A harmonic filter is a special filter designed to reduce the levels of harmonic current drawn by VFDs and other electronic equipment.
Harmonic filters are used in some installations because the harmonic levels are too hgh and are causing problems with other equipment.
Additionally, in some parts of New Zealand, the power authorities have made the use of harmonic filters mandatory due to the cummulative effect of many VFDs connected to their supply. In these areas, the use of harmonic filters on VFDs is required and not negotiable. The standard regulations require harmonic filters on all new installations greater than 22KW.
Harmonic currents are caused by non linear loads and appliances. Commonly, the non linear components are solid state rectifiers used in all manner of modern equipment.
The most common source of major harmonic currents are the rectifier circuits in variable frequency drives, and the rectifier circuits in switchmode power supplies as are used in many industrial supplies and most modern domestic appliances and computers.
Harmonic voltages are generated by the action of harmonic currents on the impedance of the electrical supply.
Harmonics on the electrical supply system cause increased losses and can excite resonance in some circuits resulting in elevated voltages.
Harmonic voltages will cause harmonic currents to flow in resistive loads that are proportional to the harmonic voltage, but in capacitive loads, the harmpnic currents will increase as the frequency of the harmonic increases. This is because the impedance of a capacitor is inversely proportional to the applied frequency. The increased current in capacitors will increase the capacitor heating and can cause premature failure
Harmonic voltages cause an increase in harmonic current into the motor and increase the losses in iron cored components and can cause a major increase in the rotor slip losses of an induction motor.
Supply distribution transformers must be derated in the presence of harmonic currents in order to avoid transformer over heating.
Harmonic currents cause a distortion power factor less than 1.0 and this affects the supply in much the same way as a displacement power factor.
see : What do harmonics do?
There are a number of different types of harmonic filter and some work better than others.
For more information, see http://www.power-harmonics.co.nz
The Mirus Lineator has a guarantee that it will meet the requirements of the local regulations.