The PD-SG1 is a dual transducer Switchgear PD detection instrument. The unit detects TEV signals generated by internal discharge, as well as acoustic discharge generated by surface tracking or corona. Partial discharge activity inside metal clad high voltage plant induces small voltage impulses (called Transient Earth Voltages) on the surface of the metal cladding. TEVs travel around the cladding surface to the outside of the switchgear panel, where they can be picked up externally using capacitively coupled transducers.