What is the Average Life Expectancy of a Transformer ?
Normal or Average Life Expectancy of a Transformer
In short “until it fails” as some of the transformers are still in operation after the legal retirement of plant engineers and technicians. 
When a transformer is operated under ANSI / IEEE basic loading conditions (ANSI C57.96), its normal life expectancy is about 20 to 30 years. The ANSI / IEEE basic loading conditions for Transformer are:
- The transformer is continuously loaded at rated kVA (kilo Volt Ampere) and rated voltages (transformer must be operated at the rated voltage and kVA)
- The average temperature of the ambient air during any 24-hour period is equal to 30°C (86 °F) and at no time exceeds 40°C (104 °F).
- The height where the transformer is installed, does not above 3300 feet or 1000 meters.
Related Post: Power Transformers Maintenance, Diagnostic & Monitoring
Normal Life of Dry Type Air Cooled Transformer
Dry type transformers are everywhere. They are looking innocent (but they are not). Most of the people around think they are metal enclosure with a humming noise. Keep in mind that that these types of transformers are fatal.
The average life span of general purpose dry type transformers are more than 25 years. If an air cooled dry type transformer operated in dust free, well ventilated avoiding direct hit, dust, wet and humidity with rated parameters, it may last more than 35 years even 50+ years.
The normal life span of Indore 100kVA enclosed air cooled transformer is more than 60 years as they are well maintained and operated with rated parameters and installed in looked electrical rooms.
According to the ANSI Standard C57.12.96, the life expectancy of a low voltage dry type distribution transformer can be 20 to 30 years or even longer under various loading conditions. The exact age of a transformer life depends on multiple factors such as, various loading, manufacturing quality, insulation classes and environmental conditions etc.
As dry transformer is a static device with no moving parts, it has a trouble free life under normal operating conditions. There are multiple insulation classes such as Class A (105°C), Class B (130°C), Class F (155°C), Class H (180°C ) and Class R (220°C) and the proper one should be selected according to the needs and design for reliable transformer operation and life.
According to the TEPCO (Tokyo Electric Power Company) survey, the life expectancy of HV and EHV transformer are 65 years and 75 years for distribution transformer in the current network.
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