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Determine Your Motor or Generator Condition with Online Partial Discharge Monitoring 

The Iris Power GuardII provides you continuous online monitoring of partial discharges in your stator winding insulation and generates diagnostic reports so you can take action prior to irreversible damage or failure.  The GuardII also has a flexible, modular design that can incorporate monitoring of partial discharge, rotor magnetic flux, endwinding vibration as well as shaft voltage and current to help you plan your maintenance.

Causes of Partial Discharge in Motors and Generators


Partial discharges (PD) are small electrical sparks that occur within the high voltage electrical insulation in motor and generator stator windings as well as dry type transformers, and switchgear operating at 3kV or higher.


Partial Discharges occur when there are small air gaps or voids in or on the surface of the insulation where the electrical forces are greater than the dielectric strength of gas (equal to about 3kV/mm at 1 atmosphere).


Normally, a well-made equipment that is in good condition displays very little partial discharge activity. However, insulation deteriorates due to vibration of loose winding, operation at high temperatures, contamination from bearing oil, moisture and load cycling.


Importance of Partial Discharge Monitoring


Industry statistics by IEEE and EPRI (Electrical Power Research Institute) indicate that approximately 40% of all rotating machine failures occur due to failure of the stator winding insulation. Partial Discharge monitoring is the only on-line electrical test that correctly identifies and warns of pending stator winding failure.


Stator end-winding vibration monitoring can also provide benefits that may include:

  • Avoiding unexpected in-service failures of the stator winding insulation prior to planned outages
  • Extending up-time between outages by avoiding unnecessary maintenance
  • Identifying problems on new machines which may still be under warranty
  • Identifying the quality of repairs or rewinds
  • Focusing maintenance on machines in the fleet with high levels of vibration


Methods For Partial Discharge Monitoring



Sensor Installation - Bus Couplers

Bus Couplers are 80pF epoxy mica capacitors that are typically used for motors and small turbo generators (less than 100 MVA) to allow only high frequency (>40MHz) signals to pass through for analysis. The configuration and processing of the signal is setup so plant noise can be identified and removed, leaving only the true partial discharge for analysis and diagnostic reporting.


Sensor Installation - Stator Slot Couplers

For turbo generators of 100MVA or larger, Stator Slot Couplers (SSC) are permanently installed under the line end stator winding wedges in existing machines, or between the top and bottom bars in new or rewound turbo generators. Stator Slot Couplers are the most sensitive partial discharge sensors in the world as it eliminates both internal and external noise. The Iris Power SSCs are not connected to the high voltage winding and are not subject to any high electrical stresses. The high frequency bandwidth ranges from 10-10,000 MHz.


Data Acquisition and Monitoring

The Iris Power GuardII systems perform continuous monitoring and analysis of partial discharge measurements, rotor magnetic flux and end-winding vibration. The GuardII uses unique and rigorously researched methods to overcome the electrical interference (noise) typical in most plant environments ensuring that the diagnostic outputs are based off reliable and repeatable measurements and can easily be compared to the Iris Power database of over 400,000 test results. The collective experience and results of Iris Power clients are regularly summarized in statistical tables, available to all users. This is a service unique to Qualitrol-Iris Power and its clients and ensures objective interpretation of insulation condition.


Iris Power | Training 2016



Partial Discharge Training Course

Register to attend the next course on Partial Discharge in Houston Texas from April 12-14th. 


Iris Power | Case Study



Case Study

Continuous Partial Discharge Monitoring Detects Manufacturing Defect Within Warranty Period






Iris Power | GuardII Brochure

The GuardII provide continuous online monitoring of partial discharge with modular options to rotor magnetic flux, endwinding vibration as well as shaft voltage and current. 


Yes, please contact me regarding your Partial Discharge Solutions