Partial discharge (pd) is one of the main driving factors of long-term degradation and electrical insulation failure. PD energy dissipates primarily as heat, but also as sound and light. Heat insulation degrades when it gets too hot. Although the partial discharge energy is small, it can occur hundreds or thousands of times per second at the same location.

In addition, ozone that eats away at the insulation is produced in the process, and ruptures related to chemical damage to the insulation occur, and the electrical conductivity of the insulation surrounding the gap in the insulation increases. PD can also lead to a "tree" in the insulation layer of the cable. A tree is an electrical discharge channel that extends over time from one part to another, like a branch of a tree.

If the inverter driver power system is not used correctly, the partial discharge may occur thousands of times per second, which may lead to the failure of the motor in hours, weeks or months.

Bottom line: partial discharge can lead to gradual deterioration of insulation material and eventually lead to electrical breakdown. Please note that, especially in high pressure equipment, a low level of PD may be good.

When and where partial discharge occurs

When exposed to the electric field, when the electrical stress exceeds the critical value, instantaneous gaseous ionization will occur in the tiny voids of the insulating system. This ionization, coupled with a sufficiently high electrical stress, produces a partial discharge.

As shown in the figure, the gap can be anywhere. With insulation, the chance of space between layers increases.

Partial discharge may also occur on the insulating surface. Second-hand rotating equipment usually has a layer of pollution outside the insulation layer. If this "dirt" or moisture on the insulating surface is uneven or discontinuous, the surface may discharge. This is especially true if there are contaminated insulation cracks or highly conductive paths from the conductor to the insulator surface, as shown in the figure below.