The HFCT is a high frequency current transformer designed specifically for picking up partial discharge signals. It has a split core ferrite to allow retrospective fitting to earth straps without the need for disconnection. The durable body has a hinge and a quick release latch, making use quick and easy. The HFCT is constructed with an aluminium body to provide RF shielding and improved performance in noisy environments.

Partial discharge activity in solid high voltage insulation induces small high frequency currents in the earth conductor of the electrical system. These impulses travel along the equipment earth to the substation earth. Using a high frequency current transformer they can be detected as they pass through the CT.