ABSTRACT
In the United States, a large percentage of transmission systems was installed during World War II between the mid-1950s and the mid-1970s, with limited construction in the past few decades. The equipment installed in the postwar period is now between 30 and 50 years old and is at the end of its expected life. For example, 70% of transmission lines and power transformers in this country are 25 years old or even older. Similarly, 60% of HV circuit breakers are 30 years old or older.
