According to IEC 60270 a Partial Discharge (PD) is a localized electrical discharge that only partially short circuits the insulation between conductors and which may or may not be adjacent to a conductor. This wide definition includes from relatively harmless partial discharges to others that are difficult to detect in the field or not to be detected, over time can be very destructive, producing the damage of the insulation system that finally causes a short circuit, and this in turn may damages electrical equipment, power outages, fires, and explosions.
OSLINGER S.A.S has highly qualified personnel and the most important techniques available in the world market for the measurement, classification and localization of PD in electrical machines. This allows us to conclude with respect to the state of the insulation system and to take corrective actions of maintenance, repair or replacement of winding or equipment before a failure or loss occurs.
Partial Discharges are developed in places where the dielectric properties of the insulation material are not homogeneous. In these places, there is a local concentration of the electric field lines, which once the electric current of local rupture is exceeded and free electrons appear, results in the ionization process and later avalanche of electrons or current flow, thus giving rise to a partial discharge which is finally detected in the outer circuit. Figure 1 shows typical defects in the stator winding that cause partial discharges.

Figure 1. Sources of PD in stator insulation.

Figure 1. Sources of PD in stator insulation.

The measurement and analysis of Partial Discharges is considered as one of the best indicators of incipient insulation system degradation faults, which provides a warning against insulation failures.
One of the most widely used partial discharge analysis techniques is the Phase-Resolved Partial Discharge (PRPD), this analysis allows to identify some of the most common degradation mechanisms, since there is a strong relationship between the shape of the pattern and the type of defect that causes it. It relates the magnitude of the DP pulses, the occurrence phase and the number of pulses detected. In Figure 2 is shown the typical resolved phase diagram for internal partial discharges which are produced by cavities inside the insulation of the winding as shown in Figure 3.



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