The paper deals with the implementation of stabilized (longitudinal) differential protection of autotransformers with a tertiary winding, with an emphasis on its three-point protection. Various possible variants of installing current transformers on the tertiary winding (taking into account whether the tertiary is intended for loading or a stabilization winding) and their consequences on the implementation of differential protection of the three-point autotransformer were considered. An example of protecting an autotransformer with a stabilizing tertiary winding, three-point differential protection, using a numerical relay device type RET670 from ABB is shown.