An eddy current sensor for conductor inspection on energized power lines

This paper describes an eddy current sensor carried by a corrosion detection robot that operates on energized power lines. The robot is installed on a live overhead conductor and it is controlled by the ground-based operator using a portable computer and a radio link. The sensor carried by the robot is capable of detecting the remaining thickness of the zinc layer over the steel wires that make the core of the aluminum conductor steel reinforced (ACSR) commonly used in power lines. The sensor is made of a contactless coil that encircles the conductor and applies an alternating longitudinal magnetic field along the conductor. This field induces eddy currents in the zinc layer that changes the coil impedance, which is used to obtain the zinc layer thickness. The main sensor characteristics are described in this paper, such as its immunity to the load current, its enhanced sensibility due to a hybrid circuit, and its contactless coils that facilitates the sensor installation on the power line conductor.