Power Quality Issue

[usman14865]

Hello engineers, I am facing a PQ issue at one of Textile plant having non linear loads, when Switching ON certain stages by Automatic PF relay, the Installed 800 KVAR Passive filter at LV substation creates loud humming noise, overheating of reactors/capacitors and occasional blown fuses, etc, some times no noise is observed if some stages are turned ON manually; due to fear of fire customer has kept it turned OFF, P.F can’t be improved. Panel Analyzer shows THDI before switching Passive filter ON = 9% and after switching passive filter ON = 13% (all 12 stages On. Due to fear of fire customer has kept it turned OFF, P.F can’t be improved.

Does Resonance could still happen at installed anti-resonance passive filter with 7% detuning factor? Is the design of passive filter incorrect? or it has gone incorrect after installation of additional unplanned non-linear loads over a period, or there could be other reasons causing it, we want to avoid expensive AHF solution, opinion from forum members is requested.

 

[paulengr]

Hello engineers, I am facing a PQ issue at one of Textile plant having non linear loads, when Switching ON certain stages by Automatic PF relay, the Installed 800 KVAR Passive filter at LV substation creates loud humming noise, overheating of reactors/capacitors and occasional blown fuses, etc, some times no noise is observed if some stages are turned ON manually; due to fear of fire customer has kept it turned OFF, P.F can’t be improved. Panel Analyzer shows THDI before switching Passive filter ON = 9% and after switching passive filter ON = 13% (all 12 stages On. Due to fear of fire customer has kept it turned OFF, P.F can’t be improved.

Does Resonance could still happen at installed anti-resonance passive filter with 7% detuning factor? Is the design of passive filter incorrect? or it has gone incorrect after installation of additional unplanned non-linear loads over a period, or there could be other reasons causing it, we want to avoid expensive AHF solution, opinion from forum members is requested.

Don’t care about %THDI. That’s meaningless. What is your %THDV? %TDDI? A rectifier will generate 30% THDI but if the transformer is nowhere near loaded it doesn’t matter.

BUT it sounds like you have a huge problem. Outright capacitors cannot be used with high harmonics. Your 60 Hz power factor correction becomes a dead short at higher harmonics. That is the sound you are hearing as it resonates...very dangerous. I’d tell you to shut it down too. You can’t just Willy nilly install cap banks ever without paying attention to the loads. The fact that you have nonlinear loads should be a huge red flag.

The way out is you have to use a harmonic filter and NOT just a capacitor tuned to an off harmonic such as the 4.7th. Usually harmonics in the 4th to 5th range are used. That’s if you don’t have VFDs. Those can be good at one speed and bad at another. You may have to move it to a safe location downstream. This is the problem with one big “automatic” cap bank. It is far better to go after the big Var loads and put passives just on those. That way upstream the harmonic “problem” doesn’t happen.

 

[NewtonLaw]

Would you be able to show us a partial one-line diagram of the system that in includes the supply to the service transformer, transformer nameplate data, wire size, wire length, capacitor nameplate data, voltages, load types. This would help us to answer your question a little better.
In my opinion, you may be experiencing a form of ferroresonance depending on location, transformer size, available short circuit current. If you can supply this it may help.