OMICRON

Partial discharges (PD) occur in the stator insulation system of rotating machines, where local electric field stress exceeds the local electrical strength. PD measurement of rotating machines can be performed on-line (i.e. during regular load or no-load service operation) or off-line (i.e. during standstill of the machine, by energizing each winding successively). The insulation materials typically used for rotating machines are resistant to a certain level of Partial Discharge. Consequently, a large quantity of PD pulses might be expected in all phases under normal operating conditions. However, certain Partial Discharge may indicate aging or production-caused defects in the insulation, or damage to the winding structure: Loose coils or deteriorated semiconductive or graded coating may result in slot PD, insulation voids or delamination may create internal Partial Discharge, moisture or contamination of the winding will create surface PD. Generally, several different Partial Discharge sources are active within the stator winding insulation at the same time.

Thus, the key to successful PD measuring in stator windings is the separation of parallel active PD sources and distinction between harmful PD, normal PD occurrences and outer noise, inevitably present in industrial surroundings.

Engineers use the synchronous digital multi-channel PD measurement system MPD 600. It operates with three or more synchronized channels to separate inner PD sources from each other and from noise signals, and evaluates each PD source within the stator winding individually.