I encountered a passive harmonic filter, PHF with highly non linear loads, i.e. variable frequency drive, VFD (most of the time running 50Hz) serving an induction motor.

PFH full view PFH schematic Inside view

I believe that it is a commonly used resonant shunt filter to eliminate the 5th harmonic.

The enclosure housing the PHF has a ventilation fan, but still always (the reason why I am writing here) very HOT! Up to the extent that the contactors, wires have melted/discolorated/burnt mark etc

Fan, but still very hot. Bubbling insulation Thermoscan shows 86C!

I suspect of the over saturation of the 3 phase transformer (V_phase2phase=415V), I believe acts as an isolation transformer-cum-line reactor. The capacitors are still in good condition (not bulging of the caps), but the winding insulation of the transformer is discoloured.

Sagging insulation Discouloured connectors Capacitors

Any help to do further diagnostic is welcomed. I will conduct a harmonic assessment with a Fluke power analyser next week.

  • \$\begingroup\$ Is the motor and/or VSD overloaded? \$\endgroup\$ – Li-aung Yip Mar 21 '15 at 10:31
  • \$\begingroup\$ Also, have you used the thermal camera to make sure it's not just a hot joint? \$\endgroup\$ – Li-aung Yip Mar 21 '15 at 11:00
  • \$\begingroup\$ Does it get hot off-load? \$\endgroup\$ – Andy aka Mar 21 '15 at 11:20
  • \$\begingroup\$ @Li-aungYip: thanks for the comment. This filter has been installed for the past two years, and the motor & VSD are of 30kW, may not be undersized issue(I'll confirm again). Not sure if it's overloaded, most likely not as it is a factory designed and other similar units are not facing the same issue. Will need to check again if it's under-designed. How may I know if it's not just a hot joint? And it's not hot off load.... \$\endgroup\$ – kitkit Mar 21 '15 at 12:41
  • \$\begingroup\$ and @Andyaka: thanks for the comment. It's not hot off load, as the motor and filter are OFF. Why do you say/suspect otherwise? \$\endgroup\$ – kitkit Mar 21 '15 at 12:42

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