2.2 LIFETIME SURVEY
The lifetime survey of power circuit breakers installed in Thailand transmission network at voltage level of 115, 230 and 500 kV is presented in Figure 1 as age distribution and cumulative frequency.
The total number of power circuit breakers is 2,899 units. From Figure 1, approximately 18.55% of total circuit breakers or 538 units have age more than 24 years. In general, the average lifetime of high voltage asset is 25 years. Thus, these units should be replaced soon regarding to age consideration.