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


Jim Johnson said:

Thanks for the compliment. The subject is not simple – it gets tough to make it simple.

A PF capacitor when placed in an electrical system has a resonant frequency based upon the inductance of the electrical system (from any point) and the capacitance of the PF capacitors. The PF capacitors are installed parallel to the loads. Adding a reactor in the parallel portion of the circuit in series with the capacitors modifies the frequency of the PF capacitor bank and thus the resonant frequency of the PF capacitor bank in the electrical system. This is 'detuning.'

PF capacitors will interact with all frequencies present in the electrical system. When harmonics are present this is harmfull to the capacitors. The harmonic currents will overheat the PF capacitors to shorten its life or trip its thermal safety devices. Detuning can be designed to 'block' most of the harmonic currents or can be designed to permit the current of one harmonic frequency to flow into the capacitors. The 'blocking' design is considered 'detuned' within the industry. The design that permits a harmonic order to flow into the capacitors is called a 'tuned' capacitor or a harmonic filter.

Detuned and tuned capacitor systems are typically of two application philosophies. One is an electrical system solution where one large bank is used for a group of loads or used at the utility connection. Local and worldwide suppliers of these exist. However, a harmonic study is required for these types of solutions. Be sure the company chosen can provide this before equipment is purchased.

The second philosophy is to place a small tuned capacitor system at each nonlinear load to provide harmonic suppression for the electrical system. To be sure that these small tuned banks do not interact with each other (when more than one is installed) or overload due the presence of other sources of harmonics, a series reactor on the source side of the filter section is required. The series reactor is sized for the full load current of the nonlinear load on which applied.

The tuned filter also provides leading reactive current that must be evaluated within the system to determine if problems may occur due to excessive leading PF. The manufacturers of these type of filters tend to be localized operations within individual conutries. They exists in many countries.

The result of properly applying either device will relieve the utility of conducting VARs and specific harmonics and permit green generation technologies to be more easily employed.


wull i want to know one thing that i am choosing my final year project
on design an fabrication of power factor improvement pannel, well after
reading these all topics i am confused that , in this pannel which is
basically for industries, should i use harmonic filters also or not? and
one important thing what change can i bring in my project?