Hydraulic-driven underground self-propelled cable tool pipe column

A downhole self-propelled wireline tool string (1) for advancing a tool in a well (2) and/or for providing weight on a drill bit, the downhole self-propelled wireline tool string comprising a first downhole self-propelled wireline tool (1 a), comprising: a first tool body; a first electric motor (4) operating at a rotational speed; a first electronic control unit (18) for controlling the rotational speed of an electric motor, the downhole self-propelled wireline tool string further comprising a second downhole self-propelled wireline tool (1 b), comprising: a second tool body (3 b); a second electric motor (22) operating at a rotational speed; a second electronic control unit (18 b) for controlling the rotational speed of the electric motors, wherein each electric motor comprises a power limiting unit for distributing a first portion of the current from the cable for powering the first electric motor and a second portion of the current for powering the second electric motor.