Re: Harmonic filter for better power quality

Home Electrical Engineering Forum General Discussion Harmonic filter for better power quality Re: Harmonic filter for better power quality


Hi, Alen,

Sorry for the late response. I was answering another comment when I saw your question.

I’m not able to see the details of load sizes in your attachements. So, I will make general comments.

Using power factor capacitors (PFC) with detuning to make 5th and 7th harmonic filters is always questionable. The reason is the amount of leading VARs injected by the two filters. If often exceeds the required VAR injection and leading displacement PF occurs. Leading PF can cause the safety devices (circuit breakers and contactors) to fail over time. Also, if the leading level is high enough other customers or the utility may experience resonance. You will see elevated mains voltage levels.

Schneider Electric generally recommends the following regarding nonlinear load content:

a) If the nonlinear content of total load is less then 15%, then standard PF capacitors can be used.

b) If the nonliear content is between 15 and 50% of content, then detuned PF capacitor systems are used.

c) If the nonliear content exceeds 50% of content, then actice harmonic filters are used for PF correction.

It sounds like (based upon your brief description) that your nonlinear content is over 50% of the total load. If so you may need some displacment PF correction but not as much as paralleld 5th and 7th order filters will inject.

Active harmonic filters (AHF) inject controlled reactive current for displacement PF correction and harmonic mitigation. Current transformers are used to define the load current so AHF inject only what is required to attain the set point displacment PF and 5% TDD for harmonics. There is no chance of over correcting displacement PF and thus no chance of leading PF.

I suggest you contact your local Schneider Electric specialists for assistance.

Regrads, Jim