At this Special Issue will be offered a technique of estimation a technical condition of electric machines insulation, based on subtractive clustering of partial discharges (PD) pulses, which registered at stationary and transient operation modes.

The suggested technique, at difference from other on-line monitoring systems, allows estimating the technical condition of winding insulation in real time, when transient beginnings and accompanied the enhanced electrodynamics, thermal and vibration loading that allow reveal defect in insulation at early stage. The operators with special training to perform the offered technique of PD cluster analysis is not required, as this can be done specially designed real-time expert system.