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 threephase nonlinear loads (5th, 7th, 11th, 13th, etc). The Detuned 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.
