An oil paper insulation dominant 
time constant calculation method based on an extended 
Debye equivalent circuit sequentially comprises the following steps: the step 1, performing preparation work comprising powering off a 
transformer to stop operation, enabling various phases of high- and low-
voltage windings and a neutral point to be in short connection and be grounded, and then releasing residual charges; the step 2, obtaining data comprising setting a 
polarization voltage and a charging and discharging 
time ratio, performing wiring, and performing a 
recovery voltage test experiment on the 
transformer by utilizing an RVM5461; the step 3, selecting a 
shuffled frog leaping algorithm, and establishing an 
evaluation function to solve an 
equivalent circuit parameter; the step 4, calculating 
peak value measurement time through adoption of segmented Hermit interpolations for 3 times, and obtaining a continuous 
recovery voltage polarization spectrum according to a 
recovery voltage calculation formula; and the step 5, searching a peal value of the recovery voltage polarization spectrum to determine a dominant 
time constant. The problem of insufficient accuracy of a non-standard polarization spectrum dominant 
time constant in actual measurement and the problem of long consumed time in the actual measurement are overcome, and accuracy of diagnosing a 
moisture content of an 
insulation system by utilizing the dominant time constant is improved.