Demagnetization of a large power transformer based on calculation of the flux linkage

An improved method of demagnetizing high voltage power system transformers is explained theoretically and demonstrated with a prototype test instrument. Because the method relies on the time dependence of magnetic flux linkage to an applied voltage, automation is possible. The amount of time required to demagnetize a transformer is reduced and operator safety is improved. The prototype automatic demagnetizing instrument was tested on a number of different power transformers. The test results indicate that this method is very effective with accuracy as good as ±1% of full magnetization. The tests demonstrate the practicality of automatically demagnetizing a power transformer after winding resistance tests or whenever the magnetic state of a transformer core is in question.