Why Use Partial Discharge Monitoring ?
The reliability record of large high voltage Machines is generally good. However, experience has shown that when failure does occur it is generally caused by a breakdown in the Stator Winding Insulation.
Regular monitoring of a machines condition, utilizing on-line Partial Discharge Analysis will lead to improvements in plant economy, availability and useful operating life. On-line monitoring of discharge activity in the structure of a stator winding will produce an accurate indication of the deterioration process. Regular monitoring provides the opportunity for early detection of problems and possible remedial action thereby prolonging the life of the machine.
The life expectancy of a High Voltage machine will depend on various factors acting either singly or in combination to modify the discharge characteristic of the winding. This is why ERIKS using the Rogowski Coil method of gathering and analysing Partial Discharge activity are able to accurately predict the degradation process and the effect discharge erosion plays on the Stator Insulation System.
The illustration above depict the trace obtained from a High Voltage Motor with Slot Section Movement and also the effect that this movement had on the coils below.
All high voltage machines operating at 6000 volts or more generate some degree of discharge. By measuring this discharge we can 'trend' the condition of a machines insulation system.
ROGOWSKI COIL © Partial Discharge Analysis will detect:-
The accumulation of contamination on the surface of the endwindings reduces the resistivity of the winding.
Detects voids in the insulation structure.
Measures and detects Phase-Phase discharges.
Surface contamination may permit the flow of substantial current in the surface film leading to carbonisation of the underlying insulation surface.
End Winding Movement
Brought about by severe starting duties leading to fatigue failure of the tape structure.
Slot Section Movement
Loose Slot Wedges allowing tangential vibration at rotor slot passing frequency causing abrasion of the coil sides against the slot wall.
The Rogowski Coil ©
is totally non-invasive, requiring no direct connection to the High Voltage circuit, and provides natural rejection of discharge signals generated by other machines connected to the same supply system.