Background: Presented article shows the computation results of accidental off-line turbogenerator energizing. Inadvertent energizing of turbogenerator has been a particular issue in the power plant. The investigated case is three phase energizing. The great emphasis is placed on the physical phenomena existing in the rotor. Material and methods: Finite-element method Field-circuit model of turbogenerator Results: Computations results allow indicate the risks of construction element damages and can confirm the set values of the limits in dedicated protection devices. Conclusions: Computation results can confirm that inadvertent energizing of the turbogenerator can damage the machine if this abnormal operating state is not detected within a few seconds. Achieved results confirm set values in the protection device dedicated for investigated accident both overcurrent and undervoltage relays. The most vulnerable construction element is rotor wedge localized near to rotor big edge Computed maximum density of induced current in conductive rotor parts equals to ca. 140 A/mm2 and can caused increase the temperature above the acceptable limits.