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Harmonics are voltages and currents which have frequency components that integer in multiple of the fundamental frequency – polluting the pure sinusoidal waveform.

Power electronics such as those used in rectifiers, variable speed drives, UPS and host of other equipment draw current in a non-sinusoidal fashion. This non-sine current interact with the main supply and distorts the voltage to a greater or lesser degree depending upon the strength or weakness of the supply.
The greater the amount of installed electronic power switching equipment on- site, more the degree of harmonic distortion.

Problems due to Harmonics

Excessive harmonic distortion of the main supply implies that the source not only carries 50 or 60Hz but also components of higher frequencies.

These components cannot be utilized by electrical equipment’s and cause adverse effects and include

  • Pulsating and reduced motor torque.
  • Limitations on supply and network utilization
  • Malfunctioning of Control system
  • Increased losses

Harmonic Mitigation

PASSIVE Solution

  • Detuned Filters
  • 525V power factor correction capacitor

ACTIVE Solution

  • Without Neutral Compensation
  • With Neutral Compensation

Properties of –


1. Detuned Filters

  • Low loss reactors
  • Integrated thermal switch
  • Blocks harmonic current to flow through capacitors

2. 525V power factor correction capacitor

  • Withstands higher voltage developed when reactor is connected in series
  • Sine-cut technology
  • Self-healing dielectric irreversible over pressure disconnector


  • ADF Dashboard Web User Interface
  • Remote support capabilities
  • Minimized number of spare parts
  • Utilization of existing cabinet space
  • Wide range of ratings in 440V and 690V

Active Filter Solution For Harmonic Compensation of Industrial Loads

AC drives and other non-linear devices produce distortion of both current and voltage waveforms in the supply due to generation of harmonics.
The predominant harmonics in the current waveform are the 5th, 7th, 11th and 13th. These cause increased losses in the supply Tx, power cables and motors directly fed from the supply.
Hence suitable mitigation measures are required to minimize these harmonics. Suitably designed active filters are ideally Suited to such applications.

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  • They are available from 190A up to 400A, with 250A & 310A being the intermediate ratings.
  • The filters are suitable for 50/60Hz operation with an input voltage range of 380V-480V AC.
  • IP-21 & IP-54 enclosures are engineered as standard.
  • Options like Disconnect with fuse and mains shield can be engineered in the same space.
  • They have the same type of cooling arrangement for the power devices as the VLTR drives manufactured by Danfoss.


  • The Active filter is a powerful & intelligent HM tool for use in power system with a large proportion of non-linear loads.
  • It can be used as a central mitigation solution which makes the installation cost effective.
  • It is also capable of compensating for excessive reactive power consumption in the system and can therefore be used to maintain the PF.
  • Selective compensation of harmonics is also possible in systems where a particular harmonic is the cause of high THD.

Harmonic Current (A) – Fabric, Transformer 1 with Capacitor


One of the other commonly followed regulation is IEEE-519, this is another regulation followed by an international Standard organization IEEE (Institute of Electrical and Electronics Engineers). The IEEE-519 states the following limits for harmonics with respect to different voltage level and short circuit capacity of the system as shown in table –

Where, ISC = Maximum short-circuit current at PCC.

IL = Maximum demand load current (fundamental frequency component at PCC).