Current transformer as well as protection device and circuit breaker including such transformer

A current transformer (1) suitable for being used in an electrical circuit, comprising: a toroidal core (2) and at least one electrical conductor having a portion (5) passing within the toroidal core; a cooling device (10) having a body made of thermal conducting material and configured so that it has a first portion connected to the electrical conductor at a position upstream from the toroidal core and suitable for absorbing heat from the electrical conductor, and a second portion, spaced apart from the first portion, which is connected to the electrical conductor at a position downstream from the toroidal core and is suitable for transmitting heat to the electrical conductor. The thermal conducting body comprises at least one portion (30) made of an electrically insulating material capable of preventing the current flow through the cooling device itself.