Electrical discharges occur inside and on the surface of medium and high voltage insulation, and are the result of flaws, cracks, voids and irregularities. These imperfections create voltage stresses and eventually cause failure of the insulation. Insulation failures begin and are characterized by small detectable releases of energy or partial discharges.

Partial discharges are indications of insulation degradation and occur in electrical systems that are 600V and higher (2.4KV, 4.16KV, 12KV, etc).  The types of electrical equipment vulnerable to partial discharge includes, but is not limited to, switchgear, generators, transformers, instrument transformers, motors, circuit breakers, cables, and cable connections.

Table 36 of the IEEE Gold Book on Electrical reliability indicates that 84% to 95% of transformer, switchgear bus, bus duct, cable and cable splice failures are caused by insulation breakdown. Regular partial discharge testing can prevent these failures from occurring.

The Insulation Quality (IQ) Program allows the insulation quality of medium and high voltage equipment to be tested without requiring an outage, and is non-destructive.  Valuable information is recorded & analyzed to determine equipment condition which allows maintenance activities to be planned and prioritized. Regular testing allows comparison of recent tests with past records for trending analysis. Trending identifies when a problem started and how rapidly the problem is progressing. Partial discharge testing ensures system reliability. This method of evaluating electrical equipment maximizes system productivity by protecting the facility from  random medium and high voltage electrical failures.