A petroleum well injection system is provided for an intervention cable with a well tool ran into or out of a well during a well operation. The system includes a blow out valve BOP connected to a well head at a well, a lock chamber at the BOP arranged to contain the well tool before and after the well operation, an injector for the intervention cable, with drive belts driven by an electric motor, and a sensor for measuring the injector force or the tension that the drive belts applies to the intervention cable, a guide arch at the injector, wherein the intervention cable runs taut over the guide arch to a first end of the closed bending restrictor channels, a guide arch load cell arranged to measure the backward tension between an intervention cable the first end of the bending restrictor channel, and wherein the other end of the bending restrictor channel is connected to a drum frame with a motor running a drum for the intervention cable.