the type of incident. Many transformers in the petrochemical industry now fall under OSHA 1910.119, Mechanical Integrity regulations due to probability of catastrophic failure during power loss, resulting in release of highly hazardous chemicals. Transformers tanks containing more than 10,000 pounds of aggregates in some cases fall underneath the 1910.119 as well as 1910.269 regulations. Mineral oil in transformers is used as a media for cooling and insulating parts within close proximity. Mineral oil has a NFPA flammability rating of 1, indicating it is slightly flammable with a health rating of 1 as well, indicating a slight health hazard. However, during fault conditions mineral oil can be hazardous to your health and the environment. The purpose of this paper is to provide information and insight related to repair or outright replacement of aging transformers containing mineral oil under fault conditions such as the production of combustible gases. This paper will explain how oil sampling, gas analyses, internal inspection and testing were used to determine which required replacing or simple repairs. It will explain the use of standards such as IEEE C57 guidelines, to determine loading, hours of operation, degradation and other tests used to evaluate conditions and suitability for future operation of transformers. It will discuss the use of insulation power factor, Furan and other tests to help predict remaining life in transformers. It will discuss life cycles and vintage of transformer produced in the 1950's versus those manufactured for our facility after 1990. There will be discussions about methods, local repair shops employed to test and evaluate transformer incoming conditions and suitability for future service.