Partial discharges are small electrical sparks that occur within the electric insulation of switchgear, cables, transformers, and windings in large motors and generators. Partial discharge analysis is a proactive diagnostic approach that uses partial discharge (PD) measurements to evaluate the integrity of this equipment. Each discrete PD is a result of the electrical breakdown of an air pocket within the insulation. PD measurements can be taken continuously or intermittently and detected on-line or off-line. PD results are used to reliably predict which electrical equipment is in need of maintenance.