method for estimating transformer residual magnetic flux and device for estimating residual magnetic flux. After testing and site inspections involving dc voltage being applied to transformer windings, a method for estimating residual magnetic flux of transformers and a device for estimating residual magnetic flux to estimate residual magnetic flux is described. a residual magnetic flux estimation device (1) provided with a dc power supply control device (300) for applying a dc voltage between two terminals of a 30 connection, which is a secondary winding or a tertiary winding of a voltage measuring device (12) measuring terminal voltage on the primary side of a three-phase transformer (200), a computational device (13) for determining an fse that has a high voltage between the two different phases of the phase at which the voltage is applied, and a residual magnetic flux measuring device (14) that measures the line comprising the two different phases of the determined phase that will have the maximum residual magnetic flux.
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