Active Harmonic Filter to improve equipment operating live

Omniverter AHF is one of a few active filters in the market that can be configured as a 3-wire or 4-wire configuration.

3-Wire Configuration – Commonly installed at industrial applications like VFD's.

4-Wire Configuration – Commonly installed in commercial buildings to eliminate harmonics (triplen 3, 9 & 15..) generated by switch-mode power supplies and IT equipment. They correct triplen harmonics in the neutral conductors.

A harmonic distortion is a form of pollution in an electrical system. A harmonic voltage or current waveform is a sinusoidal wave whose frequency is an integer multiple of the fundamental frequency. For example, the 2^rd order harmonic frequency for a 60Hz system is 180Hz, 5^th is 300Hz, 11^th is 660Hz, etc.
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The characteristics of the different frequencies impact the fundament voltage and current waveform as shown in the image below.

The waveform distortion is expressed in Total Harmonic Distortion as a percentage. THD or THDi is a measurement of the harmonic distortion present and is defined as the ratio of the sum of the power of all the harmonic components to the power of the fundamental frequency.
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Harmonic generation is generally found in circuits with power electronics devices (non-linear loads). For example, rectifiers or variable frequency drives and switch-mode power supplies.

Harmonic distortion can damage equipment over time. It pollutes the electrical supply's quality and adds additional electrical noise that affects the power quality.

The following scenarios are some of the failures that are common when the THD is above the recommended levels:       
- Interference with communication, sensors and automation control equipment
- Overload and overheating of transformers
- The circuit breaker and fuse may be affected for unknown reasons
- Degradation of motor bearings

Harmonics can be produced in a plant and/or it maybe transmitted  from the utility supply. In practice, it is difficult to determine who is responsible for the harmonic distortion as it depends both on the utility supply (impedance) and the customer (load current). Therefore, detailed analysis is required to determine the source of distortion.

Power Quality analyzers installed permanently are advisable to measure and monitor if the THD levels are within the compatibility criteria according to the  IEEE 519 standard.

There are several methods to filter or trap unwanted harmonic frequencies. Some methods include filtering the harmonics generated at the source, while other options exist to trap upstream and downstream harmonics at a specific voltage bus.

An active harmonic filter monitors the load current and dynamically provides controlled current injection (180 degrees opposite), which cancels out the harmonic currents generated within the plant. AHF do not correct harmonic distortion coming from the utlity supply.
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A passive harmonic filter using a series of capacitors (capacitance) and reactors (inductance) forms an LC circuit parallel to the power source. This is also called a trap filter which absorbs the harmonic currents to which it is tuned. A detailed PQ study is necessary to ensure the filter will not cause a resonance condition on the power system.

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