Harmonic Broad band filters (HBF)

When non-linear loads make up more than 80% of the electrical load on a distribution system, some type of harmonic filtering is required to maintain harmonic distortion within the limits. The least complicated filter is a “harmonic Broad Band filter”.


The harmonic filters combine three stages of filtering to achieve wide band attenuation of the harmonic frequencies normally associated with 6-pulse power converters. Two stages of the filter offer series impedance to the flow of harmonics, while the other (shunt) stage diverts harmonics away from the power source. This low pass filter, applied in series with the input terminals of the power converter, permits the fundamental frequency current to flow easily through the filter with very low losses, but is very effective at minimizing the flow of harmonic currents. Both inductors (L) could have impedance > 8%, which means you, could see a 16% impedance in series with load (provide more attenuation to multiple orders of harmonic frequencies). A broad band harmonic filter can easily offer guaranteed harmonic current levels, right at the drive / filter input, as low as to 8% THID. In most cases, this results in less than 5% THID at the facility input transformer and meets most international standards.

  Conversion of P.F. Capacitor bank in to Harmonic Filter:

The heavy duty capacitor is rated for higher continuous over voltage duty than capacitors that are built to meet the basic requirements of shunt capacitor standards. Under many circumstances, a normal shunt capacitor bank made up of heavy duty capacitors can be converted into harmonic filter banks while remaining within the normal over voltage withstand requirements of these standards.

If heavy duty capacitor banks are used in power factor correction, it is easy to convert P.F. capacitor bank into harmonic filter bank by adding iron core tuned reactor in series with P.F. capacitors. The most reliable, low cost solution is often realized with the use of tuning reactor. The filter provides power factor correction at the fundamental frequency and becomes an inductance at the frequencies higher than the tuning point. These harmonic filters are almost always tuned below the 5th harmonic. Therefore, the filter provides an inductive impedance path to those currents at harmonic frequencies created by nearly all three-phase non-linear loads (5th, 7th, 11th, 13th, etc). The De-tuned filter may absorb up to 50% of the 5th & 7th harmonics (depending upon network characteristics).

Since the filter is not capacitive at these frequencies, the plant electrical system can no longer resonate at these frequencies and can not magnify the harmonic voltages and currents. A shunt harmonic filter therefore accomplishes three things:

  • Provides power factor correction.
  • Prevents harmonic over voltages due to parallel resonance.
  • Reduces voltage harmonic distortion and transformer loading at frequencies above its tuning point.

The conversion will be highly economical & efficient to treat harmonics in power industries. Reduce i˛R losses & Heat at utility Transformer.


Tuning Reactor panel is installed very close to existing P.F. capacitor panel either fixed or automatic types. The reactor panel consists of tuning reactors and quantity and rating matching to P.F. capacitor panel. Only interconnections are made between capacitor panel and reactor panel such that each P.F. capacitor is added with appropriate tuning reactor in series. Now the P.F. capacitor panel becomes harmonic filter panel, it filters harmonics and also provides P.F. correction. The reactor panel size is very close to P.F capacitor panel size, it is easy to keep next to P.F. capacitor panel.

  The following information’s are required for us to recommend the suitability of conversion:
  • P.F. capacitor KVAR rating & grid voltage
  • P.F. Capacitor bank is automatic or fixed type.
  • Individual Capacitor ratings (KVAr & Voltage), make & model no & preferably catalogue
  • Distribution transformer ratings- KVA, Voltage, & impedance
  • Harmonic study details at incoming PCC
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